Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	6 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Operating Leases, Supplemental Cash Flow Information [Abstract]
Cash paid for amounts included in the measurement of operating lease liabilities – operating cash flows	$ 254	$ 307
ROU assets obtained in exchange for lease, net	69	410
Change in lease classification from operating to finance lease	509	253
Finance Leases, Supplemental Cash Flow Information [Abstract]
Interest paid for finance lease liabilities – Operating cash flows	16	25
Cash paid for amounts included in the measurement of finance lease obligations – financing cash flows	276	285
Total cash paid in the measurement of finance lease obligations	292	310
Capital expenditures through finance lease obligations	$ 114	$ 205