v3.25.1
Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2025
Mar. 31, 2024
Disaggregation of Revenue [Line Items]    
Total revenue $ 4,729 $ 4,070
U.S.    
Disaggregation of Revenue [Line Items]    
Total revenue 2,002 1,512
Americas other than U.S.    
Disaggregation of Revenue [Line Items]    
Total revenue 374 323
U.K.    
Disaggregation of Revenue [Line Items]    
Total revenue 621 583
Ireland    
Disaggregation of Revenue [Line Items]    
Total revenue 45 33
Europe, Middle East, & Africa other than U.K. and Ireland    
Disaggregation of Revenue [Line Items]    
Total revenue 1,262 1,209
Asia Pacific    
Disaggregation of Revenue [Line Items]    
Total revenue 425 410
Operating Segments | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 3,191 2,975
Operating Segments | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 1,545 1,103
Operating Segments | U.S. | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 1,221 1,078
Operating Segments | U.S. | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 788 442
Operating Segments | Americas other than U.S. | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 254 227
Operating Segments | Americas other than U.S. | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 120 96
Operating Segments | U.K. | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 430 411
Operating Segments | U.K. | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 191 172
Operating Segments | Ireland | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 22 16
Operating Segments | Ireland | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 23 17
Operating Segments | Europe, Middle East, & Africa other than U.K. and Ireland | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 946 928
Operating Segments | Europe, Middle East, & Africa other than U.K. and Ireland | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 316 281
Operating Segments | Asia Pacific | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 318 315
Operating Segments | Asia Pacific | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 107 95
Eliminations    
Disaggregation of Revenue [Line Items]    
Total revenue (7) (8)
Eliminations | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 5 6
Eliminations | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 2 2
Corporate/Eliminations    
Disaggregation of Revenue [Line Items]    
Total revenue (7) (8)
Corporate/Eliminations | U.S.    
Disaggregation of Revenue [Line Items]    
Total revenue (7) (8)
Corporate/Eliminations | Americas other than U.S.    
Disaggregation of Revenue [Line Items]    
Total revenue 0 0
Corporate/Eliminations | U.K.    
Disaggregation of Revenue [Line Items]    
Total revenue 0 0
Corporate/Eliminations | Ireland    
Disaggregation of Revenue [Line Items]    
Total revenue 0 0
Corporate/Eliminations | Europe, Middle East, & Africa other than U.K. and Ireland    
Disaggregation of Revenue [Line Items]    
Total revenue 0 0
Corporate/Eliminations | Asia Pacific    
Disaggregation of Revenue [Line Items]    
Total revenue 0 0
Commercial Risk Solutions | Operating Segments | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 2,002 1,808
Reinsurance Solutions | Operating Segments | Risk Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 1,189 1,167
Health Solutions | Operating Segments | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue 1,026 733
Wealth Solutions | Operating Segments | Human Capital    
Disaggregation of Revenue [Line Items]    
Total revenue $ 519 $ 370