Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Amortization of leased assets	$ 29	$ 65
Interest on lease obligations	5	10
Total finance lease expense	34	75
Operating lease expense	16	30
Variable lease expense	2	4
Sublease income	(1)	(2)
Total lease expense, net	$ 51	$ 107