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		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Corporate bonds and other
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	$ 1,388	$ 1,129	$ 1,278	$ 1,045
Included in Net Income			1
Included in OCI	21	59	58	39
Purchases	24	83	123	229
Sales		(10)		(10)
Settlements	(33)	(24)	(75)	(77)
Transfers into Level 3			15	11
Transfers out of Level 3
Balance at ending of period	1,400	1,237	1,400	1,237
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities	21	57	55	34
States, municipalities and political subdivisions
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	44	43	42	44
Included in Net Income
Included in OCI		2	2	1
Purchases
Sales
Settlements
Transfers into Level 3
Transfers out of Level 3
Balance at ending of period	44	45	44	45
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities		2	2	1
Asset-backed
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	886	887	876	901
Included in Net Income	8	1	13	5
Included in OCI	8	30	5	14
Purchases	93	38	142	111
Sales				(14)
Settlements	(36)	(23)	(77)	(65)
Transfers into Level 3
Transfers out of Level 3		(18)		(37)
Balance at ending of period	959	915	959	915
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities	9	30	6	14
Fixed maturities available-for-sale
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	2,318	2,059	2,196	1,990
Included in Net Income	8	1	14	5
Included in OCI	29	91	65	54
Purchases	117	121	265	340
Sales	0	(10)	0	(24)
Settlements	(69)	(47)	(152)	(142)
Transfers into Level 3	0	0	15	11
Transfers out of Level 3	0	(18)	0	(37)
Balance at ending of period	2,403	2,197	2,403	2,197
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities	0	0	0	0
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities	30	89	63	49
Equity securities
Reconciliations for All Assets and Liabilities [Roll Forward]
Balance at beginning of period	10	14	20	24
Included in Net Income			1	6
Included in OCI
Purchases				3
Sales			(7)	(19)
Settlements			(4)
Transfers into Level 3
Transfers out of Level 3
Balance at ending of period	10	14	10	14
Unrealized Gains (Losses) Recognized in Net Income (Loss) on Level 3 Assets and Liabilities			(1)	2
Unrealized Gains (Losses) Recognized in Other Comprehensive Income (Loss) on Level 3 Assets and Liabilities