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Revenue - Disaggregation of Revenue (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2018 USD ($)
Risk and Insurance Services Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | $ 2,344
Fiduciary interest income | 13
Risk and Insurance Services Segment | EMEA |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 643
Risk and Insurance Services Segment | Asia Pacific |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 164
Risk and Insurance Services Segment | Latin America |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 84
Risk and Insurance Services Segment | Total International |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 891
Risk and Insurance Services Segment | U.S./Canada |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 803
Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 1,668
Defined Benefit Consulting & Administration | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 339
Investment Management & Related Services | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 226
Total Wealth | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 565
Health | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 442
Career | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 164
Marsh Insurance Group | Risk and Insurance Services Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 1,694
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 637
Marsh & Guy Carpenter | Risk and Insurance Services Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 2,331
Mercer Consulting Group | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | 1,171
Oliver Wyman Group Consulting Group | Consulting Segment |
Disaggregation of Revenue [Line Items] |
Revenue from Contract with Customer, Excluding Assessed Tax | $ 497

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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://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 32 -Paragraph 2A -URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 4 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045 + Details
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