Fair Value - Reconciliations of Assets and Liabilities Measured at Fair Value on Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Corporate bonds and other
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	$ 1,514	$ 1,351	$ 1,483	$ 1,278
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income		1	(3)	1
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	2	16	(22)	37
Purchases	101	44	164	99
Sales
Settlements	(23)	(24)	(28)	(42)
Transfers into Level 3				15
Transfers out of Level 3
Balance at ending of period	1,594	1,388	1,594	1,388
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at June 30	2	16	(22)	37
States, municipalities and political subdivisions
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	44	44	45	42
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI			(1)	2
Purchases
Sales
Settlements
Transfers into Level 3
Transfers out of Level 3
Balance at ending of period	44	44	44	44
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at June 30			(1)	2
Asset-backed
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	955	889	998	876
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	2	1	4	5
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	(5)	(4)	(21)	(3)
Purchases	42	22	82	49
Sales
Settlements	(26)	(22)	(46)	(41)
Transfers into Level 3
Transfers out of Level 3	(25)		(74)
Balance at ending of period	943	886	943	886
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at June 30	(5)	(4)	(21)	(3)
Fixed maturities available-for-sale
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	2,513	2,284	2,526	2,196
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	2	2	1	6
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI	(3)	12	(44)	36
Purchases	143	66	246	148
Sales	0	0	0	0
Settlements	(49)	(46)	(74)	(83)
Transfers into Level 3	0	0	0	15
Transfers out of Level 3	(25)	0	(74)	0
Balance at ending of period	2,581	2,318	2,581	2,318
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30	0	0	0	0
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at June 30	(3)	12	(44)	36
Equity securities
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	32	17	33	20
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in Net Income	3		2	1
Net Realized Investment Gains (Losses) and Net Change in Unrealized Investment Gains (Losses) Included in OCI
Purchases
Sales	(5)	(7)	(5)	(7)
Settlements				(4)
Transfers into Level 3
Transfers out of Level 3
Balance at ending of period	30	10	30	10
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities Held at June 30		(1)	(1)	(1)
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities Held at June 30

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

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

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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).

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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.

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

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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.

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