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v3.21.1

Segment Information (Selected Information And Details For MMC's Operating Segments) (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2021 | Mar. 31, 2020
Segment Reporting Information [Line Items] |  |
Revenue | $ 5,083 | $ 4,651
Operating Income (Loss) | 1,358 | 1,070
Risk and Insurance Services Segment |  |
Segment Reporting Information [Line Items] |  |
Revenue | 3,225 | 2,911
Interest on fiduciary funds | 5 | 23
Consulting Segment |  |
Segment Reporting Information [Line Items] |  |
Revenue | 1,873 | 1,762
Operating Segments |  |
Segment Reporting Information [Line Items] |  |
Revenue | 5,098 | 4,673
Operating Income (Loss) | 1,421 | 1,136
Operating Segments | Risk and Insurance Services Segment |  |
Segment Reporting Information [Line Items] |  |
Revenue | 3,225 | 2,911
Operating Income (Loss) | 1,060 | 854
Interest on fiduciary funds | 5 | 23
Operating Segments | Consulting Segment |  |
Segment Reporting Information [Line Items] |  |
Revenue | 1,873 | 1,762
Operating Income (Loss) | 361 | 282
Corporate/Eliminations |  |
Segment Reporting Information [Line Items] |  |
Revenue | (15) | (22)
Operating Income (Loss) | (63) | (66)
Intersegment Eliminations | Consulting Segment |  |
Segment Reporting Information [Line Items] |  |
Revenue | $ 15 | $ 21

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