Derivative Financial Instruments (Balance Sheet Classification Of Financial Instruments) (Details) - USD ($) $ in Millions	Apr. 30, 2019	Jan. 31, 2019
Fair value hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	$ 0	$ 0
Fair value hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	42	78
Net investment hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	392	334
Net investment hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	0	0
Net investment hedging | Long-term debt
Derivative [Line Items]
Nonderivative hedging instruments	3,794	3,863
Cash flow hedges | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	41	78
Cash flow hedges | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	$ 449	$ 350