Taxes (Schedule of Deferred Tax Balances) (Details) - USD ($) $ in Millions	Jan. 31, 2019	Jan. 31, 2018
Income Tax Disclosure [Abstract]
Loss and tax credit carryforwards	$ 2,964	$ 1,989
Accrued liabilities	2,135	2,482
Share-based compensation	245	217
Other	1,131	1,251
Total deferred tax assets	6,475	5,939
Valuation allowances	(2,448)	(1,843)
Deferred tax assets, net of valuation allowance	4,027	4,096
Property and equipment	4,175	3,954
Deferred Tax Liabilities, Intangible Assets	2,099	401
Inventories	1,354	1,153
Other	899	540
Total deferred tax liabilities	8,527	6,048
Net deferred tax liabilities	$ 4,500	$ 1,952