Fair Value Measurements Investment in JD (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2018	Jul. 31, 2018	Jul. 31, 2017	Feb. 01, 2018	Jan. 31, 2018
Investment in JD [Line Items]
Unrealized (Gain) Loss on Investments		$ 1,939	$ 0
Investment in JD, cost basis	$ 3,391	3,391
Investment in JD, carrying value					$ 5,037
Investment in JD, fair value	5,174	5,174		$ 7,106
Inputs, Level 1 [Member]
Investment in JD [Line Items]
Investment in JD, cost basis	1,901	1,901
Investment in JD, carrying value					3,547
Investment in JD, fair value	2,584	2,584		3,547
Inputs, Level 2 [Member]
Investment in JD [Line Items]
Investment in JD, cost basis	1,490	1,490
Investment in JD, carrying value					$ 1,490
Investment in JD, fair value	2,590	2,590		$ 3,559
JD [Member]
Investment in JD [Line Items]
Unrealized (Gain) Loss on Investments	$ 100	$ 1,900