Commitments and Contingencies - Commitments under Operating Lease Agreements (Details) - USD ($) $ in Millions		Sep. 30, 2020	Mar. 31, 2020
Amounts due on operating lease liabilities
Remainder of fiscal year	[1]	$ 10
Year 1		23	$ 21
Year 2		15	23
Year 3		12	15
Year 4		10	12
Year 5			10
Year 4 after		58
Year 5 after			58
Total		128	139
Present value discount		(17)	(19)
Total operating lease liability		$ 111	$ 120

[1] Amounts due on operating lease liabilities as of September 30, 2020 excludes the amounts incurred for the six months ended September 30, 2020.