Market Risk Benefits - Schedule of market risk benefits (Details) - USD ($) $ in Millions	Mar. 31, 2023	Mar. 31, 2022
Market Risk Benefit [Line Items]
Asset	$ 830	$ 666
Liability	5,144	6,081
Net	4,314	5,415
Individual Retirement
Market Risk Benefit [Line Items]
Asset	685	524
Liability	4,680	5,494
Net	3,995	4,970
Group Retirement
Market Risk Benefit [Line Items]
Asset	145	142
Liability	464	587
Net	$ 319	$ 445

Amount, after effect of reinsurance and cumulative increase (decrease) in instrument-specific credit risk, of contract or contract feature in long-duration contract issued by insurance entity that both protects contract holder from other-than-nominal capital market risk and exposes insurance entity to other-than-nominal capital market risk.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 55
-Paragraph 29G
-URI https://asc.fasb.org/extlink&oid=126561865&loc=SL117819547-158441

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 50
-Paragraph 7B
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=124506351&loc=SL117782768-158439

Reference 3: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 40
-Section 65
-Paragraph 2
-Subparagraph (h)(1)
-URI https://asc.fasb.org/extlink&oid=124501264&loc=SL117420844-207641

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