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v3.25.1

Segment Information (Selected Information and Details for MMC's Operating Segments) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2025 | Mar. 31, 2024 | Dec. 31, 2024
Segment Reporting Information [Line Items] |  |  |
Revenue | $ 7,061 | $ 6,473 |
Compensation and benefits | 3,850 | 3,470 |
Depreciation and amortization expense | 88 | 99 |
Amortization of intangible assets | 139 | 90 |
Other operating expenses | 979 | 889 |
Operating income | 2,005 | 1,925 |
Operating Segments |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 7,076 | 6,487 |
Compensation and benefits | 3,814 | 3,432 |
Depreciation and amortization expense | 74 | 83 |
Amortization of intangible assets | 139 | 90 |
Other operating expenses | 980 | 885 |
Operating income | 2,069 | 1,997 |
Operating Segments | Risk and Insurance Services |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 4,762 | 4,273 |
Compensation and benefits | 2,451 | 2,118 |
Depreciation and amortization expense | 50 | 46 |
Amortization of intangible assets | 120 | 79 |
Other operating expenses | 528 | 465 |
Operating income | 1,613 | 1,565 |
Interest on fiduciary funds | 103 | 122 |
Operating Segments | Risk and Insurance Services | Disposal Group, Disposed of by Sale, Not Discontinued Operations |  |  |
Segment Reporting Information [Line Items] |  |  |
Net gain includes in revenue consolidated statements of income | (28) |  |
Operating Segments | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | 2,314 | 2,214 |
Compensation and benefits | 1,363 | 1,314 |
Depreciation and amortization expense | 24 | 37 |
Amortization of intangible assets | 19 | 11 |
Other operating expenses | 452 | 420 |
Operating income | 456 | 432 |
Operating Segments | Consulting | U.S. Health And Benefits And U.K Pension Administration Businesses |  |  |
Segment Reporting Information [Line Items] |  |  |
Net gain includes in revenue consolidated statements of income |  |  | $ (21)
Corporate/Eliminations |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | (15) | (14) |
Compensation and benefits | 36 | 38 |
Depreciation and amortization expense | 14 | 16 |
Amortization of intangible assets | 0 | 0 |
Other operating expenses | (1) | 4 |
Operating income | (64) | (72) |
Intersegment Eliminations | Consulting |  |  |
Segment Reporting Information [Line Items] |  |  |
Revenue | $ 15 | $ 13 |

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