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Effect of One Percentage-Point Change in Assumed Health Care Cost Trend Rates (Detail) (Supplemental Employee Retirement Plan [Member], USD $)
In Millions, unless otherwise specified
12 Months Ended
Jan. 31, 2015
Supplemental Employee Retirement Plan [Member]
 
Assumed Health Care Cost Trend Rates, Effect of One Percentage Point Change [Line Items]  
Effect on total service and interest cost components, 1% increase $ 0us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Effect on accumulated postretirement benefit obligation, 1% increase 4us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnAccumulatedPostretirementBenefitObligation
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Effect on total service and interest cost components, 1% (decrease) 0us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Effect on accumulated postretirement benefit obligation, 1% (decrease) $ (3)us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnAccumulatedPostretirementBenefitObligation1
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember