v3.24.3
Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2024
Sep. 30, 2023
Sep. 30, 2024
Sep. 30, 2023
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax $ 2,238 $ 2,124 $ 6,752 $ 6,445
Reimbursable expenses and other [1] 15 17 55 67
Interest and other income 51 42 143 124
Total revenue 2,289 2,166 6,895 6,569
HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 1,334 1,291 3,944 3,811
Reimbursable expenses and other 17 16 [1] 49 [1] 49 [1]
Interest and other income 11 7 29 22
Total revenue 1,345 1,298 3,973 3,833
R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 909 831 2,810 2,605
Reimbursable expenses and other [1] 3 3 9 9
Interest and other income 34 27 96 63
Total revenue 943 858 2,906 2,668
Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax (5) [1] 2 [1] (2) 29
Reimbursable expenses and other [1] (5) (2) (3) 9
Interest and other income 6 [1] 8 [1] 18 39
Total revenue 1 [1] 10 [1] 16 68
Broking [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 1,006 914 3,140 2,885
Broking [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 262 241 876 789
Broking [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 744 673 2,264 2,088
Broking [Member] | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 0 [1] 0 [1] 0 8
Consulting [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 746 735 2,261 2,232
Consulting [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 653 643 1,966 1,947
Consulting [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 93 88 294 273
Consulting [Member] | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 0 [1] 4 [1] 1 12
Outsourced administration [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 284 293 854 846
Outsourced administration [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 268 272 791 779
Outsourced administration [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 16 21 63 67
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 187 165 442 415
Other [Member] | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 134 119 262 247
Other [Member] | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 53 46 180 168
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 2,223 2,107 6,697 6,378
Service | HWC [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 1,317 1,275 3,895 3,762
Service | R&B [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax 906 828 2,801 2,596
Service | Corporate Segment [Member]        
Disaggregation Of Revenue [Line Items]        
Revenue from Contract with Customer, Excluding Assessed Tax $ 0 [1] $ 4 [1] $ 1 $ 20
[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.