Leases - Narrative (Details) - USD ($) $ in Millions		12 Months Ended
	Apr. 01, 2019	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2018
Lessee, Lease, Description [Line Items]
Operating lease liability	$ 2,200	$ 2,257	$ 2,014
Operating lease right-of-use assets	2,100	2,100	1,886
Cumulative effect adjustment		175	5,309	$ 8,287	$ 10,057
Rent expense				576
Minimum sublease income		202
Future lease payments		217
Total lease receivable		$ 298	$ 272
Remaining lease term		7 years	7 years
Real Property
Lessee, Lease, Description [Line Items]
Renewal option increments for leases (in years)		5 years
Minimum
Lessee, Lease, Description [Line Items]
Noncancelable lease terms		5 years
Minimum | Building
Lessee, Lease, Description [Line Items]
Lease term		1 year
Minimum | Equipment
Lessee, Lease, Description [Line Items]
Lease term		1 year
Maximum
Lessee, Lease, Description [Line Items]
Noncancelable lease terms		15 years
Maximum | Building
Lessee, Lease, Description [Line Items]
Lease term		15 years
Maximum | Equipment
Lessee, Lease, Description [Line Items]
Lease term		5 years
Opening retained earnings adjustments: adoption of new accounting standard
Lessee, Lease, Description [Line Items]
Cumulative effect adjustment			$ (13)	11	154
Impairment charges	89
Retained Earnings
Lessee, Lease, Description [Line Items]
Cumulative effect adjustment		$ 8,202	13,022	12,409	12,986
Retained Earnings | Opening retained earnings adjustments: adoption of new accounting standard
Lessee, Lease, Description [Line Items]
Cumulative effect adjustment	$ 69		$ (13)	$ 11	$ 154