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Employee Benefit Plans - Aggregate Fair Value of CMRT Assets (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]    
CMRT asset value $ 715.5nl_CombinedMasterRetirementTrustAssetValue $ 722.8nl_CombinedMasterRetirementTrustAssetValue
Fair value input 100.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs 100.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
Domestic equities, principally publicly traded 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations 100.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
Domestic Equities Principally Publicly Traded    
Defined Benefit Plan Disclosure [Line Items]    
Domestic equities, principally publicly traded 48.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= nl_DomesticEquitiesPrincipallyPubliclyTradedMember		 53.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= nl_DomesticEquitiesPrincipallyPubliclyTradedMember
IEPT    
Defined Benefit Plan Disclosure [Line Items]    
Domestic equities, principally publicly traded 11.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= nl_InternationalEquitiesPubliclyTradedMember		  
FIPT    
Defined Benefit Plan Disclosure [Line Items]    
Domestic equities, principally publicly traded 32.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_FixedIncomeSecuritiesMember		 35.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_FixedIncomeSecuritiesMember
PMLP    
Defined Benefit Plan Disclosure [Line Items]    
Domestic equities, principally publicly traded 7.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= nl_PrivatelyManagedLimitedPartnershipsMember		 11.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= nl_PrivatelyManagedLimitedPartnershipsMember
OI    
Defined Benefit Plan Disclosure [Line Items]    
Domestic equities, principally publicly traded 2.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_CashAndCashEquivalentsMember		 1.00%us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_CashAndCashEquivalentsMember
Level 1    
Defined Benefit Plan Disclosure [Line Items]    
Fair value input 67.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member		 79.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel1Member
Level 2    
Defined Benefit Plan Disclosure [Line Items]    
Fair value input 13.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member		 4.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
Level 3    
Defined Benefit Plan Disclosure [Line Items]    
Fair value input 20.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member		 17.00%nl_PercentageOfCombinedMasterRetirementTrustFairValueInputs
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel3Member