Commitments and Contingencies - Commitments under Operating Lease Agreements (Details) - USD ($) $ in Millions		Sep. 30, 2019	Mar. 31, 2019
Amounts due on operating lease liabilities as of September 30, 2019
2020	[1]	$ 11
2021		20
2022		21
2023		13
2024		11
Thereafter		62
Total		138
Present value discount		(19)
Total operating lease liability		$ 119
Future minimum lease payments as of March 31, 2019
2020	[1]		$ 22
2021			19
2022			20
2023			12
2024			10
Thereafter			61
Total			$ 144

[1] Amounts due on operating lease liabilities as of September 30, 2019 excludes the amounts incurred for the six months ended September 30, 2019.