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Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions | 3 Months Ended | 6 Months Ended
--- | --- | ---
Jun. 30, 2019 | Jun. 30, 2019
Risk and Insurance Services Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | $ 2,574 | $ 4,997
Fiduciary interest income | 26 | 49
Risk and Insurance Services Segment | EMEA |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 652 | 1,285
Risk and Insurance Services Segment | Asia Pacific |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 291 | 456
Risk and Insurance Services Segment | Latin America |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 116 | 194
Risk and Insurance Services Segment | Total International |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 1,059 | 1,935
Risk and Insurance Services Segment | U.S./Canada |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 1,097 | 1,958
Consulting Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 1,800 | 3,473
Wealth | Consulting Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 613 | 1,156
Health | Consulting Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 458 | 900
Career | Consulting Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 189 | 359
Marsh Insurance Group | Risk and Insurance Services Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 2,156 | 3,893
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 392 | 1,055
Marsh & Guy Carpenter | Risk and Insurance Services Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 2,548 | 4,948
Mercer Consulting Group | Consulting Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | 1,260 | 2,415
Oliver Wyman Group Consulting Group | Consulting Segment |  |
Disaggregation of Revenue [Line Items] |  |
Revenue | $ 540 | $ 1,058

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- Definition Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130543-203045 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130539-203045 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130545-203045 + Details
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