Segments and Disaggregated Revenue (Revenue, Sam's Club) (Details) - USD ($) $ in Millions	3 Months Ended
Apr. 30, 2020	Apr. 30, 2019
Revenue from External Customer [Line Items]
Net sales	$ 133,672	$ 122,949
Sam's Club
Revenue from External Customer [Line Items]
Net sales	15,163	13,830
Sam's Club \| Grocery and consumables
Revenue from External Customer [Line Items]
Net sales	10,427	8,373
Sam's Club \| Fuel, tobacco and other categories
Revenue from External Customer [Line Items]
Net sales	2,100	2,777
Sam's Club \| Home and apparel
Revenue from External Customer [Line Items]
Net sales	1,074	1,178
Sam's Club \| Health and wellness
Revenue from External Customer [Line Items]
Net sales	901	827
Sam's Club \| Technology, office and entertainment
Revenue from External Customer [Line Items]
Net sales	$ 661	$ 675

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration