Leases and Other Commitments - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jul. 31, 2020	Jul. 31, 2019	Jul. 31, 2020	Jul. 31, 2019
Other Commitments [Line Items]
Operating lease extension term	5 years		5 years
Operating lease termination option			1 year
Total operating lease costs	$ 258	$ 217	$ 537	$ 423
Cash payments on operating leases	224		450
Right-of use assets obtained in exchange for operating lease liabilities	$ 177		$ 366
Operating lease, weighted average remaining lease term	6 years		6 years
Operating lease, weighted average discount rate	2.60%		2.60%
Finance leases, weighted-average remaining lease term	20 years		20 years
Finance lease, weighted average discount rate	4.40%		4.40%
Sublease income, next five years	$ 179		$ 179
Sublease income, thereafter	44		44
Operating leases, not yet commenced	2,400		2,400
Operating lease commitment balance, including leases not yet commenced	5,900		5,900
Letter of credit
Other Commitments [Line Items]
Value of outstanding letters of credit	$ 100		$ 100
Minimum
Other Commitments [Line Items]
Operating lease term	1 year		1 year
Operating lease term, not yet commenced	3 years		3 years
Maximum
Other Commitments [Line Items]
Operating lease term	22 years		22 years
Operating lease term, not yet commenced	18 years		18 years
Facilities Space
Other Commitments [Line Items]
Operating lease commitment balance, including leases not yet commenced	$ 5,400		$ 5,400