Leases and Other Commitments - Components of Lease Expense and Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jul. 31, 2019	Jul. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Operating lease cost	$ 217	$ 423
Finance lease cost:
Amortization of right-of-use assets	17	33
Interest on lease liabilities	5	11
Interest on lease liabilities	22	44
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash outflows for operating leases	209	391
Operating cash outflows for finance leases	4	8
Financing cash outflows for finance leases	134	136
Right-of-use assets obtained in exchange for lease obligations:
Operating leases	$ 171	$ 330