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v3.24.3

Segment Information (Selected Information and Details for MMC's Operating Segments) (Details) - USD ($) $ in Millions |  | 3 Months Ended | 9 Months Ended
--- | --- | --- | ---
Jan. 01, 2024 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2024 | Sep. 30, 2023
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  | $ 5,697 | $ 5,382 | $ 18,391 | $ 17,182
Operating Income/(Loss) |  | 1,108 | 996 | 4,675 | 4,179
Discontinued Operations, Disposed of by Sale | 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 |  |  |  |
Total Segments |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  | 5,715 | 5,396 | 18,440 | 17,227
Operating Income/(Loss) |  | 1,195 | 1,064 | 4,899 | 4,415
Total Segments | Discontinued Operations, Disposed of by Sale | 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 |
Total Segments | Risk and Insurance Services |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  | 3,453 | 3,190 | 11,748 | 10,818
Operating Income/(Loss) |  | 733 | 640 | 3,595 | 3,192
Interest on fiduciary funds |  | 138 | 131 | 385 | 330
Equity method investment income (loss) |  | 7 | 3 | 17 | 14
Total Segments | Consulting |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  | 2,262 | 2,206 | 6,692 | 6,409
Operating Income/(Loss) |  | 462 | 424 | 1,304 | 1,223
Corporate/Eliminations |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  | (18) | (14) | (49) | (45)
Operating Income/(Loss) |  | (87) | (68) | (224) | (236)
Intersegment Eliminations | Risk and Insurance Services |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  |  |  | 5 | 5
Intersegment Eliminations | Consulting |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |
Revenue |  | $ 18 | $ 14 | $ 44 | $ 40

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