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Fair Value Measurements (Notional Amounts And Fair Values Of Interest Rate Swaps) (Details) - Recurring - USD ($) $ in Millions | Jan. 31, 2018 | Jan. 31, 2017
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Notional amount | $ 10,773 | $ 11,207
Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 322 | (151)
Fair value hedging | Floating-rate interest rate swaps |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Notional amount | 4,000 | 5,000
Fair value hedging | Floating-rate interest rate swaps | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | (91) | (4)
Net investment hedging | Cross-currency interest rate swaps |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Notional amount | 2,250 | 2,250
Net investment hedging | Cross-currency interest rate swaps | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | 208 | 471
Cash flow hedging | Cross-currency interest rate swaps |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Notional amount | 4,523 | 3,957
Cash flow hedging | Cross-currency interest rate swaps | Fair value, inputs, level 2 |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Fair value | $ 205 | $ (618)

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