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Revenue - Narrative (Details) $ in Millions | 3 Months Ended
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Mar. 31, 2019 USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Percentage of total revenue | 1.00%
Contract with customer, asset, additions | $ 128
Contract with customer, asset, reclassified to receivable | 42
Contract with customer, liability, revenue recognized | 169
Performance obligation satisfied in previous period | 17
Marsh Insurance Group |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Revenue, remaining performance obligation | $ 30
Mercer Consulting Group |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Consulting revenue, payment terms (in days) | 30 days
Revenue, remaining performance obligation | $ 429
Oliver Wyman Group Consulting Group |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Revenue, remaining performance obligation | $ 3
Risk and Insurance Services Segment |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Insurance brokerage commissions, payment terms (in days) | 30 days
Health Brokerage and Consulting |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Revenue from contract with customer, percent | 65.00%
Minimum | Oliver Wyman Group Consulting Group |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Consulting revenue, payment terms (in days) | 30 days
Minimum | Risk and Insurance Services Segment |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Estimated brokerage revenue, payment terms (in months) | 12 months
Reinsurance brokerage revenue, payment terms (in months) | 12 months
Maximum | Oliver Wyman Group Consulting Group |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Consulting revenue, payment terms (in days) | 60 days
Maximum | Risk and Insurance Services Segment |
Revenue, Initial Application Period Cumulative Effect Transition [Line Items] |
Estimated brokerage revenue, payment terms (in months) | 18 months
Reinsurance brokerage revenue, payment terms (in months) | 18 months

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- Definition Estimated Brokerage Revenue, Payment Terms + References No definition available. + Details
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- Definition Amount of increase (decrease) in revenue recognized for cumulative catch-up adjustment from change in measure of progress which increases (decreases) right to consideration in exchange for good or service transferred to customer when right is conditioned on something other than passage of time. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 606 -SubTopic 10 -Section 50 -Paragraph 10 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109196051&loc=SL49130551-203045 + Details
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