Taxes (Details) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Taxes [Line Items]
Foreign Earnings Repatriated	$ 5,300
Significant Change in Unrecognized Tax Benefits is Reasonably Possible, Amount of Unrecorded Benefit	$ 3,000
Federal statutory income tax rate, pre-Tax Cuts and Jobs Act		35.00%
U.S. statutory tax rate	21.00%	33.80%	35.00%
Tax Cuts and Jobs Act, Provisional Accounting, Deferred Tax Benefit	$ 75	$ 2,100
Net tax benefit recognized		207
Tax Cuts And Jobs Act Of 2017, Complete Accounting, Provisional Income Tax Benefit	$ 442
Effective Income Tax Rate Reconciliation, Tax Cuts and Jobs Act, Transition Tax on Accumulated Foreign Earnings, Percent	15.50%
Transition tax on accumulated foreign earnings, remaining earnings	8.00%
Tax Cuts and Jobs Act, Incomplete Accounting, Transition Tax for Accumulated Foreign Earnings, Provisional Income Tax Expense	$ 413	1,900
Operating loss and capital loss carryforwards expiring by 2039	8,000
Valuation allowances	(2,448)	(1,843)
Unrecognized tax benefits	1,305	1,010	$ 1,050	$ 607
Unrecognized tax benefits that would impact effective tax rate	1,100	690
Unrecognized tax benefits, income tax penalties accrued		$ 12
Operating and capital loss carryforward [Member]
Taxes [Line Items]
Operating loss and capital loss carryforwards	12,200
Other Expense [Member]
Taxes [Line Items]
Foreign Earnings Repatriated	$ 40