v3.26.1
Acquisitions - Narrative (Details)
shares in Thousands, £ in Millions, $ in Millions
1 Months Ended 3 Months Ended
Jan. 27, 2026
USD ($)
shares
Dec. 10, 2025
GBP (£)
May 02, 2025
USD ($)
Dec. 31, 2025
USD ($)
Mar. 31, 2026
USD ($)
shares
Mar. 31, 2025
USD ($)
Business Combination [Line Items]            
Acquisitions, cash payment         $ 9 $ 1
Preliminary values of intangible assets         185  
Customer Relationships [Member]            
Business Combination [Line Items]            
Preliminary values of intangible assets         $ 132  
Newfront Insurance Holdings, Inc            
Business Combination [Line Items]            
Acquisitions, cash payment $ 900          
Acquisiiton , equity payment 150          
Newfront Insurance Holdings, Inc | Customer Relationships [Member]            
Business Combination [Line Items]            
Preliminary values of intangible assets $ 131          
Weighted-average expected lives of intangible assets 13 years          
Newfront Insurance Holdings, Inc | Developed Software [Member]            
Business Combination [Line Items]            
Preliminary values of intangible assets $ 53          
Weighted-average expected lives of intangible assets 7 years          
Newfront Insurance Holdings, Inc | Performance Targets            
Business Combination [Line Items]            
Contingent consideration, amount $ 250          
Newfront Insurance Holdings, Inc | Restricted Stock Units [Member]            
Business Combination [Line Items]            
Number of shares issued | shares 187       187  
Newfront Insurance Holdings, Inc | Restricted Stock Awards [Member]            
Business Combination [Line Items]            
Number of shares issued | shares 225       225  
Number of ordinary shares vested | shares 199          
Newfront Insurance Holdings, Inc | Senior Notes            
Business Combination [Line Items]            
Proceeds from debt, net of issuance costs       $ 1,000    
Newfront Insurance Holdings, Inc | Up-Front            
Business Combination [Line Items]            
Contingent consideration fair value $ 1,050          
Pending Acquisitions | Cushon            
Business Combination [Line Items]            
Acquisitions, cash payment | £   £ 150        
Contingent consideration, amount | £   £ 100        
Pending Acquisitions | Al-Futtaim Willis            
Business Combination [Line Items]            
Acquisitions, cash payment     $ 58      
Reamining controlling interest     51.00%      
Equity Based Payment | Newfront Insurance Holdings, Inc | Above Target Performance            
Business Combination [Line Items]            
Contingent consideration, amount $ 150