v3.26.3
Revenue from Contracts with Customers - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2026
Sep. 30, 2025
Sep. 30, 2026
Sep. 30, 2025
Disaggregation of Revenue [Line Items]        
Total revenue $ 4,101 $ 3,997 $ 13,381 $ 12,881
U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 2,136 2,084 6,166 6,126
Americas other than U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue 384 381 1,176 1,150
U.K.        
Disaggregation of Revenue [Line Items]        
Total revenue 526 525 1,847 1,756
Ireland        
Disaggregation of Revenue [Line Items]        
Total revenue 46 42 146 133
Europe, Middle East, & Africa other than U.K. and Ireland        
Disaggregation of Revenue [Line Items]        
Total revenue 606 555 2,813 2,451
Asia Pacific        
Disaggregation of Revenue [Line Items]        
Total revenue 403 410 1,233 1,265
Operating Segments | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 2,682 2,525 9,190 8,582
Operating Segments | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 1,421 1,475 4,204 4,311
Operating Segments | U.S. | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 1,353 1,229 4,071 3,774
Operating Segments | U.S. | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 785 858 2,108 2,364
Operating Segments | Americas other than U.S. | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 263 260 823 799
Operating Segments | Americas other than U.S. | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 121 121 353 351
Operating Segments | U.K. | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 302 303 1,206 1,144
Operating Segments | U.K. | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 224 222 641 612
Operating Segments | Ireland | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 21 21 68 67
Operating Segments | Ireland | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 25 21 78 66
Operating Segments | Europe, Middle East, & Africa other than U.K. and Ireland | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 443 400 2,095 1,815
Operating Segments | Europe, Middle East, & Africa other than U.K. and Ireland | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 163 155 718 636
Operating Segments | Asia Pacific | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 300 312 927 983
Operating Segments | Asia Pacific | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 103 98 306 282
Eliminations        
Disaggregation of Revenue [Line Items]        
Total revenue (2) (3) (13) (12)
Eliminations | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 0 0 (5) (5)
Eliminations | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue (2) (3) (8) (7)
Corporate/Eliminations        
Disaggregation of Revenue [Line Items]        
Total revenue (2) (3) (13) (12)
Corporate/Eliminations | U.S.        
Disaggregation of Revenue [Line Items]        
Total revenue (2) (3) (13) (12)
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 2,110 1,988 6,628 6,168
Reinsurance Solutions | Operating Segments | Risk Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 572 537 2,562 2,414
Health Solutions | Operating Segments | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue 992 935 2,929 2,733
Wealth Solutions | Operating Segments | Human Capital        
Disaggregation of Revenue [Line Items]        
Total revenue $ 429 $ 540 $ 1,275 $ 1,578