Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash paid for amounts included in the measurement of:
Operating cash flows used in operating leases	$ 307	$ 340
Operating cash flows used in finance leases	25	34
Financing cash flows used in finance leases	$ 285	$ 279