Segments and Disaggregated Revenue (Revenue, Sam's Club) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2020	Oct. 31, 2019	Oct. 31, 2020	Oct. 31, 2019
Revenue from External Customer [Line Items]
Net sales	$ 133,752	$ 126,981	$ 404,248	$ 379,318
Sam's Club
Revenue from External Customer [Line Items]
Net sales	15,845	14,625	47,383	43,504
Sam's Club | Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	10,450	8,900	31,526	26,151
Sam's Club | Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	1,942	2,646	6,023	8,127
Sam's Club | Home and apparel
Revenue from External Customer [Line Items]
Net sales	1,693	1,532	4,926	4,725
Sam's Club | Health and wellness
Revenue from External Customer [Line Items]
Net sales	1,017	858	2,849	2,527
Sam's Club | Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	$ 743	$ 689	$ 2,059	$ 1,974