v3.25.4

Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 26,981	$ 24,458	$ 22,736
Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	27,059	24,528	22,798
Corporate/Eliminations
Disaggregation of Revenue [Line Items]
Revenue	(78)	(70)	(62)
Risk and Insurance Services
Disaggregation of Revenue [Line Items]
Fiduciary interest income	403	497	453
Risk and Insurance Services | Operating Segments
Disaggregation of Revenue [Line Items]
Fiduciary interest income	403	497	453
Revenue	17,265	15,395	14,089
Risk and Insurance Services | Operating Segments | Marsh & Guy Carpenter
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	16,862	14,898	13,636
Risk and Insurance Services | Operating Segments | Marsh Insurance Group
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	14,366	12,536	11,378
Revenue	14,630	12,851	11,657
Risk and Insurance Services | Operating Segments | Guy Carpenter Reinsurance Group
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	2,496	2,362	2,258
Revenue	2,635	2,544	2,432
Risk and Insurance Services | Operating Segments | Total International
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	5,843	5,519	5,116
Risk and Insurance Services | Operating Segments | EMEA
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	3,812	3,530	3,262
Risk and Insurance Services | Operating Segments | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	1,460	1,414	1,295
Risk and Insurance Services | Operating Segments | Latin America
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	571	575	559
Risk and Insurance Services | Operating Segments | U.S./Canada
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	8,523	7,017	6,262
Consulting | Operating Segments
Disaggregation of Revenue [Line Items]
Revenue	9,794	9,133	8,709
Consulting | Operating Segments | U.S. Health And Benefits And U.K Pension Administration Businesses
Disaggregation of Revenue [Line Items]
Pre-tax gain (loss) on sale		35
Consulting | Operating Segments | Wealth
Disaggregation of Revenue [Line Items]
Revenue	2,819	2,584	2,507
Consulting | Operating Segments | Wealth | U.S. Health And Benefits And U.K Pension Administration Businesses
Disaggregation of Revenue [Line Items]
Pre-tax gain (loss) on sale		70
Consulting | Operating Segments | Health
Disaggregation of Revenue [Line Items]
Revenue	2,284	2,100	2,061
Consulting | Operating Segments | Health | U.S. Health And Benefits And U.K Pension Administration Businesses
Disaggregation of Revenue [Line Items]
Pre-tax gain (loss) on sale		(35)
Consulting | Operating Segments | Career
Disaggregation of Revenue [Line Items]
Revenue	1,087	1,059	1,019
Consulting | Operating Segments | Mercer Consulting Group
Disaggregation of Revenue [Line Items]
Revenue	6,190	5,743	5,587
Consulting | Operating Segments | Marsh Management Consulting
Disaggregation of Revenue [Line Items]
Revenue	$ 3,604	3,390	$ 3,122
Pre-tax gain (loss) on sale		$ 20

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