Leases - Components of Lease Expense (Details) - USD ($) $ in Millions	5 Months Ended	12 Months Ended
	Mar. 31, 2017	Mar. 31, 2020	Mar. 31, 2019
Leases [Abstract]
Amortization of leased assets	$ 57	$ 122	$ 117
Interest on lease obligations		17
Total finance lease expense		139
Operating lease expense		54
Variable lease expense		11
Sublease income		(4)
Total lease expense, net		$ 200