Income Taxes - Deferred Tax Liabilities and Assets (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Unrealized gains or losses included in accumulated other comprehensive income or loss, deferred tax liabilities	$ 4	$ 1

Amount of deferred tax liability attributable to taxable temporary differences from unrealized gains in other comprehensive income.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant