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Fair Value Measurements (Carrying Value And Fair Value Of Long-Term Debt) (Details) (USD $)
In Millions, unless otherwise specified
Apr. 30, 2015
Jan. 31, 2015
Carrying Value    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term Debt $ 44,908us-gaap_LongTermDebt
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember		 $ 45,680us-gaap_LongTermDebt
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_CarryingReportedAmountFairValueDisclosureMember
Fair Value | Fair Value, Inputs, Level 2 [Member]    
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]    
Long-term debt, including amounts due within one year, Fair Value $ 53,100us-gaap_DebtInstrumentFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember		 $ 56,237us-gaap_DebtInstrumentFairValue
/ us-gaap_FairValueByFairValueHierarchyLevelAxis
= us-gaap_FairValueInputsLevel2Member
/ us-gaap_FairValueByMeasurementBasisAxis
= us-gaap_EstimateOfFairValueFairValueDisclosureMember