Segments and Disaggregated Revenue Revenue from Contract with Customer Excluding Assessed Tax, Sam's Club (Details) - USD ($) $ in Millions	3 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Revenue from External Customer [Line Items]
Net sales	$ 122,949	$ 121,630
Sam's Club
Revenue from External Customer [Line Items]
Net sales	13,830	13,622
Sam's Club | Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	8,373	8,012
Sam's Club | Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	2,777	2,919
Sam's Club | Home and apparel
Revenue from External Customer [Line Items]
Net sales	1,178	1,202
Sam's Club | Health and wellness
Revenue from External Customer [Line Items]
Net sales	827	801
Sam's Club | Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	675	688
eCommerceMember | Sam's Club
Revenue from External Customer [Line Items]
Net sales	$ 700	$ 600