Fair Value Measurements Investment in JD (Details) - USD ($) $ in Millions	Apr. 30, 2018	Feb. 01, 2018	Jan. 31, 2018
Investment in JD [Line Items]
Investment in JD, cost basis	$ 3,391
Investment in JD, carrying value			$ 5,037
Investment in JD, fair value	5,268	$ 7,106
Inputs, Level 1 [Member]
Investment in JD [Line Items]
Investment in JD, cost basis	1,901
Investment in JD, carrying value			3,547
Investment in JD, fair value	2,631	3,547
Inputs, Level 2 [Member]
Investment in JD [Line Items]
Investment in JD, cost basis	1,490
Investment in JD, carrying value			$ 1,490
Investment in JD, fair value	$ 2,637	$ 3,559