Leases - Other Information (Details) $ in Millions	12 Months Ended
	Jan. 31, 2020 USD ($)
Leases [Abstract]
Operating cash flows used for operating leases	$ 825
Operating cash flows used for finance leases	30
Financing cash flows used for finance leases	57
Leased assets obtained in exchange for new finance lease liabilities	329
Leased assets obtained in exchange for new operating lease liabilities	$ 551