Leases - Supplemental cash flow information (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2020	Apr. 01, 2019
Leases [Abstract]
Operating cash flows from operating leases	$ (356)	$ (362)	$ (377)
Operating cash flows from finance leases	0	(4)	(3)
Financing cash flows from finance leases	(31)	(31)	(18)
Operating leases	286	321	2,378
Finance leases	32	75	$ 166
Operating lease, right-of-use asset, transition adjustment	$ 1,548	$ 2,100		$ 2,100