v3.24.2
Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2024
Jun. 30, 2023
Jun. 30, 2024
Jun. 30, 2023
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax $ 2,219 $ 2,118 $ 4,514 $ 4,321
Reimbursable expenses and other [1] 20 22 40 50
Interest and other income 46 41 92 82
Total revenue 2,265 2,159 4,606 4,403
HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 1,266 1,224 2,610 2,520
Reimbursable expenses and other [1] 15 18 32 33
Interest and other income 9 9 18 15
Total revenue 1,275 1,233 2,628 2,535
R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 951 886 1,901 1,774
Reimbursable expenses and other [1] 3 3 6 6
Interest and other income 31 17 62 36
Total revenue 982 903 1,963 1,810
Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 2 [1] 8 [1] 3 27
Reimbursable expenses and other [1] 2 1 2 11
Interest and other income 6 [1] 15 [1] 12 31
Total revenue 8 [1] 23 [1] 15 58
Broking [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 1,057 986 2,134 1,971
Broking [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 279 259 614 548
Broking [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 778 724 1,520 1,415
Broking [Member] | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 0 [1] 3 [1] 0 8
Consulting [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 748 734 1,515 1,497
Consulting [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 651 643 1,313 1,304
Consulting [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 97 87 201 185
Consulting [Member] | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 0 [1] 4 [1] 1 8
Outsourced administration [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 274 262 570 553
Outsourced administration [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 257 245 523 507
Outsourced administration [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 17 17 47 46
Outsourced administration [Member] | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 0 [1] 0 [1] 0 0
Other [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 120 114 255 250
Other [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 64 59 128 128
Other [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 56 55 127 122
Other [Member] | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 0 [1] 0 [1] 0 0
Service        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 2,199 2,096 4,474 4,271
Service | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 1,251 1,206 2,578 2,487
Service | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 948 883 1,895 1,768
Service | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax $ 0 [1] $ 7 [1] $ 1 $ 16
[1] Reimbursable expenses and other, as well as Corporate revenue, are excluded from segment revenue, but included in total revenue on the condensed consolidated statements of comprehensive income. Amounts included in Corporate revenue may include eliminations, adjustments to reserves and impacts from hedged revenue transactions.