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Acquisitions, Disposals, and Related Items (Details) - USD ($) $ in Millions					12 Months Ended
	Apr. 04, 2017	Sep. 09, 2016	Jun. 01, 2016	Jul. 01, 2015	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Sep. 19, 2016
Significant Acquisitions and Disposals [Line Items]
Investment and business acquisitions, net of cash acquired					$ 375	$ 2,463	$ 0
Goodwill					18,242	17,037	16,695
Proceeds from the disposal of certain operations					1,046	662	246
Purchase of available for sale securities					0	$ 1,901	$ 0
Yihaodian
Significant Acquisitions and Disposals [Line Items]
Purchase of interests of noncontrolling interest				$ 760
JD.com [Member]
Significant Acquisitions and Disposals [Line Items]
Purchase of available for sale securities					$ 1,900
Noncash or part noncash acquisition, interest acquired					5.00%
Aggregate ownership, percent					10.00%
Suburbia [Member]
Significant Acquisitions and Disposals [Line Items]
Proceeds from the disposal of certain operations	$ 1,000
Gain (loss) on disposition of business, including deferred portion	700
Net gain on disposition of business	$ 400
Gain deferral period					20 years
Yihaodian
Significant Acquisitions and Disposals [Line Items]
Noncash or part noncash divestiture, type of consideration received			Class A ordinary shares
Available for sale securities, percent					5.00%
Noncash or part noncash divestiture, amount of consideration received			$ 1,500
Gain (loss) on disposition of assets			$ 535
Jet.com [Member]
Significant Acquisitions and Disposals [Line Items]
Investment and business acquisitions, net of cash acquired		$ 2,400
Goodwill								$ 1,700
Business combination, recognized identifiable assets acquired and liabilities assumed, intangible assets, other than goodwill								600
Additional compensation over five year period								$ 800