v3.25.2
Revenue (Disaggregation of Revenue) (Details) - USD ($)
$ in Millions
3 Months Ended 6 Months Ended
Jun. 30, 2025
Jun. 30, 2024
Jun. 30, 2025
Jun. 30, 2024
Disaggregation of Revenue [Line Items]        
Revenue $ 6,974 $ 6,221 $ 14,035 $ 12,694
Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 6,996 6,238 14,072 12,725
Risk and Insurance Services | Operating Segments        
Disaggregation of Revenue [Line Items]        
Fiduciary interest income 99 125 202 247
Revenue 4,625 4,022 9,387 8,295
Risk and Insurance Services | Subtotal | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 4,526 3,897 9,185 8,048
Risk and Insurance Services | Marsh | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 3,849 3,265 7,302 6,268
Revenue 3,915 3,342 7,435 6,423
Risk and Insurance Services | Guy Carpenter | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 677 632 1,883 1,780
Revenue 710 680 1,952 1,872
Risk and Insurance Services | Total International | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 1,547 1,440 3,065 2,926
Risk and Insurance Services | EMEA | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 1,006 912 2,065 1,937
Risk and Insurance Services | Asia Pacific | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 409 391 744 727
Risk and Insurance Services | Latin America | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 132 137 256 262
Risk and Insurance Services | U.S./Canada | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue, excluding fiduciary interest income 2,302 1,825 4,237 3,342
Consulting | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 2,371 2,216 4,685 4,430
Consulting | Mercer | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 1,498 1,379 2,994 2,804
Consulting | Mercer | Wealth | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 685 612 1,355 1,284
Consulting | Mercer | Health | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 594 547 1,202 1,085
Consulting | Mercer | Career | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue 219 220 437 435
Consulting | Oliver Wyman Group | Operating Segments        
Disaggregation of Revenue [Line Items]        
Revenue $ 873 $ 837 $ 1,691 $ 1,626