Segments and Disaggregated Revenue (Revenue, Sam's Club) (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 30, 2021	Apr. 30, 2020
Revenue from External Customer [Line Items]
Net sales	$ 137,159	$ 133,672
Sam's Club
Revenue from External Customer [Line Items]
Net sales	16,692	15,163
Sam's Club | eCommerceMember
Revenue from External Customer [Line Items]
Net sales	1,500	1,000
Sam's Club | Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	10,669	10,361
Sam's Club | Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	2,299	2,013
Sam's Club | Home and apparel
Revenue from External Customer [Line Items]
Net sales	2,082	1,280
Sam's Club | Health and wellness
Revenue from External Customer [Line Items]
Net sales	941	901
Sam's Club | Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	$ 701	$ 608