Fair Value Measurements (Notional Amounts And Fair Values Of Interest Rate Swaps) (Details) - Recurring - USD ($) $ in Millions	Apr. 30, 2019	Jan. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount	$ 10,340	$ 10,423
Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	(58)	(16)
Fair value hedging | Interest Rate Swap [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount	4,000	4,000
Fair value hedging | Interest Rate Swap [Member] | Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	(42)	(78)
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	392	334
Cash flow hedges | Cross-currency swaps
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Notional amount	4,090	4,173
Cash flow hedges | Cross-currency swaps | Inputs, Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value	$ (408)	$ (272)