v3.24.0.1
Insurance Liabilities - Undiscounted, Incurred and Paid Losses and Allocated Loss Adjustment Expenses (Details)
$ in Millions
 12 Months Ended
Dec. 31, 2023
USD ($)
country
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Dec. 31, 2020
USD ($)
Dec. 31, 2019
USD ($)
Dec. 31, 2018
USD ($)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Dec. 31, 2015
USD ($)
Dec. 31, 2014
USD ($)
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC $ (392)                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (234)                  
U.S. Workers' Compensation (before discount)                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 8,589                  
2023 Prior Year Development Excluding the Impact of ADC (267)                  
Incurred Impact of ADC (4,301)                  
2023 (Net of Impact of ADC) 7,802                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 4,727                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 4,327                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 8,189                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (114)                  
Paid Impact of ADC $ (118)                  
Year 1 (as a percent) 11.90%                  
Year 2 (as a percent) 17.20%                  
Year 3 (as a percent) 11.00%                  
Year 4 (as a percent) 7.20%                  
Year 5 (as a percent) 4.80%                  
Year 6 (as a percent) 3.20%                  
Year 7 (as a percent) 2.00%                  
Year 8 (as a percent) 1.70%                  
Year 9 (as a percent) 1.50%                  
Year 10 (as a percent) 1.20%                  
U.S. Workers' Compensation (before discount) | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 118                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (3,632)                  
Unallocated loss adjustment expense prior year development 32                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 153                  
U.S. Workers' Compensation (before discount) | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,589 $ 1,614 $ 1,637 $ 1,679 $ 1,709 $ 1,794 $ 1,862 $ 1,866 $ 1,764 $ 1,729
2023 Prior Year Development Excluding the Impact of ADC (25)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 172                  
Cumulative Number of Reported Claims | country 41,529                  
Incurred Impact of ADC $ (349)                  
IBNR Impact of ADC (143)                  
2023 (Net of Impact of ADC) 1,240 1,243 1,171 1,223 1,329 1,309 1,310 1,311    
Total of IBNR Liabilities Net of Impact of ADC 29                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,226 1,207 1,180 1,137 1,096 1,030 930 786 558 231
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (3)                  
Paid Impact of ADC (64)                  
U.S. Workers' Compensation (before discount) | 2014 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (349) (371) (466) (456) (380) (485) (552) (555)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 22                  
U.S. Workers' Compensation (before discount) | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,592 1,612 1,634 1,675 1,722 1,814 1,866 1,864 1,708  
2023 Prior Year Development Excluding the Impact of ADC (20)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 355                  
Cumulative Number of Reported Claims | country 37,109                  
Incurred Impact of ADC $ (438)                  
IBNR Impact of ADC (228)                  
2023 (Net of Impact of ADC) 1,154 1,092 1,041 1,105 1,134 1,318 1,279 1,279    
Total of IBNR Liabilities Net of Impact of ADC 127                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,058 1,038 1,013 979 925 854 725 524 234  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 62                  
Paid Impact of ADC (54)                  
U.S. Workers' Compensation (before discount) | 2015 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (438) (520) (593) (570) (588) (496) (587) (585)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 82                  
U.S. Workers' Compensation (before discount) | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,025 1,036 1,075 1,090 1,140 1,318 1,346 1,299    
2023 Prior Year Development Excluding the Impact of ADC (11)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 224                  
Cumulative Number of Reported Claims | country 31,868                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,025 1,036 1,075 1,090 1,140 1,318 1,346 1,299    
Total of IBNR Liabilities Net of Impact of ADC 224                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 694 686 662 630 584 521 378 147    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (11)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2016 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0 0    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 705 712 731 763 776 850 789      
2023 Prior Year Development Excluding the Impact of ADC (7)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 218                  
Cumulative Number of Reported Claims | country 27,695                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 705 712 731 763 776 850 789      
Total of IBNR Liabilities Net of Impact of ADC 218                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 395 389 367 333 294 224 93      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (7)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2017 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 875 896 911 961 1,021 998        
2023 Prior Year Development Excluding the Impact of ADC (21)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 385                  
Cumulative Number of Reported Claims | country 22,222                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 875 896 911 961 1,021 998        
Total of IBNR Liabilities Net of Impact of ADC 385                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 409 388 359 296 215 85        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (21)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2018 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 788 801 812 873 887          
2023 Prior Year Development Excluding the Impact of ADC (13)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 285                  
Cumulative Number of Reported Claims | country 17,000                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 788 801 812 873 887          
Total of IBNR Liabilities Net of Impact of ADC 285                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 389 347 301 219 93          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (13)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2019 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 477 521 573 597            
2023 Prior Year Development Excluding the Impact of ADC (44)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 106                  
Cumulative Number of Reported Claims | country 13,839                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 477 521 573 597            
Total of IBNR Liabilities Net of Impact of ADC 106                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 245 205 159 64            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (44)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2020 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 545 570 597              
2023 Prior Year Development Excluding the Impact of ADC (25)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 274                  
Cumulative Number of Reported Claims | country 10,982                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 545 570 597              
Total of IBNR Liabilities Net of Impact of ADC 274                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 171 128 60              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (25)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2021 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 493 523                
2023 Prior Year Development Excluding the Impact of ADC (30)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 296                  
Cumulative Number of Reported Claims | country 9,339                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 493 523                
Total of IBNR Liabilities Net of Impact of ADC 296                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 102 45                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (30)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2022 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 500                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 397                  
Cumulative Number of Reported Claims | country 7,359                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 500                  
Total of IBNR Liabilities Net of Impact of ADC 397                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 38                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a)                  
Paid Impact of ADC 0                  
U.S. Workers' Compensation (before discount) | 2023 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Workers' Compensation (before discount) | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC (196)                  
Incurred Impact of ADC (787)                  
2023 (Net of Impact of ADC) 7,802 7,394 6,911 6,612 6,287 5,793 4,724 3,889    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (92)                  
U.S. Workers' Compensation (before discount) | Short Duration Insurance Contracts Last Ten Accident Years | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (787) (891) (1,059) (1,026) (968) (981) (1,139) (1,140)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 104                  
U.S. Workers' Compensation (before discount) | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
U.S. Workers' Compensation (before discount) | Incurred Impact Of Adverse Development Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 118                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (3,632)                  
U.S. Workers' Compensation (before discount) | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (65)                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (48)                  
U.S. Workers' Compensation (before discount) | Short Duration Insurance Contracts Accident Years Prior To2012 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 17                  
U.S. Workers' Compensation (before discount) | Net Of Impact Of Adverse Development Reinsurance Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 4,609                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 695                  
Unallocated loss adjustment expense prior year development 26                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 3,888                  
U.S. Workers' Compensation (before discount) | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development (6)                  
U.S. Excess Casualty                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 8,084                  
2023 Prior Year Development Excluding the Impact of ADC (32)                  
Incurred Impact of ADC (2,083)                  
2023 (Net of Impact of ADC) 7,238                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 4,724                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 2,044                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 5,404                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 18                  
Paid Impact of ADC $ (251)                  
Year 1 (as a percent) 1.20%                  
Year 2 (as a percent) 8.50%                  
Year 3 (as a percent) 9.20%                  
Year 4 (as a percent) 18.10%                  
Year 5 (as a percent) 10.50%                  
Year 6 (as a percent) 7.90%                  
Year 7 (as a percent) 7.40%                  
Year 8 (as a percent) 6.60%                  
Year 9 (as a percent) 2.70%                  
Year 10 (as a percent) 1.90%                  
U.S. Excess Casualty | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 251                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (1,488)                  
Unallocated loss adjustment expense prior year development 30                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 50                  
U.S. Excess Casualty | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,245 1,259 1,269 1,248 1,283 1,339 1,260 1,275 1,069 938
2023 Prior Year Development Excluding the Impact of ADC (14)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 277                  
Cumulative Number of Reported Claims | country 2,985                  
Incurred Impact of ADC $ (384)                  
IBNR Impact of ADC (144)                  
2023 (Net of Impact of ADC) 861 869 949 912 844 915 905 902    
Total of IBNR Liabilities Net of Impact of ADC 133                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 902 878 839 815 703 590 444 240 77 3
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (8)                  
Paid Impact of ADC (80)                  
U.S. Excess Casualty | 2014 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (384) (390) (320) (336) (439) (424) (355) (373)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 6                  
U.S. Excess Casualty | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,658 1,686 1,721 1,694 1,656 1,603 1,440 1,463 989  
2023 Prior Year Development Excluding the Impact of ADC (28)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 258                  
Cumulative Number of Reported Claims | country 3,142                  
Incurred Impact of ADC $ (462)                  
IBNR Impact of ADC (116)                  
2023 (Net of Impact of ADC) 1,196 1,174 1,231 1,211 1,163 1,139 1,015 1,027    
Total of IBNR Liabilities Net of Impact of ADC 142                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,291 1,253 1,124 1,061 935 718 391 210 9  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 22                  
Paid Impact of ADC (171)                  
U.S. Excess Casualty | 2015 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (462) (512) (490) (483) (493) (464) (425) (436)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 50                  
U.S. Excess Casualty | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,276 1,263 1,250 1,274 1,171 1,162 1,146 898    
2023 Prior Year Development Excluding the Impact of ADC 13                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 314                  
Cumulative Number of Reported Claims | country 2,813                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,276 1,263 1,250 1,274 1,171 1,162 1,146 898    
Total of IBNR Liabilities Net of Impact of ADC 314                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 798 670 566 502 388 204 80 28    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 13                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2016 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0 0    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,182 1,200 1,157 1,153 1,097 1,002 856      
2023 Prior Year Development Excluding the Impact of ADC (18)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 264                  
Cumulative Number of Reported Claims | country 2,079                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,182 1,200 1,157 1,153 1,097 1,002 856      
Total of IBNR Liabilities Net of Impact of ADC 264                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 781 676 585 505 156 45 1      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (18)                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2017 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 779 769 769 721 646 648        
2023 Prior Year Development Excluding the Impact of ADC 10                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 155                  
Cumulative Number of Reported Claims | country 1,461                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 779 769 769 721 646 648        
Total of IBNR Liabilities Net of Impact of ADC 155                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 494 414 315 227 125 1        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 10                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2018 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 600 612 597 583 577          
2023 Prior Year Development Excluding the Impact of ADC (12)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 301                  
Cumulative Number of Reported Claims | country 1,347                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 600 612 597 583 577          
Total of IBNR Liabilities Net of Impact of ADC 301                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 216 157 79 43 7          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (12)                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2019 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 420 410 413 406            
2023 Prior Year Development Excluding the Impact of ADC 10                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 238                  
Cumulative Number of Reported Claims | country 1,284                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 420 410 413 406            
Total of IBNR Liabilities Net of Impact of ADC 238                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 128 33 15 4            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 10                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2020 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 274 277 278              
2023 Prior Year Development Excluding the Impact of ADC (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 100                  
Cumulative Number of Reported Claims | country 855                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 274 277 278              
Total of IBNR Liabilities Net of Impact of ADC 100                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 62 43 4              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (3)                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2021 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 305 305                
2023 Prior Year Development Excluding the Impact of ADC 0                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 189                  
Cumulative Number of Reported Claims | country 490                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 305 305                
Total of IBNR Liabilities Net of Impact of ADC 189                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 51 14                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2022 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 345                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 326                  
Cumulative Number of Reported Claims | country 303                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 345                  
Total of IBNR Liabilities Net of Impact of ADC 326                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a)                  
Paid Impact of ADC 0                  
U.S. Excess Casualty | 2023 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Excess Casualty | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC (42)                  
Incurred Impact of ADC (846)                  
2023 (Net of Impact of ADC) 7,238 6,879 6,644 6,260 5,498 4,866 3,922 2,827    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 14                  
U.S. Excess Casualty | Short Duration Insurance Contracts Last Ten Accident Years | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (846) (902) (810) (819) (932) (888) (780) (809)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 56                  
U.S. Excess Casualty | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
U.S. Excess Casualty | Incurred Impact Of Adverse Development Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 251                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (1,488)                  
U.S. Excess Casualty | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (75)                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (111)                  
U.S. Excess Casualty | Short Duration Insurance Contracts Accident Years Prior To2012 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (36)                  
U.S. Excess Casualty | Net Of Impact Of Adverse Development Reinsurance Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below (4,473)                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 556                  
Unallocated loss adjustment expense prior year development 115                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 3,321                  
U.S. Excess Casualty | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development 85                  
U.S. Other Casualty                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 10,583                  
2023 Prior Year Development Excluding the Impact of ADC (133)                  
Incurred Impact of ADC (1,251)                  
2023 (Net of Impact of ADC) 10,087                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 6,668                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 1,448                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 5,363                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (133)                  
Paid Impact of ADC $ (298)                  
Year 1 (as a percent) 5.80%                  
Year 2 (as a percent) 11.30%                  
Year 3 (as a percent) 14.20%                  
Year 4 (as a percent) 14.40%                  
Year 5 (as a percent) 13.70%                  
Year 6 (as a percent) 9.40%                  
Year 7 (as a percent) 6.70%                  
Year 8 (as a percent) 4.00%                  
Year 9 (as a percent) 2.80%                  
Year 10 (as a percent) 0.50%                  
U.S. Other Casualty | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 298                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (1,053)                  
Unallocated loss adjustment expense prior year development 24                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,905 1,944 1,935 1,946 1,916 1,910 2,009 1,963 1,721 1,751
2023 Prior Year Development Excluding the Impact of ADC (39)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 46                  
Cumulative Number of Reported Claims | country 38,546                  
Incurred Impact of ADC $ (214)                  
IBNR Impact of ADC (29)                  
2023 (Net of Impact of ADC) 1,691 1,718 1,722 1,701 1,694 1,634 1,678 1,667    
Total of IBNR Liabilities Net of Impact of ADC 17                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,805 1,795 1,719 1,653 1,572 1,392 1,150 868 620 210
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (27)                  
Paid Impact of ADC (122)                  
U.S. Other Casualty | 2014 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (214) (226) (213) (245) (222) (276) (331) (296)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 12                  
U.S. Other Casualty | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,796 1,815 1,824 1,834 1,794 1,736 1,829 1,762 1,329  
2023 Prior Year Development Excluding the Impact of ADC (19)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 23                  
Cumulative Number of Reported Claims | country 35,754                  
Incurred Impact of ADC $ (282)                  
IBNR Impact of ADC (8)                  
2023 (Net of Impact of ADC) 1,514 1,563 1,562 1,553 1,493 1,423 1,373 1,361    
Total of IBNR Liabilities Net of Impact of ADC 15                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,707 1,680 1,603 1,485 1,351 1,087 769 309 105  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (49)                  
Paid Impact of ADC (176)                  
U.S. Other Casualty | 2015 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (282) (252) (262) (281) (301) (313) (456) (401)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (30)                  
U.S. Other Casualty | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,297 1,293 1,323 1,340 1,391 1,321 1,343 1,339    
2023 Prior Year Development Excluding the Impact of ADC 4                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 162                  
Cumulative Number of Reported Claims | country 29,191                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,297 1,293 1,323 1,340 1,391 1,321 1,343 1,339    
Total of IBNR Liabilities Net of Impact of ADC 162                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,074 1,018 938 846 703 489 298 77    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 4                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2016 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0 0    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 654 643 668 674 738 629 602      
2023 Prior Year Development Excluding the Impact of ADC 11                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 21                  
Cumulative Number of Reported Claims | country 21,266                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 654 643 668 674 738 629 602      
Total of IBNR Liabilities Net of Impact of ADC 21                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 592 527 455 314 216 111 51      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 11                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2017 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 810 824 870 837 845 802        
2023 Prior Year Development Excluding the Impact of ADC (14)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 148                  
Cumulative Number of Reported Claims | country 16,967                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 810 824 870 837 845 802        
Total of IBNR Liabilities Net of Impact of ADC 148                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 565 470 360 227 122 43        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (14)                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2018 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,039 1,062 1,053 1,058 1,059          
2023 Prior Year Development Excluding the Impact of ADC (23)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 526                  
Cumulative Number of Reported Claims | country 21,036                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,039 1,062 1,053 1,058 1,059          
Total of IBNR Liabilities Net of Impact of ADC 526                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 410 321 226 138 53          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (23)                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2019 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 540 538 576 524            
2023 Prior Year Development Excluding the Impact of ADC 2                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 277                  
Cumulative Number of Reported Claims | country 11,318                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 540 538 576 524            
Total of IBNR Liabilities Net of Impact of ADC 277                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 198 139 73 26            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 2                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2020 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 790 793 795              
2023 Prior Year Development Excluding the Impact of ADC (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 519                  
Cumulative Number of Reported Claims | country 10,572                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 790 793 795              
Total of IBNR Liabilities Net of Impact of ADC 519                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 169 87 32              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (3)                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2021 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 819 793                
2023 Prior Year Development Excluding the Impact of ADC 26                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 617                  
Cumulative Number of Reported Claims | country 12,457                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 819 793                
Total of IBNR Liabilities Net of Impact of ADC 617                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 112 38                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 26                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2022 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 933                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 848                  
Cumulative Number of Reported Claims | country 10,401                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 933                  
Total of IBNR Liabilities Net of Impact of ADC 848                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 36                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a)                  
Paid Impact of ADC 0                  
U.S. Other Casualty | 2023 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Other Casualty | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC (55)                  
Incurred Impact of ADC (496)                  
2023 (Net of Impact of ADC) 10,087 9,227 8,569 7,687 7,220 5,809 4,996 4,367    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (73)                  
U.S. Other Casualty | Short Duration Insurance Contracts Last Ten Accident Years | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (496) (478) (475) (526) (523) (589) (787) (697)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (18)                  
U.S. Other Casualty | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
U.S. Other Casualty | Incurred Impact Of Adverse Development Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 298                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (1,053)                  
U.S. Other Casualty | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (67)                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (73)                  
U.S. Other Casualty | Short Duration Insurance Contracts Accident Years Prior To2012 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (6)                  
U.S. Other Casualty | Net Of Impact Of Adverse Development Reinsurance Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below (6,370)                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 395                  
Unallocated loss adjustment expense prior year development 13                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 4,112                  
U.S. Other Casualty | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development (11)                  
U.S. Financial Lines                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 17,560                  
2023 Prior Year Development Excluding the Impact of ADC 94                  
Incurred Impact of ADC (514)                  
2023 (Net of Impact of ADC) 16,768                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 11,645                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 271                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 6,186                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 50                  
Paid Impact of ADC $ (501)                  
Year 1 (as a percent) 3.70%                  
Year 2 (as a percent) 14.60%                  
Year 3 (as a percent) 18.20%                  
Year 4 (as a percent) 15.60%                  
Year 5 (as a percent) 12.50%                  
Year 6 (as a percent) 8.10%                  
Year 7 (as a percent) 6.10%                  
Year 8 (as a percent) 5.80%                  
Year 9 (as a percent) 3.90%                  
Year 10 (as a percent) 1.40%                  
U.S. Financial Lines | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 501                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (223)                  
Unallocated loss adjustment expense prior year development 4                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (44)                  
U.S. Financial Lines | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,017 2,014 2,057 2,000 1,981 1,960 1,927 1,892 1,777 1,812
2023 Prior Year Development Excluding the Impact of ADC 3                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 91                  
Cumulative Number of Reported Claims | country 17,650                  
Incurred Impact of ADC $ (297)                  
IBNR Impact of ADC (68)                  
2023 (Net of Impact of ADC) 1,720 1,738 1,761 1,759 1,741 1,753 1,729 1,733    
Total of IBNR Liabilities Net of Impact of ADC 23                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,849 1,820 1,758 1,658 1,573 1,387 1,158 849 366 66
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (18)                  
Paid Impact of ADC (147)                  
U.S. Financial Lines | 2014 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (297) (276) (296) (241) (240) (207) (198) (159)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (21)                  
U.S. Financial Lines | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,048 2,044 1,959 1,874 1,830 1,788 1,743 1,762 1,737  
2023 Prior Year Development Excluding the Impact of ADC 4                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 78                  
Cumulative Number of Reported Claims | country 16,253                  
Incurred Impact of ADC $ (495)                  
IBNR Impact of ADC (63)                  
2023 (Net of Impact of ADC) 1,553 1,605 1,595 1,550 1,552 1,462 1,430 1,429    
Total of IBNR Liabilities Net of Impact of ADC 15                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,914 1,818 1,686 1,488 1,282 1,055 791 390 63  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (52)                  
Paid Impact of ADC (354)                  
U.S. Financial Lines | 2015 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (495) (439) (364) (324) (278) (326) (313) (333)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (56)                  
U.S. Financial Lines | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,308 2,325 2,281 2,139 2,064 1,993 1,855 1,605    
2023 Prior Year Development Excluding the Impact of ADC (17)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 133                  
Cumulative Number of Reported Claims | country 16,127                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 2,308 2,325 2,281 2,139 2,064 1,993 1,855 1,605    
Total of IBNR Liabilities Net of Impact of ADC 133                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,039 1,903 1,826 1,659 1,358 1,002 499 73    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (17)                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2016 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0 0    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,957 1,987 1,898 1,846 1,756 1,675 1,564      
2023 Prior Year Development Excluding the Impact of ADC (30)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 130                  
Cumulative Number of Reported Claims | country 15,269                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,957 1,987 1,898 1,846 1,756 1,675 1,564      
Total of IBNR Liabilities Net of Impact of ADC 130                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,653 1,515 1,396 1,118 761 391 64      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (30)                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2017 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,322 2,225 2,063 1,882 1,766 1,640        
2023 Prior Year Development Excluding the Impact of ADC 97                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 498                  
Cumulative Number of Reported Claims | country 14,833                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 2,322 2,225 2,063 1,882 1,766 1,640        
Total of IBNR Liabilities Net of Impact of ADC 498                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,601 1,415 1,126 835 486 86        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 97                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2018 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,912 1,926 1,627 1,536 1,503          
2023 Prior Year Development Excluding the Impact of ADC (14)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 513                  
Cumulative Number of Reported Claims | country 13,319                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,912 1,926 1,627 1,536 1,503          
Total of IBNR Liabilities Net of Impact of ADC 513                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,204 953 642 367 94          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (14)                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2019 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,457 1,408 1,252 1,213            
2023 Prior Year Development Excluding the Impact of ADC 49                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 331                  
Cumulative Number of Reported Claims | country 10,390                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,457 1,408 1,252 1,213            
Total of IBNR Liabilities Net of Impact of ADC 331                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 915 648 356 84            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 49                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2020 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,388 1,408 1,430              
2023 Prior Year Development Excluding the Impact of ADC (20)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 894                  
Cumulative Number of Reported Claims | country 7,117                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,388 1,408 1,430              
Total of IBNR Liabilities Net of Impact of ADC 894                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 315 151 43              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (20)                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2021 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,108 1,130                
2023 Prior Year Development Excluding the Impact of ADC (22)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 948                  
Cumulative Number of Reported Claims | country 5,809                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,108 1,130                
Total of IBNR Liabilities Net of Impact of ADC 948                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 109 30                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (22)                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2022 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,043                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 950                  
Cumulative Number of Reported Claims | country 6,467                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,043                  
Total of IBNR Liabilities Net of Impact of ADC 950                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 46                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a)                  
Paid Impact of ADC 0                  
U.S. Financial Lines | 2023 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Financial Lines | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC 50                  
Incurred Impact of ADC (792)                  
2023 (Net of Impact of ADC) 16,768 15,752 13,907 11,925 10,382 8,523 6,578 4,767    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (27)                  
U.S. Financial Lines | Short Duration Insurance Contracts Last Ten Accident Years | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (792) (715) (660) (565) (518) (533) (511) (492)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (77)                  
U.S. Financial Lines | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
U.S. Financial Lines | Incurred Impact Of Adverse Development Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 501                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (223)                  
U.S. Financial Lines | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 27                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 56                  
U.S. Financial Lines | Short Duration Insurance Contracts Accident Years Prior To2012 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 29                  
U.S. Financial Lines | Net Of Impact Of Adverse Development Reinsurance Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below (11,144)                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 48                  
Unallocated loss adjustment expense prior year development 21                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 5,672                  
U.S. Financial Lines | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development 17                  
U.S. Property and Special Risks                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 28,412                  
2023 Prior Year Development Excluding the Impact of ADC (10)                  
Incurred Impact of ADC (211)                  
2023 (Net of Impact of ADC) 28,260                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 24,207                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 409                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 4,614                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
Paid Impact of ADC $ (87)                  
Year 1 (as a percent) 35.20%                  
Year 2 (as a percent) 32.20%                  
Year 3 (as a percent) 11.80%                  
Year 4 (as a percent) 8.10%                  
Year 5 (as a percent) 4.90%                  
Year 6 (as a percent) 3.10%                  
Year 7 (as a percent) 1.80%                  
Year 8 (as a percent) 1.30%                  
Year 9 (as a percent) 1.50%                  
Year 10 (as a percent) 2.30%                  
U.S. Property and Special Risks | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 87                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (146)                  
Unallocated loss adjustment expense prior year development 1                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 10                  
U.S. Property and Special Risks | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,437 2,440 2,446 2,460 2,477 2,494 2,480 2,490 2,396 2,600
2023 Prior Year Development Excluding the Impact of ADC (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 4                  
Cumulative Number of Reported Claims | country 60,766                  
Incurred Impact of ADC $ (52)                  
IBNR Impact of ADC (2)                  
2023 (Net of Impact of ADC) 2,385 2,364 2,376 2,382 2,401 2,430 2,419 2,423    
Total of IBNR Liabilities Net of Impact of ADC 2                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,418 2,362 2,352 2,329 2,293 2,207 2,073 1,869 1,545 795
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 21                  
Paid Impact of ADC (20)                  
U.S. Property and Special Risks | 2014 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (52) (76) (70) (78) (76) (64) (61) (67)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 24                  
U.S. Property and Special Risks | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,493 2,490 2,479 2,471 2,466 2,492 2,489 2,506 2,567  
2023 Prior Year Development Excluding the Impact of ADC 3                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 4                  
Cumulative Number of Reported Claims | country 59,513                  
Incurred Impact of ADC $ (100)                  
IBNR Impact of ADC (1)                  
2023 (Net of Impact of ADC) 2,393 2,375 2,372 2,372 2,372 2,405 2,391 2,365    
Total of IBNR Liabilities Net of Impact of ADC 3                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,457 2,391 2,344 2,308 2,240 2,121 1,878 1,572 844  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 18                  
Paid Impact of ADC (67)                  
U.S. Property and Special Risks | 2015 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (100) (115) (107) (99) (94) (87) (98) (141)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 15                  
U.S. Property and Special Risks | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,713 2,700 2,694 2,707 2,697 2,690 2,748 2,674    
2023 Prior Year Development Excluding the Impact of ADC 13                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 8                  
Cumulative Number of Reported Claims | country 54,821                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 2,713 2,700 2,694 2,707 2,697 2,690 2,748 2,674    
Total of IBNR Liabilities Net of Impact of ADC 8                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,647 2,616 2,539 2,464 2,296 2,076 1,747 821    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 13                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2016 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0 0    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 4,175 4,212 4,173 4,153 4,127 4,239 4,673      
2023 Prior Year Development Excluding the Impact of ADC (37)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 15                  
Cumulative Number of Reported Claims | country 79,764                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 4,175 4,212 4,173 4,153 4,127 4,239 4,673      
Total of IBNR Liabilities Net of Impact of ADC 15                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 4,055 3,999 3,897 3,638 3,281 2,625 1,137      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (37)                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2017 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 3,210 3,201 3,229 2,992 2,993 2,978        
2023 Prior Year Development Excluding the Impact of ADC 9                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 112                  
Cumulative Number of Reported Claims | country 69,922                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 3,210 3,201 3,229 2,992 2,993 2,978        
Total of IBNR Liabilities Net of Impact of ADC 112                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,994 2,863 2,715 2,509 2,162 977        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 9                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2018 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,177 2,222 2,211 2,146 2,177          
2023 Prior Year Development Excluding the Impact of ADC (45)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 25                  
Cumulative Number of Reported Claims | country 78,848                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 2,177 2,222 2,211 2,146 2,177          
Total of IBNR Liabilities Net of Impact of ADC 25                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,083 2,037 1,906 1,673 1,039          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (45)                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2019 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 3,238 3,280 3,320 3,391            
2023 Prior Year Development Excluding the Impact of ADC (42)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 761                  
Cumulative Number of Reported Claims | country 68,644                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 3,238 3,280 3,320 3,391            
Total of IBNR Liabilities Net of Impact of ADC 761                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,190 1,874 1,613 844            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (42)                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2020 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,160 2,213 2,339              
2023 Prior Year Development Excluding the Impact of ADC (53)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 101                  
Cumulative Number of Reported Claims | country 81,795                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 2,160 2,213 2,339              
Total of IBNR Liabilities Net of Impact of ADC 101                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,983 1,743 878              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (53)                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2021 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 3,281 3,171                
2023 Prior Year Development Excluding the Impact of ADC 110                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 690                  
Cumulative Number of Reported Claims | country 85,477                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 3,281 3,171                
Total of IBNR Liabilities Net of Impact of ADC 690                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 2,207 1,208                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 110                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2022 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,528                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 777                  
Cumulative Number of Reported Claims | country 88,129                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 2,528                  
Total of IBNR Liabilities Net of Impact of ADC 777                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,173                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a)                  
Paid Impact of ADC 0                  
U.S. Property and Special Risks | 2023 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Property and Special Risks | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC (45)                  
Incurred Impact of ADC (152)                  
2023 (Net of Impact of ADC) 28,260 25,738 22,714 20,143 16,767 14,742 12,231 7,462    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (6)                  
U.S. Property and Special Risks | Short Duration Insurance Contracts Last Ten Accident Years | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (152) (191) (177) (177) (170) (151) (159) (208)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 39                  
U.S. Property and Special Risks | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
U.S. Property and Special Risks | Incurred Impact Of Adverse Development Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 87                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (146)                  
U.S. Property and Special Risks | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 39                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 9                  
U.S. Property and Special Risks | Short Duration Insurance Contracts Accident Years Prior To2012 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (30)                  
U.S. Property and Special Risks | Net Of Impact Of Adverse Development Reinsurance Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below (24,120)                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 263                  
Unallocated loss adjustment expense prior year development (3)                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 4,403                  
U.S. Property and Special Risks | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development (4)                  
U.S. Personal Insurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 12,876                  
2023 Prior Year Development Excluding the Impact of ADC (64)                  
Incurred Impact of ADC (1)                  
2023 (Net of Impact of ADC) 12,860                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 12,060                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (48)                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 768                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (65)                  
Paid Impact of ADC $ (16)                  
Year 1 (as a percent) 61.60%                  
Year 2 (as a percent) 23.80%                  
Year 3 (as a percent) 5.20%                  
Year 4 (as a percent) 0.80%                  
Year 5 (as a percent) 2.40%                  
Year 6 (as a percent) 0.90%                  
Year 7 (as a percent) 0.50%                  
Year 8 (as a percent) 0.30%                  
Year 9 (as a percent) 0.30%                  
Year 10 (as a percent) 0.30%                  
U.S. Personal Insurance | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 16                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (1)                  
Unallocated loss adjustment expense prior year development 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (1)                  
U.S. Personal Insurance | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,592 1,592 1,587 1,588 1,584 1,583 1,572 1,572 1,562 1,552
2023 Prior Year Development Excluding the Impact of ADC 0                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 5                  
Cumulative Number of Reported Claims | country 275,132                  
Incurred Impact of ADC $ (8)                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,584 1,584 1,582 1,584 1,580 1,571 1,564 1,564    
Total of IBNR Liabilities Net of Impact of ADC 5                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,584 1,579 1,572 1,568 1,555 1,536 1,507 1,463 1,380 959
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
Paid Impact of ADC (8)                  
U.S. Personal Insurance | 2014 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (8) (8) (5) (4) (4) (12) (8) (8)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,487 1,488 1,487 1,485 1,482 1,483 1,494 1,498 1,511  
2023 Prior Year Development Excluding the Impact of ADC (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 8                  
Cumulative Number of Reported Claims | country 261,176                  
Incurred Impact of ADC $ (8)                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,479 1,481 1,482 1,480 1,476 1,472 1,475 1,476    
Total of IBNR Liabilities Net of Impact of ADC 8                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,471 1,468 1,463 1,461 1,455 1,439 1,411 1,320 931  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (2)                  
Paid Impact of ADC (8)                  
U.S. Personal Insurance | 2015 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (8) (7) (5) (5) (6) (11) (19) (22)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (1)                  
U.S. Personal Insurance | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,541 1,544 1,544 1,542 1,540 1,533 1,533 1,536    
2023 Prior Year Development Excluding the Impact of ADC (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 12                  
Cumulative Number of Reported Claims | country 247,479                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,541 1,544 1,544 1,542 1,540 1,533 1,533 1,536    
Total of IBNR Liabilities Net of Impact of ADC 12                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,521 1,518 1,512 1,501 1,460 1,422 1,344 857    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (3)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2016 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0 0    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,896 1,916 1,924 2,057 2,011 2,137 1,878      
2023 Prior Year Development Excluding the Impact of ADC (20)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 15                  
Cumulative Number of Reported Claims | country 220,038                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,896 1,916 1,924 2,057 2,011 2,137 1,878      
Total of IBNR Liabilities Net of Impact of ADC 15                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,861 1,852 1,826 1,789 1,896 1,672 941      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (20)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2017 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0 0      
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,920 1,936 1,937 2,154 2,193 2,188        
2023 Prior Year Development Excluding the Impact of ADC (16)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 33                  
Cumulative Number of Reported Claims | country 102,256                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,920 1,936 1,937 2,154 2,193 2,188        
Total of IBNR Liabilities Net of Impact of ADC 33                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,849 1,832 1,789 1,973 1,939 1,227        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (16)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2018 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0 0        
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,578 1,596 1,646 1,664 1,593          
2023 Prior Year Development Excluding the Impact of ADC (18)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 43                  
Cumulative Number of Reported Claims | country 93,428                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 1,578 1,596 1,646 1,664 1,593          
Total of IBNR Liabilities Net of Impact of ADC 43                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 1,491 1,416 1,379 1,295 884          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (18)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2019 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0 0          
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 894 913 906 954            
2023 Prior Year Development Excluding the Impact of ADC (19)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 51                  
Cumulative Number of Reported Claims | country 55,101                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 894 913 906 954            
Total of IBNR Liabilities Net of Impact of ADC 51                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 824 725 679 667            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (19)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2020 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0 0            
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 762 765 748              
2023 Prior Year Development Excluding the Impact of ADC (3)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 70                  
Cumulative Number of Reported Claims | country 56,234                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 762 765 748              
Total of IBNR Liabilities Net of Impact of ADC 70                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 658 650 488              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (3)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2021 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0 0              
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 529 517                
2023 Prior Year Development Excluding the Impact of ADC 12                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 93                  
Cumulative Number of Reported Claims | country 51,983                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 529 517                
Total of IBNR Liabilities Net of Impact of ADC 93                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 401 372                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 12                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2022 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0 0                
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 677                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 248                  
Cumulative Number of Reported Claims | country 32,022                  
Incurred Impact of ADC $ 0                  
IBNR Impact of ADC 0                  
2023 (Net of Impact of ADC) 677                  
Total of IBNR Liabilities Net of Impact of ADC 248                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 400                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a)                  
Paid Impact of ADC 0                  
U.S. Personal Insurance | 2023 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC 0                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC (68)                  
Incurred Impact of ADC (16)                  
2023 (Net of Impact of ADC) 12,860 12,252 11,769 11,435 10,393 8,901 6,450 4,576    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (69)                  
U.S. Personal Insurance | Short Duration Insurance Contracts Last Ten Accident Years | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred Impact of ADC (16) (15) (10) (9) (10) (23) (27) (30)    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) (1)                  
U.S. Personal Insurance | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
U.S. Personal Insurance | Incurred Impact Of Adverse Development Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 16                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (1)                  
U.S. Personal Insurance | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 4                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 4                  
U.S. Personal Insurance | Short Duration Insurance Contracts Accident Years Prior To2012 | Adverse Development Reinsurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Prior Year Development Net of External Reinsurance After ADC Cessions(a) 0                  
U.S. Personal Insurance | Net Of Impact Of Adverse Development Reinsurance Cover                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below (12,044)                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (49)                  
Unallocated loss adjustment expense prior year development 0                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 767                  
U.S. Personal Insurance | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development 0                  
UK/Europe Casualty and Financial lines                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 13,695                  
2023 Prior Year Development Excluding the Impact of ADC 165                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 7,109                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 861                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 7,447                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) $ 165                  
Year 1 (as a percent) 5.60%                  
Year 2 (as a percent) 14.30%                  
Year 3 (as a percent) 12.20%                  
Year 4 (as a percent) 11.30%                  
Year 5 (as a percent) 9.30%                  
Year 6 (as a percent) 10.30%                  
Year 7 (as a percent) 6.10%                  
Year 8 (as a percent) 4.90%                  
Year 9 (as a percent) 3.70%                  
Year 10 (as a percent) 2.10%                  
UK/Europe Casualty and Financial lines | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance $ 1,117 1,111 1,106 1,064 1,122 1,034 1,039 1,032 1,009 1,036
2023 Prior Year Development Excluding the Impact of ADC 6                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 75                  
Cumulative Number of Reported Claims | country 102,063                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 883 859 818 757 695 629 529 409 258 72
UK/Europe Casualty and Financial lines | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,266 1,258 1,238 1,234 1,244 1,170 1,262 1,233 1,092  
2023 Prior Year Development Excluding the Impact of ADC 8                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 74                  
Cumulative Number of Reported Claims | country 113,865                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,041 994 949 859 683 568 433 240 71  
UK/Europe Casualty and Financial lines | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,613 1,610 1,597 1,601 1,498 1,497 1,453 1,314    
2023 Prior Year Development Excluding the Impact of ADC 3                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 100                  
Cumulative Number of Reported Claims | country 142,721                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,260 1,168 1,059 930 775 586 379 119    
UK/Europe Casualty and Financial lines | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,408 1,366 1,381 1,321 1,252 1,323 1,343      
2023 Prior Year Development Excluding the Impact of ADC 42                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 177                  
Cumulative Number of Reported Claims | country 149,665                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 964 896 753 602 447 280 96      
UK/Europe Casualty and Financial lines | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,664 1,619 1,521 1,482 1,415 1,343        
2023 Prior Year Development Excluding the Impact of ADC 45                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 245                  
Cumulative Number of Reported Claims | country 151,467                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,128 903 742 572 374 113        
UK/Europe Casualty and Financial lines | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,345 1,351 1,334 1,262 1,005          
2023 Prior Year Development Excluding the Impact of ADC (6)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 292                  
Cumulative Number of Reported Claims | country 142,426                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 760 658 478 310 98          
UK/Europe Casualty and Financial lines | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,202 1,216 1,271 1,219            
2023 Prior Year Development Excluding the Impact of ADC (14)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 474                  
Cumulative Number of Reported Claims | country 85,762                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 507 367 228 60            
UK/Europe Casualty and Financial lines | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,347 1,335 1,375              
2023 Prior Year Development Excluding the Impact of ADC 12                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 723                  
Cumulative Number of Reported Claims | country 76,503                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 345 233 51              
UK/Europe Casualty and Financial lines | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,261 1,300                
2023 Prior Year Development Excluding the Impact of ADC (39)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 894                  
Cumulative Number of Reported Claims | country 71,630                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 185 57                
UK/Europe Casualty and Financial lines | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,472                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1,100                  
Cumulative Number of Reported Claims | country 57,306                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 36                  
UK/Europe Casualty and Financial lines | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC 57                  
UK/Europe Casualty and Financial lines | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
UK/Europe Casualty and Financial lines | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 108                  
UK/Europe Casualty and Financial lines | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development 0                  
UK/Europe Property and Special Risks                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 13,306                  
2023 Prior Year Development Excluding the Impact of ADC 81                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 10,479                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 86                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 2,913                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) $ 81                  
Year 1 (as a percent) 21.10%                  
Year 2 (as a percent) 38.70%                  
Year 3 (as a percent) 16.70%                  
Year 4 (as a percent) 7.70%                  
Year 5 (as a percent) 2.70%                  
Year 6 (as a percent) 2.10%                  
Year 7 (as a percent) 0.80%                  
Year 8 (as a percent) 0.20%                  
Year 9 (as a percent) 0.30%                  
Year 10 (as a percent) 0.30%                  
UK/Europe Property and Special Risks | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance $ 1,349 1,360 1,382 1,387 1,426 1,450 1,460 1,431 1,470 1,439
2023 Prior Year Development Excluding the Impact of ADC (11)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ (2)                  
Cumulative Number of Reported Claims | country 48,030                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,354 1,350 1,342 1,329 1,320 1,293 1,255 1,187 912 311
UK/Europe Property and Special Risks | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,442 1,455 1,421 1,434 1,444 1,463 1,531 1,469 1,552  
2023 Prior Year Development Excluding the Impact of ADC (13)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 7                  
Cumulative Number of Reported Claims | country 54,639                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,362 1,363 1,362 1,354 1,331 1,295 1,193 920 346  
UK/Europe Property and Special Risks | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,604 1,609 1,674 1,678 1,682 1,678 1,685 1,536    
2023 Prior Year Development Excluding the Impact of ADC (5)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 10                  
Cumulative Number of Reported Claims | country 57,287                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,585 1,591 1,574 1,545 1,500 1,367 1,114 456    
UK/Europe Property and Special Risks | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,565 1,566 1,600 1,616 1,609 1,614 1,649      
2023 Prior Year Development Excluding the Impact of ADC (1)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 12                  
Cumulative Number of Reported Claims | country 53,411                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,472 1,459 1,420 1,364 1,222 940 353      
UK/Europe Property and Special Risks | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,463 1,468 1,520 1,533 1,555 1,505        
2023 Prior Year Development Excluding the Impact of ADC (5)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 8                  
Cumulative Number of Reported Claims | country 44,183                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,339 1,303 1,289 1,161 978 316        
UK/Europe Property and Special Risks | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,086 1,090 1,101 1,100 1,138          
2023 Prior Year Development Excluding the Impact of ADC (4)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 39                  
Cumulative Number of Reported Claims | country 33,637                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 944 907 820 649 264          
UK/Europe Property and Special Risks | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,218 1,200 1,241 1,301            
2023 Prior Year Development Excluding the Impact of ADC 18                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 136                  
Cumulative Number of Reported Claims | country 25,822                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 912 819 668 249            
UK/Europe Property and Special Risks | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 932 982 1,019              
2023 Prior Year Development Excluding the Impact of ADC (50)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 64                  
Cumulative Number of Reported Claims | country 22,306                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 691 504 189              
UK/Europe Property and Special Risks | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,288 1,123                
2023 Prior Year Development Excluding the Impact of ADC 165                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 220                  
Cumulative Number of Reported Claims | country 23,295                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 661 194                
UK/Europe Property and Special Risks | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,359                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 539                  
Cumulative Number of Reported Claims | country 15,946                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 159                  
UK/Europe Property and Special Risks | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC 94                  
UK/Europe Property and Special Risks | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
UK/Europe Property and Special Risks | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance (13)                  
UK/Europe Property and Special Risks | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development 0                  
UK/Europe and Japan Personal Insurance                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 20,193                  
2023 Prior Year Development Excluding the Impact of ADC (57)                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 18,747                  
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 37                  
Liabilities for losses and loss adjustment expenses and prior year loss development, net of reinsurance 1,483                  
Prior Year Development Net of External Reinsurance After ADC Cessions(a) $ (57)                  
Year 1 (as a percent) 57.90%                  
Year 2 (as a percent) 26.20%                  
Year 3 (as a percent) 7.20%                  
Year 4 (as a percent) 3.60%                  
Year 5 (as a percent) 1.80%                  
Year 6 (as a percent) 1.30%                  
Year 7 (as a percent) 0.50%                  
Year 8 (as a percent) 0.40%                  
Year 9 (as a percent) 0.30%                  
Year 10 (as a percent) 0.20%                  
UK/Europe and Japan Personal Insurance | 2014                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance $ 2,224 2,220 2,197 2,199 2,197 2,197 2,204 2,207 2,220 2,210
2023 Prior Year Development Excluding the Impact of ADC 4                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 2                  
Cumulative Number of Reported Claims | country 1,799,271                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 2,189 2,184 2,179 2,170 2,158 2,137 2,090 1,999 1,817 $ 1,198
UK/Europe and Japan Personal Insurance | 2015                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,257 2,254 2,256 2,255 2,255 2,257 2,265 2,264 2,284  
2023 Prior Year Development Excluding the Impact of ADC 3                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 0                  
Cumulative Number of Reported Claims | country 1,777,699                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 2,244 2,234 2,226 2,209 2,183 2,146 2,046 1,861 $ 1,228  
UK/Europe and Japan Personal Insurance | 2016                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,212 2,209 2,216 2,219 2,221 2,226 2,240 2,241    
2023 Prior Year Development Excluding the Impact of ADC 3                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 1                  
Cumulative Number of Reported Claims | country 1,794,987                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 2,195 2,187 2,173 2,147 2,102 2,013 1,830 $ 1,225    
UK/Europe and Japan Personal Insurance | 2017                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,108 2,100 2,115 2,099 2,103 2,118 2,196      
2023 Prior Year Development Excluding the Impact of ADC 8                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 0                  
Cumulative Number of Reported Claims | country 1,718,502                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 2,077 2,078 2,056 2,020 1,950 1,791 $ 1,200      
UK/Europe and Japan Personal Insurance | 2018                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,448 2,450 2,431 2,458 2,461 2,555        
2023 Prior Year Development Excluding the Impact of ADC (2)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 4                  
Cumulative Number of Reported Claims | country 1,915,683                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 2,404 2,352 2,309 2,225 2,063 $ 1,520        
UK/Europe and Japan Personal Insurance | 2019                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 2,002 2,000 2,015 2,050 2,085          
2023 Prior Year Development Excluding the Impact of ADC 2                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 3                  
Cumulative Number of Reported Claims | country 1,673,976                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,950 1,916 1,854 1,726 $ 1,219          
UK/Europe and Japan Personal Insurance | 2020                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,701 1,713 1,771 1,909            
2023 Prior Year Development Excluding the Impact of ADC (12)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 19                  
Cumulative Number of Reported Claims | country 1,389,704                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,619 1,576 1,470 $ 1,020            
UK/Europe and Japan Personal Insurance | 2021                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,689 1,719 1,776              
2023 Prior Year Development Excluding the Impact of ADC (30)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 32                  
Cumulative Number of Reported Claims | country 1,387,230                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,533 1,423 $ 1,003              
UK/Europe and Japan Personal Insurance | 2022                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,854 1,889                
2023 Prior Year Development Excluding the Impact of ADC (35)                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 89                  
Cumulative Number of Reported Claims | country 2,050,657                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 1,572 $ 1,100                
UK/Europe and Japan Personal Insurance | 2023                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Incurred losses and allocated loss adjustment expenses, undiscounted and net of reinsurance 1,698                  
2023 Prior Year Development Excluding the Impact of ADC                  
Total of IBNR Liabilities Plus Expected Development on Reported Losses $ 256                  
Cumulative Number of Reported Claims | country 1,275,686                  
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below $ 964                  
UK/Europe and Japan Personal Insurance | Short Duration Insurance Contracts Last Ten Accident Years                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
2023 Prior Year Development Excluding the Impact of ADC (59)                  
UK/Europe and Japan Personal Insurance | Shortduration Insurance Contracts Accident Years Prior To Current Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Cumulative Paid Losses and Allocated Loss Adjustment Expenses, Net of Reinsurance from the table below 0                  
UK/Europe and Japan Personal Insurance | Short Duration Insurance Contracts Accident Years Prior To2012                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Liabilities for losses and loss adjustment expenses and prior year development before accident year 2014, net of reinsurance 2                  
UK/Europe and Japan Personal Insurance | Unallocated To Accident Year                    
Liability for Claims and Claims Adjustment Expense [Line Items]                    
Unallocated loss adjustment expense prior year development $ 0