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v3.20.2

Segment Information (Selected Information And Details For MMC's Operating Segments) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2020 | Sep. 30, 2019 | Sep. 30, 2020 | Sep. 30, 2019
Segment Reporting Information [Line Items] |  |  |  |
Revenue | $ 3,968 | $ 3,968 | $ 12,808 | $ 12,388
Operating Income (Loss) | 540 | 467 | 2,495 | 2,085
Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,291 | 2,206 | 7,805 | 7,203
Interest on fiduciary funds | 8 | 31 | 40 | 80
Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,696 | 1,785 | 5,074 | 5,258
Operating Segments |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 3,987 | 3,991 | 12,879 | 12,461
Operating Income (Loss) | 611 | 535 | 2,698 | 2,342
Operating Segments | Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,291 | 2,206 | 7,805 | 7,203
Operating Income (Loss) | 333 | 218 | 1,883 | 1,468
Interest on fiduciary funds | 8 | 31 | 40 | 80
Equity method income | (6) | 10 | 7 | 16
Operating Segments | Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,696 | 1,785 | 5,074 | 5,258
Operating Income (Loss) | 278 | 317 | 815 | 874
Interest on fiduciary funds | 1 | 1 | 1 | 2
Equity method income |  |  | 4 | 10
Corporate/Eliminations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | (19) | (23) | (71) | (73)
Operating Income (Loss) | (71) | (68) | (203) | (257)
Intersegment Eliminations | Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue |  | 3 | 5 | 7
Intersegment Eliminations | Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | $ 19 | $ 20 | $ 66 | $ 66

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