Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 3,457	$ 4,281	$ 3,481	$ 4,151
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	(12)	23	8
Other Comprehensive Income (Loss)	7	162	72	196
Purchases, Sales, Issuances and Settlements, Net	287	(342)	425	(782)
Gross Transfers In	9	0	108	552
Gross Transfers Out	(26)	0	(376)	(67)
Other	0	15	0	46
Fair Value End of Period	3,733	4,104	3,733	4,104
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	3	5	10	(7)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 17	$ 100	$ 51	$ 56
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	Revenues	Revenues
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Asset, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive income	Other comprehensive income	Other comprehensive income	Other comprehensive income
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 3,015	$ 3,755	$ 3,010	$ 3,439
Net Realized and Unrealized Gains (Losses) Included in Income	1	(16)	15	16
Other Comprehensive Income (Loss)	7	162	72	196
Purchases, Sales, Issuances and Settlements, Net	264	(345)	419	(638)
Gross Transfers In	1	0	57	550
Gross Transfers Out	(24)	0	(288)	(51)
Other	0	0	(21)	44
Fair Value End of Period	3,264	3,556	3,264	3,556
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	17	100	51	56
Bonds available for sale | Obligations of states, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	3	4	3	3
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	1
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	3	4	3	4
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	(5)
Bonds available for sale | Non-U.S. governments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	6	7	7	7
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	(1)	0
Gross Transfers In	1	0	1	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	7	7	7	7
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Bonds available for sale | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	147	359	240	323
Net Realized and Unrealized Gains (Losses) Included in Income	(2)	(3)	(10)	(2)
Other Comprehensive Income (Loss)	(15)	18	(4)	16
Purchases, Sales, Issuances and Settlements, Net	(4)	4	(155)	(56)
Gross Transfers In	0	0	49	134
Gross Transfers Out	(6)	0	(38)	(37)
Other	0	7	38	7
Fair Value End of Period	120	385	120	385
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(13)	14	(13)	9
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,633	2,016	1,894	1,792
Net Realized and Unrealized Gains (Losses) Included in Income	7	(1)	22	46
Other Comprehensive Income (Loss)	8	110	50	108
Purchases, Sales, Issuances and Settlements, Net	(5)	(23)	(101)	(173)
Gross Transfers In	0	0	3	287
Gross Transfers Out	(17)	0	(242)	(2)
Other	0	(7)	0	37
Fair Value End of Period	1,626	2,095	1,626	2,095
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	15	63	30	3
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	26	94	26	25
Net Realized and Unrealized Gains (Losses) Included in Income	(5)	(1)	(4)	(5)
Other Comprehensive Income (Loss)	5	1	6	7
Purchases, Sales, Issuances and Settlements, Net	(4)	(12)	(9)	(30)
Gross Transfers In	0	0	4	85
Gross Transfers Out	0	0	(1)	0
Other	0	0	0	0
Fair Value End of Period	22	82	22	82
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	5	0	5	0
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,200	1,275	840	1,289
Net Realized and Unrealized Gains (Losses) Included in Income	1	(11)	7	(23)
Other Comprehensive Income (Loss)	9	33	20	65
Purchases, Sales, Issuances and Settlements, Net	277	(314)	685	(380)
Gross Transfers In	0	0	0	44
Gross Transfers Out	(1)	0	(7)	(12)
Other	0	0	(59)	0
Fair Value End of Period	1,486	983	1,486	983
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	10	23	29	49
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	174	238	164	234
Net Realized and Unrealized Gains (Losses) Included in Income	1	6	7	7
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	13	(3)	7	2
Gross Transfers In	0	0	33	2
Gross Transfers Out	(2)	0	(25)	(2)
Other	0	7	0	5
Fair Value End of Period	186	248	186	248
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	4	5	10	4
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1	44	1	45
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	1
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	0
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	2	0	0
Fair Value End of Period	1	46	1	46
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	2	0	1
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	50	49	50	51
Net Realized and Unrealized Gains (Losses) Included in Income	0	3	2	3
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	3	(2)	1	(2)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	(2)
Other	0	5	0	5
Fair Value End of Period	53	55	53	55
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	1	2
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other bond securities | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	123	145	113	138
Net Realized and Unrealized Gains (Losses) Included in Income	1	3	5	3
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	10	(1)	6	4
Gross Transfers In	0	0	33	2
Gross Transfers Out	(2)	0	(25)	0
Other	0	0	0	0
Fair Value End of Period	132	147	132	147
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	4	3	9	1
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	46	13	15	14
Net Realized and Unrealized Gains (Losses) Included in Income	2	1	6	1
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	5	2	23	2
Gross Transfers In	8	0	17	0
Gross Transfers Out	0	0	0	(1)
Other	0	(3)	0	(3)
Fair Value End of Period	61	13	61	13
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	2	1
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	93	145	163	221
Net Realized and Unrealized Gains (Losses) Included in Income	(5)	(3)	(5)	(16)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	5	5	(24)	(34)
Gross Transfers In	0	0	1	0
Gross Transfers Out	0	0	(63)	(13)
Other	0	11	21	0
Fair Value End of Period	93	158	93	158
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	0	(2)	(12)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	129	130	129	243
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	(1)	0	(114)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	129	129	129	129
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 0	$ 0	$ 0	$ 0