Derivative Financial Instruments (Balance Sheet Classification Of Financial Instruments) (Details) - USD ($) $ in Millions	Jul. 31, 2019	Jan. 31, 2019
Fair value hedging [Member] | Other assets
Derivative [Line Items]
Derivative assets	$ 33	$ 0
Fair value hedging [Member] | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	3	78
Fair value hedging [Member] | Long-term debt
Derivative [Line Items]
Nonderivative hedging instruments	0	0
Net investment hedging [Member] | Other assets
Derivative [Line Items]
Derivative assets	473	334
Net investment hedging [Member] | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	0	0
Net investment hedging [Member] | Long-term debt
Derivative [Line Items]
Nonderivative hedging instruments	3,707	3,863
Cash flow hedges [Member] | Other assets
Derivative [Line Items]
Derivative assets	0	78
Cash flow hedges [Member] | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	617	350
Cash flow hedges [Member] | Long-term debt
Derivative [Line Items]
Nonderivative hedging instruments	$ 0	$ 0