v3.26.3
Revenue (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]        
Revenue $ 6,863 $ 6,351 $ 21,864 $ 20,386
Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 6,885 6,372 21,919 20,444
Corporate/Eliminations        
Disaggregation of Revenue [Line Items]        
Revenue (22) (21) (55) (58)
Risk and Insurance Services | Operating Segments        
Disaggregation of Revenue [Line Items]        
Fiduciary interest income 100 109 273 311
Revenue 4,200 3,907 14,074 13,294
Risk and Insurance Services | Operating Segments | Subtotal        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 4,100 3,798 13,801 12,983
Risk and Insurance Services | Operating Segments | Risk        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 3,726 3,400 11,523 10,702
Revenue 3,796 3,472 11,709 10,907
Risk and Insurance Services | Operating Segments | Reinsurance        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 374 398 2,278 2,281
Revenue 404 435 2,365 2,387
Risk and Insurance Services | Operating Segments | Total International        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 1,525 1,311 4,893 4,376
Risk and Insurance Services | Operating Segments | EMEA        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 994 813 3,265 2,878
Risk and Insurance Services | Operating Segments | Asia Pacific        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 384 361 1,192 1,105
Risk and Insurance Services | Operating Segments | Latin America        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 147 137 436 393
Risk and Insurance Services | Operating Segments | U.S./Canada        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 2,201 2,089 6,630 6,326
Consulting | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 2,685 2,465 7,845 7,150
Consulting | Operating Segments | Investments and Retirement        
Disaggregation of Revenue [Line Items]        
Revenue 762 705 2,254 2,060
Consulting | Operating Segments | Health and Benefits        
Disaggregation of Revenue [Line Items]        
Revenue 578 555 1,850 1,757
Consulting | Operating Segments | Workforce and Rewards        
Disaggregation of Revenue [Line Items]        
Revenue 332 319 827 756
Consulting | Operating Segments | People and Investments        
Disaggregation of Revenue [Line Items]        
Revenue 1,672 1,579 4,931 4,573
Consulting | Operating Segments | Management Consulting        
Disaggregation of Revenue [Line Items]        
Revenue $ 1,013 $ 886 $ 2,914 $ 2,577