Fair Value Measurement (Investment in JD) (Details) - JD.com [Member] - USD ($) $ in Millions	Jul. 31, 2019	Jan. 31, 2019
Investment in JD [Line Items]
Equity investments	$ 4,314	$ 3,583
Inputs, Level 1 [Member]
Investment in JD [Line Items]
Equity investments	2,155	1,791
Inputs, Level 2 [Member]
Investment in JD [Line Items]
Equity investments	$ 2,159	$ 1,792

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=99377092&loc=SL75136599-209740

Name:	us-gaap_EquitySecuritiesFvNi
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant