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v3.20.4

Segment Information (Selected Information and Details Of Operating Segment Revenue) (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Dec. 31, 2019 | Sep. 30, 2019 | Jun. 30, 2019 | Mar. 31, 2019 | Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue | $ 4,416 | $ 3,968 | $ 4,189 | $ 4,651 | $ 4,264 | $ 3,968 | $ 4,349 | $ 4,071 | $ 17,224 | $ 16,652 | $ 14,950
Fixed Assets, Net | 856 |  |  |  | 858 |  |  |  | 856 | 858 | 701
Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 10,337 | 9,599 | 8,228
Consulting |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 6,976 | 7,143 | 6,779
United States |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 8,168 | 7,840 | 7,219
Fixed Assets, Net | 492 |  |  |  | 462 |  |  |  | 492 | 462 | 403
United Kingdom |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,818 | 2,679 | 2,243
Fixed Assets, Net | 115 |  |  |  | 149 |  |  |  | 115 | 149 | 91
Continental Europe |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,881 | 2,837 | 2,694
Fixed Assets, Net | 74 |  |  |  | 68 |  |  |  | 74 | 68 | 59
Asia Pacific |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,093 | 2,001 | 1,616
Fixed Assets, Net | 105 |  |  |  | 101 |  |  |  | 105 | 101 | 74
Asia Pacific | Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,059 | 953 | 683
Other |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,353 | 1,385 | 1,235
Fixed Assets, Net | $ 70 |  |  |  | $ 78 |  |  |  | 70 | 78 | 74
Operating Segments |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 17,313 | 16,742 | 15,007
Operating Segments | Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 10,337 | 9,599 | 8,228
Operating Segments | Consulting |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 6,976 | 7,143 | 6,779
Corporate/Eliminations |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | (89) | (90) | (57)
Marsh | Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 8,595 | 8,014 | 6,877
Marsh | Operating Segments | Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 8,628 | 8,085 | 6,923
Guy Carpenter | Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,696 | 1,480 | 1,286
Guy Carpenter | Operating Segments | Risk and Insurance Services |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 1,709 | 1,514 | 1,305
Mercer | Consulting |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 4,928 | 5,021 | 4,732
Mercer | Operating Segments | Consulting |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 4,928 | 5,021 | 4,732
Oliver Wyman Group | Consulting |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | 2,048 | 2,122 | 2,047
Oliver Wyman Group | Operating Segments | Consulting |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Revenue |  |  |  |  |  |  |  |  | $ 2,048 | $ 2,122 | $ 2,047

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