v3.25.4

Segment Information (Operating Segment Revenue) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	$ 26,981	$ 24,458	$ 22,736
Operating Segments
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	27,059	24,528	22,798
Operating Segments | Risk and Insurance Services
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	17,265	15,395	14,089
Operating Segments | Risk and Insurance Services | Marsh Insurance Group
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	14,630	12,851	11,657
Operating Segments | Risk and Insurance Services | Guy Carpenter Reinsurance Group
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	2,635	2,544	2,432
Operating Segments | Consulting
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	9,794	9,133	8,709
Operating Segments | Consulting | Mercer Consulting Group
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	6,190	5,743	5,587
Operating Segments | Consulting | Marsh Management Consulting
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	3,604	3,390	3,122
Corporate/Eliminations
Segment Reporting, Asset Reconciling Item [Line Items]
Revenue	$ (78)	$ (70)	$ (62)

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