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Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2022 | Jun. 30, 2021 | Jun. 30, 2022 | Jun. 30, 2021
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | $ 5,379 | $ 5,017 | $ 10,928 | $ 10,100
Risk and Insurance Services Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 3,313 | 3,141 | 6,862 | 6,366
Fiduciary interest income | 13 | 3 | 17 | 8
Risk and Insurance Services Segment | Total International |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 1,245 | 1,246 | 2,512 | 2,447
Risk and Insurance Services Segment | EMEA |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 745 | 796 | 1,587 | 1,633
Risk and Insurance Services Segment | Asia Pacific |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 382 | 347 | 703 | 621
Risk and Insurance Services Segment | Latin America |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 118 | 103 | 222 | 193
Risk and Insurance Services Segment | U.S./Canada |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 1,533 | 1,404 | 2,812 | 2,528
Consulting Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 2,084 | 1,892 | 4,094 | 3,765
Consulting Segment | Wealth |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 597 | 625 | 1,214 | 1,248
Consulting Segment | Health |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 587 | 462 | 1,111 | 949
Consulting Segment | Career |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 205 | 187 | 407 | 365
Marsh & Guy Carpenter | Risk and Insurance Services Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 3,300 | 3,138 | 6,845 | 6,358
Marsh Insurance Group | Risk and Insurance Services Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 2,778 | 2,650 | 5,324 | 4,975
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 522 | 488 | 1,521 | 1,383
Mercer Consulting Group | Consulting Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | 1,389 | 1,274 | 2,732 | 2,562
Oliver Wyman Group Consulting Group | Consulting Segment |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |
Revenue | $ 695 | $ 618 | $ 1,362 | $ 1,203

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