Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Lessee, Lease, Description [Line Items]
Rent expense		$ 576	$ 568
Minimum sublease income	$ 178
Future lease payments	149
Future minimum lease payments for sale leaseback transaction		49
Minimum sublease income, due under future noncancelable subleases		$ 133
Total lease receivable	$ 272
Remaining lease term	7 years
Minimum
Lessee, Lease, Description [Line Items]
Noncancelable lease terms	2 years
Maximum
Lessee, Lease, Description [Line Items]
Noncancelable lease terms	15 years
Building | Minimum
Lessee, Lease, Description [Line Items]
Lease term	1 year
Building | Maximum
Lessee, Lease, Description [Line Items]
Lease term	15 years
Equipment | Minimum
Lessee, Lease, Description [Line Items]
Lease term	1 year
Equipment | Maximum
Lessee, Lease, Description [Line Items]
Lease term	5 years
Real Property
Lessee, Lease, Description [Line Items]
Renewal option increments for leases (in years)	5 years