Leases - Components of Lease Cost (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Short-term lease cost	$ 7	$ 15
Operating lease cost	113	228
Amortization of right-of-use assets	3	5
Interest on lease liabilities	1	2
Total finance lease cost	4	7
Variable lease cost	31	62
Sublease income	(6)	(14)
Total lease cost	$ 149	$ 298