Derivative Financial Instruments (Balance Sheet Classification Of Financial Instruments) (Details) - USD ($) $ in Millions	Apr. 30, 2018	Jan. 31, 2018
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	145	91
Net investment hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	217	208
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	3,975	4,041
Cash flow hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	252	300
Cash flow hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	$ 121	$ 95