Accounting Policies Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	Jul. 31, 2019	Jan. 31, 2019	Jul. 31, 2018	Jan. 31, 2018
Restricted Cash [Abstract]
Restricted Cash	$ 37	$ 34	$ 22	$ 300
Revenue from Contract with Customer [Abstract]
Receivables from transactions with customers, net	2,483		2,538
Deferred gift card revenue	$ 1,765		$ 1,932