Fair Value of Financial Instruments - Fair Value Measured on a Recurring Basis Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	$ (129)	$ 3,858	$ 3,858
Items Included in Net Income	(2,990)	(1,240)
Gains (Losses) in OCI and Other	(7)	24
Issuances, Sales, Maturities, Settlements, Calls, Net	360	523
Transfers Into or Out of Level 3, Net	(73)	(166)
Ending Fair Value	$ (2,839)	$ 2,999	$ (129)	$ 3,858
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net income (loss)		Net income (loss)	Net income (loss)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Derivative investments	Derivative investments
Corporate bonds \| Fixed maturity AFS securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	$ 6,469	$ 5,186	$ 5,186
Items Included in Net Income	1	0
Gains (Losses) in OCI and Other	(8)	12
Issuances, Sales, Maturities, Settlements, Calls, Net	310	1,006
Transfers Into or Out of Level 3, Net	(25)	15
Ending Fair Value	6,747	6,219	6,469	$ 5,186
State and municipal bonds \| Fixed maturity AFS securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	5	35	35
Items Included in Net Income	0	0
Gains (Losses) in OCI and Other	0	1
Issuances, Sales, Maturities, Settlements, Calls, Net	0	0
Transfers Into or Out of Level 3, Net	(5)	0
Ending Fair Value	0	36	5	35
RMBS \| Fixed maturity AFS securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	13	1	1
Items Included in Net Income	0	0
Gains (Losses) in OCI and Other	(1)	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	0
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	12	1	13	1
CMBS \| Fixed maturity AFS securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	8
Items Included in Net Income	0
Gains (Losses) in OCI and Other	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0
Transfers Into or Out of Level 3, Net	0
Ending Fair Value	8		8
ABS \| Fixed maturity AFS securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	1,484	1,117	1,117
Items Included in Net Income	1	0
Gains (Losses) in OCI and Other	(2)	8
Issuances, Sales, Maturities, Settlements, Calls, Net	201	168
Transfers Into or Out of Level 3, Net	8	(193)
Ending Fair Value	1,692	1,100	1,484	1,117
Hybrid and redeemable preferred securities \| Fixed maturity AFS securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	48	49	49
Items Included in Net Income	0	0
Gains (Losses) in OCI and Other	3	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	(2)
Transfers Into or Out of Level 3, Net	0	12
Ending Fair Value	51	59	48	49
Trading securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	284	581	581
Items Included in Net Income	0	4
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	(13)	(127)
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	271	458	284	581
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	42	153	153
Items Included in Net Income	(3)	(16)
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	0
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	39	137	42	153
Mortgage loans on real estate
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	288	487	487
Items Included in Net Income	0	2
Gains (Losses) in OCI and Other	1	3
Issuances, Sales, Maturities, Settlements, Calls, Net	0	(2)
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	289	490	288	487
Derivative investments
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	36	2	2
Items Included in Net Income	12	(1)
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	4	0
Transfers Into or Out of Level 3, Net	(51)	0
Ending Fair Value	1	1	36	2
Ceded MRBs \| Other assets
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	274	539	539
Items Included in Net Income	(215)	160
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	0
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	59	699	274	539
Ceded MRBs \| Other liabilities
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	(1,149)	(246)	(246)
Items Included in Net Income	(1,112)	(663)
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	0
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	(2,261)	(909)	(1,149)	(246)
Indexed annuity ceded embedded derivatives \| Other assets
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	940	525	525
Items Included in Net Income	33	6
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	(226)
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	973	305	940	525
Indexed annuity ceded embedded derivatives \| Policyholder account balances
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	(9,077)	(4,783)	(4,783)
Items Included in Net Income	(1,677)	(719)
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	(142)	(294)
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	(10,896)	(5,796)	(9,077)	(4,783)
LPR ceded derivative \| Other assets
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	206	212	212
Items Included in Net Income	(5)	(13)
Gains (Losses) in OCI and Other	0	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0	0
Transfers Into or Out of Level 3, Net	0	0
Ending Fair Value	201	$ 199	206	$ 212
Reinsurance-related embedded derivatives
Fair Value, Assets and Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Abstract]
Beginning Fair Value	0
Items Included in Net Income	(25)
Gains (Losses) in OCI and Other	0
Issuances, Sales, Maturities, Settlements, Calls, Net	0
Transfers Into or Out of Level 3, Net	0
Ending Fair Value	$ (25)		$ 0

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- Definition

Amount of gain (loss) recognized in income from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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- Definition

Amount of gain (loss) recognized in other comprehensive income (OCI) from asset measured at fair value on recurring basis using unobservable input (level 3).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(1a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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- Definition

Amount of purchases, (sales), issuances and (settlements) of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 10
-Topic 820
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

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- Definition

Amount of transfers of financial instrument classified as a derivative asset (liability) after deduction of derivative liability (asset) into (out of) level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

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- Definition

Fair value of financial instrument classified as derivative asset (liability) after deduction of derivative liability (asset), measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-SubTopic 10
-Topic 820
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-3

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- Definition

Indicates line item in statement in which net income is reported that includes gain (loss) from asset measured at fair value using unobservable input (level 3).

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- Definition

Indicates line item in statement in which other comprehensive income (OCI) is reported that includes gain (loss) from asset measured at fair value using unobservable input (level 3).

+ References

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