Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Taxes [Line Items]
Federal statutory income tax rate, pre-Tax Cuts and Jobs Act	35.00%
Federal statutory income tax rate, post-Tax Cuts and Jobs Act	21.00%
U.S. statutory tax rate	33.80%	35.00%	35.00%
Net tax benefit recognized	$ 200
Transition tax on accumulated foreign earnings, for cash and other net current assets	15.50%
Transition tax on accumulated foreign earnings, remaining earnings	8.00%
Provisional transition tax for accumulated foreign earnings	$ 1,900
Provisional deferred tax benefit from change in tax rate	2,100
Amount tax basis exceeds outside book basis of foreign subsidiaries	10,000
Operating loss and capital loss carryforwards expiring by 2038	3,600
Valuation allowances	(1,843)	$ (1,494)
Unrecognized tax benefits	1,010	1,050	$ 607	$ 838
Unrecognized tax benefits that would impact effective tax rate	690	703
Interest and penalty expense (benefit) related to uncertain tax positions	32	35	$ 5
Unrecognized tax benefits, interest on income taxes accrued	96	72
Unrecognized tax benefits, income tax penalties accrued	12	$ 0
Minimum
Taxes [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, amount of unrecorded benefit	50
Maximum
Taxes [Line Items]
Significant change in unrecognized tax benefits is reasonably possible, amount of unrecorded benefit	400
Operating and capital loss carryforward [Member]
Taxes [Line Items]
Operating loss and capital loss carryforwards	$ 6,700