Future Policy Benefit Reserves - Undiscounted Expected Future Benefit and Expense Payments and Undiscounted Expected Future Gross Premiums (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
Insurance [Abstract]
Expected future benefit and expense payments	$ 33,759	$ 33,674
Expected future gross premiums	$ 5,729	$ 5,969

Amount, before effect of reinsurance, of undiscounted balance for expected future policy benefit and expense component of liability for future policy benefit.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 6
-Subparagraph (b)(1)
-URI https://asc.fasb.org/extlink&oid=124506351&loc=d3e14931-158439

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 55
-Paragraph 29E
-URI https://asc.fasb.org/extlink&oid=126561865&loc=SL117819541-158441

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