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Nonpension Postretirement Benefits (Assumptions Used) (Details) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Nonpension Postretirement Benefit Plans      
Defined Benefit Plan Disclosure [Line Items]      
Effect of 1.0% change in discount rate on nonpension postretirement benefit expense 0.4lby_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseInDiscountRateOnPostretirementBenefitExpense
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_OtherPostretirementBenefitPlansDefinedBenefitMember
   
U.S. Plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate used to determine accumulated postretirement benefit obligation 4.10%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember
4.74%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember
 
Discount rate used to determine net postretirement benefit cost 4.74%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember
3.85%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember
4.91%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_UnitedStatesPostretirementBenefitPlansOfUSEntityDefinedBenefitMember
Non-U.S. Plans      
Defined Benefit Plan Disclosure [Line Items]      
Discount rate used to determine accumulated postretirement benefit obligation 3.61%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPostretirementBenefitPlansDefinedBenefitMember
4.36%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingBenefitObligationDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPostretirementBenefitPlansDefinedBenefitMember
 
Discount rate used to determine net postretirement benefit cost 4.36%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPostretirementBenefitPlansDefinedBenefitMember
3.71%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPostretirementBenefitPlansDefinedBenefitMember
3.97%us-gaap_DefinedBenefitPlanAssumptionsUsedCalculatingNetPeriodicBenefitCostDiscountRate
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_ForeignPostretirementBenefitPlansDefinedBenefitMember