Derivative Financial Instruments (Balance Sheet Classification Of Financial Instruments) (Details) - USD ($) $ in Millions	Apr. 30, 2017	Jan. 31, 2017
Fair value hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	$ 21	$ 8
Fair value hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	5	12
Net investment hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	395	471
Net investment hedging | Long-term debt
Derivative [Line Items]
Nonderivative hedging instruments	3,328	3,209
Cash flow hedging | Other assets and deferred charges
Derivative [Line Items]
Derivative assets	83	0
Cash flow hedging | Deferred income taxes and other
Derivative [Line Items]
Derivative liabilities	$ 607	$ 618