Leases - Supplemental Cash Flow Information (Details) $ in Millions	6 Months Ended
	Sep. 30, 2019 USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ (189)
Operating cash flows from finance leases	(2)
Financing cash flows from finance leases	(12)
Right-of-use assets obtained in exchange for lease obligations: Operating leases	2,331
Right-of-use assets obtained in exchange for lease obligations: Finance leases	$ 151