Derivative Financial Instruments (Balance Sheet Classification Of Financial Instruments) (Details) - USD ($) $ in Millions	Jan. 31, 2018	Jan. 31, 2017
Fair value hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	$ 0	$ 8
Fair value hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	91	12
Net investment hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	208	471
Net investment hedging | Long-term debt
Derivative [Line Items]
Nonderivative hedging instruments	4,041	3,209
Cash flow hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	300	0
Cash flow hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	$ 95	$ 618