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Pension Plans and Postretirement Benefits - Obligations and Funded Status (Parenthetical) (Detail) (Domestic Plans [Member], USD $)
In Thousands, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Domestic Plans [Member]
 
Defined Benefit Plan Disclosure [Line Items]  
Lump sum settlement to employees resulted in decrease in plan assets $ 54,551us-gaap_DefinedBenefitPlanSettlementsBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= mdr_DomesticDefinedBenefitPlanMember