Segments and Disaggregated Revenue (Revenue, Sam's Club) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Revenue from External Customer [Line Items]
Net sales	$ 136,824	$ 129,388	$ 270,496	$ 252,337
Sam's Club
Revenue from External Customer [Line Items]
Net sales	16,375	15,049	31,538	28,879
Sam's Club | Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	10,715	8,931	21,076	17,251
Sam's Club | Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	2,068	2,863	4,081	5,481
Sam's Club | Home and apparel
Revenue from External Customer [Line Items]
Net sales	1,953	1,763	3,233	3,193
Sam's Club | Health and wellness
Revenue from External Customer [Line Items]
Net sales	931	842	1,832	1,669
Sam's Club | Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	$ 708	$ 650	$ 1,316	$ 1,285