v3.26.1
Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Revenue [Line Items]        
Total revenue $ 4,246 $ 4,155 $ 9,280 $ 8,884
U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 2,020 2,040 4,030 4,042
Americas other than U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 408 395 792 769
U.K.        
Disaggregation of Revenue [Line Items]        
Total revenue 632 610 1,321 1,231
Ireland        
Disaggregation of Revenue [Line Items]        
Total revenue 47 46 100 91
Europe, Middle East, & Africa other than U.K. and Ireland        
Disaggregation of Revenue [Line Items]        
Total revenue 718 634 2,207 1,896
Asia Pacific        
Disaggregation of Revenue [Line Items]        
Total revenue 421 430 830 855
Operating Segments | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 3,006 2,866 6,508 6,057
Operating Segments | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 1,244 1,291 2,783 2,836
Operating Segments | U.S. | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 1,392 1,324 2,718 2,545
Operating Segments | U.S. | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 632 718 1,323 1,506
Operating Segments | Americas other than U.S. | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 299 285 560 539
Operating Segments | Americas other than U.S. | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 109 110 232 230
Operating Segments | U.K. | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 422 411 904 841
Operating Segments | U.K. | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 210 199 417 390
Operating Segments | Ireland | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 22 24 47 46
Operating Segments | Ireland | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 25 22 53 45
Operating Segments | Europe, Middle East, & Africa other than U.K. and Ireland | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 533 469 1,652 1,415
Operating Segments | Europe, Middle East, & Africa other than U.K. and Ireland | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 185 165 555 481
Operating Segments | Asia Pacific | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 338 353 627 671
Operating Segments | Asia Pacific | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 83 77 203 184
Eliminations        
Disaggregation of Revenue [Line Items]        
Total revenue (4) (2) (11) (9)
Eliminations | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 1 1 5 5
Eliminations | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 3 2 6 4
Corporate/Eliminations        
Disaggregation of Revenue [Line Items]        
Total revenue (4) (2) (11) (9)
Corporate/Eliminations | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue (4) (2) (11) (9)
Corporate/Eliminations | Americas other than U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 0 0 0 0
Corporate/Eliminations | U.K.        
Disaggregation of Revenue [Line Items]        
Total revenue 0 0 0 0
Corporate/Eliminations | Ireland        
Disaggregation of Revenue [Line Items]        
Total revenue 0 0 0 0
Corporate/Eliminations | Europe, Middle East, & Africa other than U.K. and Ireland        
Disaggregation of Revenue [Line Items]        
Total revenue 0 0 0 0
Corporate/Eliminations | Asia Pacific        
Disaggregation of Revenue [Line Items]        
Total revenue 0 0 0 0
Commercial Risk Solutions | Operating Segments | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 2,295 2,178 4,518 4,180
Reinsurance Solutions | Operating Segments | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 711 688 1,990 1,877
Health Solutions | Operating Segments | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 818 772 1,937 1,798
Wealth Solutions | Operating Segments | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue $ 426 $ 519 $ 846 $ 1,038