Fair Value Measurements (Details) - Changes in Level 3 - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance		$ 675	$ 675	$ 596
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains (losses)			$ (6)	$ 36
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]			Net realized investment gains (losses)	Net realized investment gains (losses)
Level 3 fair value category, total unrealized investment gains (losses) reported in other comprehensive income (loss)			$ 6	$ (13)
Level 3 fair value category purchases			29	233
Level 3 fair value category sales			(1)	(1)
Level 3 fair value category settlements/maturities			(26)	(57)
Gross transfers into Level 3			0	3
Gross transfers out of Level 3			(382)	(122)
Level 3 fair value category, ending balance			295	675
Amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date			$ 0	$ 34
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]			Net realized investment gains (losses)	Net realized investment gains (losses)
Fixed maturities [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance		303	$ 303	$ 248
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains (losses)			(1)	1
Level 3 fair value category, total unrealized investment gains (losses) reported in other comprehensive income (loss)			6	(13)
Level 3 fair value category purchases			25	226
Level 3 fair value category sales			0	0
Level 3 fair value category settlements/maturities			(26)	(55)
Gross transfers into Level 3			0	0
Gross transfers out of Level 3			(49)	(104)
Level 3 fair value category, ending balance			258	303
Amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date			0	0
Equity securities [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance		371	371	343
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains (losses)			(5)	33
Level 3 fair value category, total unrealized investment gains (losses) reported in other comprehensive income (loss)			0	0
Level 3 fair value category purchases			4	7
Level 3 fair value category sales			0	0
Level 3 fair value category settlements/maturities			0	0
Gross transfers into Level 3			0	3
Gross transfers out of Level 3			(333)	(15)
Level 3 fair value category, ending balance			37	371
Amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date			0	33
Common stock [Member]
Changes in Level 3 fair value category [Roll Forward]
Gross transfers out of Level 3	$ (151)	(182)
Other investments [Member]
Changes in Level 3 fair value category [Roll Forward]
Level 3 fair value category, beginning balance		$ 1	1	5
Level 3 fair value category, total realized and unrealized investment gains (losses) reported in net realized investment gains (losses)			0	2
Level 3 fair value category, total unrealized investment gains (losses) reported in other comprehensive income (loss)			0	0
Level 3 fair value category purchases			0	0
Level 3 fair value category sales			(1)	(1)
Level 3 fair value category settlements/maturities			0	(2)
Gross transfers into Level 3			0	0
Gross transfers out of Level 3			0	(3)
Level 3 fair value category, ending balance			0	1
Amount of total realized investment gains (losses) for the period included in the consolidated statement of income attributable to changes in the fair value of assets still held at the reporting date			$ 0	$ 1

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

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

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- Definition

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

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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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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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 of financial instrument classified as an 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 (c)(2)
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-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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Amount of sale of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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Amount of settlement of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

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- Definition

Amount of transfer of financial instrument classified as an asset into level 3 of the fair value hierarchy.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 820
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 2
-Subparagraph (c)(3)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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- Definition

Amount of transfers of financial instrument classified as an asset out of level 3 of the fair value hierarchy.

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Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

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-Topic 820
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-URI https://asc.fasb.org//1943274/2147482106/820-10-50-2

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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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