Acquisitions, Disposals and Related Items (Details) £ in Billions				3 Months Ended	6 Months Ended		12 Months Ended
	Aug. 18, 2018 USD ($)	Apr. 30, 2018 GBP (£)	Apr. 04, 2017 USD ($)	Jul. 31, 2018 USD ($)	Jul. 31, 2018 USD ($)	Jul. 31, 2017 USD ($)	Jan. 31, 2018	Aug. 01, 2018 USD ($)
Business Acquisition [Line Items]
Proceeds from divestiture of businesses					$ 0	$ 1,012,000,000
(Gain) Loss on Disposition of Business					4,755,000,000	0
Payments to Acquire Businesses, Net of Cash Acquired					0	$ 363,000,000
Subsequent Event [Member] | Flipkart [Member]
Business Acquisition [Line Items]
Payments to Acquire Businesses, Net of Cash Acquired	$ 16,000,000,000
Aggregate ownership, percent	77.00%
Subsequent Event [Member] | Flipkart [Member] | Equity Securities [Member]
Business Acquisition [Line Items]
New equity funding	$ 2,000,000,000
Suburbia [Member]
Business Acquisition [Line Items]
Proceeds from divestiture of businesses			$ 1,000,000,000
Gain (loss) on disposition of business, including deferred portion			700,000,000
(Gain) Loss on Disposition of Business			(400,000,000)
Gain (loss) on disposition of business, deferred portion			$ 300,000,000
Gain deferral period							20 years
Walmart Brazil [Member]
Business Acquisition [Line Items]
(Gain) Loss on Disposition of Business				$ 4,800,000,000
Disposal Group, Including Discontinued Operation, Assets				3,300,000,000	3,300,000,000
Disposal Group, Including Discontinued Operation, Liabilities				1,300,000,000	1,300,000,000
Disposal Group, Including Discontinued Operation, Accounts Payable				700,000,000	700,000,000
Disposal Group, Including Discontinued Operation, Other Liabilities, Current				100,000,000	100,000,000
Disposal Group, Including Discontinued Operation, Deferred Tax Liabilities				500,000,000	500,000,000
Translation Adjustment Functional to Reporting Currency, Net of Tax				$ 2,000,000,000	$ 2,000,000,000
Walmart Brazil [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Equity method investment, ownership percentage								20.00%
Business Combination, Indemnification Assets, Amount as of Acquisition Date								$ 800,000,000
Ownership sold, percent								80.00%
Contingent consideration								$ 250,000,000
Asda [Member]
Business Acquisition [Line Items]
Equity method investment, ownership percentage		42.00%
Proceeds from divestiture of businesses | £		£ 3