Fair Value Measurements (Notional Amounts And Fair Values Of Interest Rate Swaps) (Details) - Recurring - USD ($) $ in Millions	Apr. 30, 2018	Jan. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount	$ 10,645	$ 10,773
Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	203	322
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	4,000
Fair value hedging | Floating-rate interest rate swaps | Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	(145)	(91)
Net investment hedging | Cross-currency 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 swaps | Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	217	208
Cash flow hedging | Cross-currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount	4,395	4,523
Cash flow hedging | Cross-currency swaps | Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ 131	$ 205