v3.26.1
Revenue - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax $ 2,363 $ 2,180
Reimbursable expenses and other [1] 22 21
Interest and other income 49 43
Total revenue 2,412 2,223
HWC [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 1,275 1,173
Reimbursable expenses and other [1] 19 17
Interest and other income 9 9
Total revenue 1,284 1,182
R&B [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 1,086 1,006
Reimbursable expenses and other [1] 3 3
Interest and other income 33 24
Total revenue 1,119 1,030
Corporate [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax [1] 2 1
Reimbursable expenses and other [1] 0 1
Interest and other income [1] 7 10
Total revenue [1] 9 11
Broking [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 1,033 936
Broking [Member] | HWC [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 184 146
Broking [Member] | R&B [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 849 790
Broking [Member] | Corporate [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax [1] 0 0
Consulting [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 861 798
Consulting [Member] | HWC [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 731 679
Consulting [Member] | R&B [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 128 119
Consulting [Member] | Corporate [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax [1] 2 0
Outsourced administration [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 298 289
Outsourced administration [Member] | HWC [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 278 268
Outsourced administration [Member] | R&B [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 20 21
Outsourced administration [Member] | Corporate [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax [1] 0 0
Other [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 149 136
Other [Member] | HWC [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 63 63
Other [Member] | R&B [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 86 73
Other [Member] | Corporate [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax [1] 0 0
Service [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 2,341 2,159
Service [Member] | HWC [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 1,256 1,156
Service [Member] | R&B [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax 1,083 1,003
Service [Member] | Corporate [Member]    
Disaggregation Of Revenue [Line Items]    
Revenue from Contract with Customer, Excluding Assessed Tax [1] $ 2 $ 0
[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.