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Pension Plans and Postretirement Benefits - Asset Allocations by Asset Category (Detail)
Dec. 31, 2014
Dec. 31, 2013
Domestic Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Weighted average asset allocations, by asset category 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember		 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember
TCN Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Weighted average asset allocations, by asset category 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_ThirdCountryNationalEmployeesPensionPlanMember		 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_ThirdCountryNationalEmployeesPensionPlanMember
Fixed Income [Member] | Domestic Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Weighted average asset allocations, by asset category 85.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember		 85.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember
Fixed Income [Member] | TCN Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Weighted average asset allocations, by asset category 28.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_ThirdCountryNationalEmployeesPensionPlanMember		 25.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_FixedIncomeSecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_ThirdCountryNationalEmployeesPensionPlanMember
Equity Securities [Member] | Domestic Plans [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Weighted average asset allocations, by asset category 15.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember		 15.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember
Equity Securities [Member] | TCN Plan [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Weighted average asset allocations, by asset category 72.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_ThirdCountryNationalEmployeesPensionPlanMember		 75.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis
= us-gaap_EquitySecuritiesMember
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_ThirdCountryNationalEmployeesPensionPlanMember