Taxes (Schedule of Income Tax Provision) (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Taxes [Abstract]
U.S. federal	$ 2,998	$ 3,454	$ 5,562
U.S. state and local	405	495	622
International	1,377	1,510	1,400
Total current tax provision	4,780	5,459	7,584
U.S. federal	(22)	1,054	(704)
U.S. state and local	(12)	51	(106)
International	(146)	(360)	(216)
Total deferred tax expense (benefit)	(180)	745	(1,026)
Total provision for income taxes	$ 4,600	$ 6,204	$ 6,558