Income Taxes - Deferred Tax Liabilities and Assets (Parenthetical) (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Unrealized gains or losses included in accumulated other comprehensive income or loss, deferred tax liabilities	$ 2	$ 4

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

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32632-109319

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32621-109319

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