Leases (Lease Assets and Liabilities) (Details) - USD ($) $ in Millions	Jul. 31, 2020	Jan. 31, 2020
Operating Leases
ROU assets, non-current	$ 908	$ 886
Lease liabilities, current	112	109
Lease liabilities, non-current	781	746
Total lease liabilities	893	855
Finance Leases
ROU assets, non-current	56	58
Lease liabilities, current	4	4
Lease liabilities, non-current	51	55
Total lease liabilities	$ 55	$ 59