Segments and Disaggregated Revenue Revenue from Contract with Customer Excluding Assessed Tax, Sam's Club (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Revenue from External Customer [Line Items]
Net sales	$ 126,981	$ 123,897	$ 379,318	$ 372,586
Sam's Club
Revenue from External Customer [Line Items]
Net sales	14,625	14,521	43,504	42,933
Sam's Club | Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	8,967	8,570	26,342	25,167
Sam's Club | Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	2,831	3,168	8,646	9,348
Sam's Club | Home and apparel
Revenue from External Customer [Line Items]
Net sales	1,228	1,209	3,851	3,809
Sam's Club | Health and wellness
Revenue from External Customer [Line Items]
Net sales	858	813	2,526	2,403
Sam's Club | Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	$ 741	$ 761	$ 2,139	$ 2,206