XML 95 R77.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Retirement Benefits (Reconciliation of Prior Service Credit) (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Effect of curtailment |  | $ 1 | $ (102)
Pension Plan |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Total recognized as component of net periodic benefit credit | $ (181) | (130) | (62)
Postretirement Benefits |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Total recognized as component of net periodic benefit credit | 1 | 6 | 9
United States | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Pension Plan |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning balance | 0 | 0 |
Amortization of net loss | 0 | 0 |
Ending balance, December 31 | 0 | 0 | 0
United States | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Postretirement Benefits |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning balance | 0 | (3) |
Amortization of net loss | 0 | 3 |
Ending balance, December 31 | 0 | 0 | (3)
Foreign Plan | Pension Plan |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Total recognized as component of net periodic benefit credit | (114) | (74) | (127)
Foreign Plan | Postretirement Benefits |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Total recognized as component of net periodic benefit credit | 1 | 2 | 5
Foreign Plan | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Pension Plan |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning balance | 43 | 43 |
Amortization of net loss | (2) | (2) |
Effect of curtailment | 0 | (1) |
Total recognized as component of net periodic benefit credit | (2) | (3) |
Plan amendments | (44) | 0 |
Exchange rate adjustments | 1 | 3 |
Ending balance, December 31 | (2) | 43 | 43
Foreign Plan | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) | Postretirement Benefits |  |  |
Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning balance | 15 | 0 |
Amortization of net loss | 2 | 2 |
Effect of curtailment | 0 | 0 |
Total recognized as component of net periodic benefit credit | (2) | (2) |
Plan amendments | 0 | 17 |
Exchange rate adjustments | (1) | 0 |
Ending balance, December 31 | $ 12 | $ 15 | $ 0

X
- Definition Accumulated Other Comprehensive Income (Loss) [Roll Forward] + References No definition available. + Details
Name: | mmc_AccumulatedOtherComprehensiveIncomeLossRollForward
Namespace Prefix: | mmc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Other Comprehensive Income (Loss), Defined Benefit Plans Adjustment, Plan Amendment Before Tax + References No definition available. + Details
Name: | mmc_OtherComprehensiveIncomeLossDefinedBenefitPlansAdjustmentPlanAmendmentBeforeTax
Namespace Prefix: | mmc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Other Comprehensive Income (Loss), Pension and Other Postretirement Benefit Plans, Foreign Currency Exchange Adjustments Arising During Period, Before Tax + References No definition available. + Details
Name: | mmc_OtherComprehensiveIncomeLossPensionandOtherPostretirementBenefitPlansForeignCurrencyExchangeAdjustmentsArisingDuringPeriodBeforeTax
Namespace Prefix: | mmc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount before tax of increase (decrease) in accumulated equity from transactions and other events and circumstances from non-owner sources, including portion attributable to noncontrolling interest. Excludes net income (loss), and accumulated changes in equity from transactions resulting from investments by owners (distributions to owners). + References No definition available. + Details
Name: | us-gaap_AccumulatedOtherComprehensiveIncomeLossBeforeTax1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of net periodic benefit cost (credit) for defined benefit plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 6 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e2709-114920 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 55 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=112275985&loc=d3e4179-114921 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 + Details
Name: | us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, before tax, of increase (decrease) to other comprehensive income from settlement and curtailment gain (loss) of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e689-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=108410482&loc=d3e1928-114920 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 11 -URI http://asc.fasb.org/extlink&oid=114867106&loc=d3e637-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount before tax of reclassification adjustments of other comprehensive income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669686-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 17B -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL34724394-108580 + Details
Name: | us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodBeforeTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_PensionPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanTypeAxis=us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanSponsorLocationAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_AccumulatedDefinedBenefitPlansAdjustmentNetPriorServiceCostCreditMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_RetirementPlanSponsorLocationAxis=us-gaap_ForeignPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |