Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash paid for amounts included in the measurement of:
Operating cash flows from operating leases	$ 616	$ 698
Operating cash flows from finance leases	45	65
Financing cash flows from finance leases	$ 584	$ 576