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v3.20.2

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Segment Reporting Information [Line Items] |  |  |  |
Revenue | $ 4,189 | $ 4,349 | $ 8,840 | $ 8,420
Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,603 | 2,574 | 5,514 | 4,997
Risk and Insurance Services Segment | Marsh Insurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,161 | 2,156 | 4,222 | 3,893
Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 433 | 392 | 1,260 | 1,055
Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,616 | 1,800 | 3,378 | 3,473
Consulting Segment | Mercer Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,149 | 1,260 | 2,400 | 2,415
Consulting Segment | Oliver Wyman Group Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 467 | 540 | 978 | 1,058
Operating Segments |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 4,219 | 4,374 | 8,892 | 8,470
Operating Segments | Risk and Insurance Services Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,603 | 2,574 | 5,514 | 4,997
Operating Segments | Risk and Insurance Services Segment | Marsh Insurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 2,168 | 2,174 | 4,244 | 3,927
Operating Segments | Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 435 | 400 | 1,270 | 1,070
Operating Segments | Consulting Segment |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,616 | 1,800 | 3,378 | 3,473
Operating Segments | Consulting Segment | Mercer Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 1,149 | 1,260 | 2,400 | 2,415
Operating Segments | Consulting Segment | Oliver Wyman Group Consulting Group |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | 467 | 540 | 978 | 1,058
Corporate/Eliminations |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |
Revenue | $ (30) | $ (25) | $ (52) | $ (50)

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