XML 87 R58.htm IDEA: XBRL DOCUMENT v2.4.1.9
Retirement Benefits (Narrative) (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Jan. 31, 2014
Defined Benefit Plan Disclosure [Line Items]      
Contributions to U.S. non qualified and non-U.S. Pension Plan $ 42us-gaap_DefinedBenefitPlanContributionsByEmployer    
Postretirement Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit credit 125us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
(4)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Gain (loss) due to curtailments 0us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
0us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
 
Non-U.S. Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit credit 14us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
66us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
 
Effect of plan amendment on accumulated benefit obligation     147us-gaap_DefinedBenefitPlanEffectOfPlanAmendmentOnAccumulatedBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
Effect of plan amendment on funded status     137mmc_DefinedBenefitPlanEffectofPlanAmendmentonFundedStatus
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
Gain (loss) due to curtailments 0us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
65us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
 
Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit credit (31)us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
43us-gaap_DefinedBenefitPlanNetPeriodicBenefitCost
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Gain (loss) due to curtailments 0us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
65us-gaap_DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
 
Expected contribution during remainder of 2013 $ 152us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInCurrentFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember
   
Equity Funds [Member] | United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Target asset allocation U.S. Plan, equities, prior period 62.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquityFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_UnitedStatesPensionandPostretirementBenefitPlanofUSEntityDefinedBenefitMember
   
Actual asset allocation percentage of equity 61.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquityFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_UnitedStatesPensionandPostretirementBenefitPlanofUSEntityDefinedBenefitMember
   
Fixed Income Funds [Member] | United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Target asset allocation U.S. Plan, equities, prior period 38.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_UnitedStatesPensionandPostretirementBenefitPlanofUSEntityDefinedBenefitMember
   
Actual asset allocation percentage of equity 39.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_UnitedStatesPensionandPostretirementBenefitPlanofUSEntityDefinedBenefitMember
   
United Kingdom [Member] | Equity Funds [Member] | Non-U.S. Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Target asset allocation U.S. Plan, equities, prior period 48.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquityFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_ForeignPensionandPostretirementBenefitPlanDefinedBenefitMember
/ us-gaap_StatementGeographicalAxis
= country_GB
   
Actual asset allocation percentage of equity 47.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquityFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_ForeignPensionandPostretirementBenefitPlanDefinedBenefitMember
/ us-gaap_StatementGeographicalAxis
= country_GB
   
United Kingdom [Member] | Fixed Income Funds [Member] | Non-U.S. Plans [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Target asset allocation U.S. Plan, equities, prior period 52.00%us-gaap_DefinedBenefitPlanTargetPlanAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_ForeignPensionandPostretirementBenefitPlanDefinedBenefitMember
/ us-gaap_StatementGeographicalAxis
= country_GB
   
Actual asset allocation percentage of equity 53.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeFundsMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mmc_ForeignPensionandPostretirementBenefitPlanDefinedBenefitMember
/ us-gaap_StatementGeographicalAxis
= country_GB
   
United Kingdom [Member] | Geographic Concentration Risk [Member] | Non-U.S. Plans [Member] | Non-U.S. Pension Benefits [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Concentration risk percentage 83.00%us-gaap_ConcentrationRiskPercentage1
/ us-gaap_ConcentrationRiskByBenchmarkAxis
= mmc_ForeignPensionandPostretirementBenefitPlanDefinedBenefitMember
/ us-gaap_ConcentrationRiskByTypeAxis
= us-gaap_GeographicConcentrationRiskMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPensionPlansDefinedBenefitMember
/ us-gaap_StatementGeographicalAxis
= country_GB