Segments and Disaggregated Revenue Revenue from Contract with Customer Excluding Assessed Tax, Sam's Club (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2019	Jul. 31, 2018	Jul. 31, 2019	Jul. 31, 2018
Revenue from External Customer [Line Items]
Net sales	$ 129,388	$ 127,059	$ 252,337	$ 248,689
Sam's Club
Revenue from External Customer [Line Items]
Net sales	15,049	14,790	28,879	28,412
Sam's Club | Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	9,000	8,585	17,374	16,597
Sam's Club | Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	3,039	3,261	5,816	6,180
Sam's Club | Home and apparel
Revenue from External Customer [Line Items]
Net sales	1,445	1,398	2,623	2,600
Sam's Club | Health and wellness
Revenue from External Customer [Line Items]
Net sales	842	789	1,668	1,590
Sam's Club | Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	$ 723	$ 757	$ 1,398	$ 1,445