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v3.21.2

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Segment Reporting Information [Line Items] |  |  |  |
Revenue | $ 4,583 | $ 3,968 | $ 14,683 | $ 12,808
Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,670 | 2,291 | 9,036 | 7,805
Risk and Insurance Services Segment | Marsh Insurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,352 | 2,009 | 7,327 | 6,231
Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 314 | 274 | 1,697 | 1,534
Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,925 | 1,696 | 5,690 | 5,074
Consulting Segment | Mercer Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,315 | 1,216 | 3,877 | 3,616
Consulting Segment | Oliver Wyman Group Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 610 | 480 | 1,813 | 1,458
Operating Segments |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 4,595 | 3,987 | 14,726 | 12,879
Operating Segments | Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,670 | 2,291 | 9,036 | 7,805
Operating Segments | Risk and Insurance Services Segment | Marsh Insurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,355 | 2,015 | 7,336 | 6,259
Operating Segments | Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 315 | 276 | 1,700 | 1,546
Operating Segments | Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,925 | 1,696 | 5,690 | 5,074
Operating Segments | Consulting Segment | Mercer Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,315 | 1,216 | 3,877 | 3,616
Operating Segments | Consulting Segment | Oliver Wyman Group Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 610 | 480 | 1,813 | 1,458
Corporate/Eliminations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | $ (12) | $ (19) | $ (43) | $ (71)

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