Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024
Assets:
Fair Value Beginning of Period	$ 3,481	$ 4,151
Net Realized and Unrealized Gains (Losses) Included in Income	18	6
Other Comprehensive Income (Loss)	27	96
Purchases, Sales, Issuances and Settlements, Net	759	(926)
Gross Transfers In	184	705
Gross Transfers Out	(568)	(601)
Other	(3)	50
Fair Value End of Period	3,898	3,481
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	11	(9)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 44	$ (16)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	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
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)
Bonds available for sale
Assets:
Fair Value Beginning of Period	$ 3,010	$ 3,439
Net Realized and Unrealized Gains (Losses) Included in Income	12	19
Other Comprehensive Income (Loss)	27	96
Purchases, Sales, Issuances and Settlements, Net	772	(782)
Gross Transfers In	133	691
Gross Transfers Out	(481)	(495)
Other	(22)	42
Fair Value End of Period	3,451	3,010
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	44	(16)
Bonds available for sale | Obligations of states, municipalities and political subdivisions
Assets:
Fair Value Beginning of Period	3	3
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	1	0
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	4	3
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	1	(5)
Bonds available for sale | Non-U.S. governments
Assets:
Fair Value Beginning of Period	7	7
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0
Gross Transfers In	16	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	23	7
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	3	0
Bonds available for sale | Corporate debt
Assets:
Fair Value Beginning of Period	240	323
Net Realized and Unrealized Gains (Losses) Included in Income	(19)	(1)
Other Comprehensive Income (Loss)	(1)	(3)
Purchases, Sales, Issuances and Settlements, Net	(169)	(71)
Gross Transfers In	109	232
Gross Transfers Out	(85)	(245)
Other	38	5
Fair Value End of Period	113	240
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	27	(6)
Bonds available for sale | RMBS
Assets:
Fair Value Beginning of Period	1,894	1,792
Net Realized and Unrealized Gains (Losses) Included in Income	27	53
Other Comprehensive Income (Loss)	6	32
Purchases, Sales, Issuances and Settlements, Net	(141)	(238)
Gross Transfers In	2	308
Gross Transfers Out	(242)	(89)
Other	0	36
Fair Value End of Period	1,546	1,894
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(7)	(43)
Bonds available for sale | CMBS
Assets:
Fair Value Beginning of Period	26	25
Net Realized and Unrealized Gains (Losses) Included in Income	(4)	(11)
Other Comprehensive Income (Loss)	5	13
Purchases, Sales, Issuances and Settlements, Net	(9)	(32)
Gross Transfers In	6	108
Gross Transfers Out	0	(78)
Other	0	1
Fair Value End of Period	24	26
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	1	1
Bonds available for sale | CLO/ABS
Assets:
Fair Value Beginning of Period	840	1,289
Net Realized and Unrealized Gains (Losses) Included in Income	8	(22)
Other Comprehensive Income (Loss)	17	54
Purchases, Sales, Issuances and Settlements, Net	1,090	(441)
Gross Transfers In	0	43
Gross Transfers Out	(154)	(83)
Other	(60)	0
Fair Value End of Period	1,741	840
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	19	37
Other bond securities
Assets:
Fair Value Beginning of Period	164	234
Net Realized and Unrealized Gains (Losses) Included in Income	5	2
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(7)	1
Gross Transfers In	32	3
Gross Transfers Out	(24)	(80)
Other	0	4
Fair Value End of Period	170	164
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	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
Other bond securities | Corporate debt
Assets:
Fair Value Beginning of Period	1	45
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0
Gross Transfers In	0	1
Gross Transfers Out	0	(45)
Other	0	0
Fair Value End of Period	0	1
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other bond securities | RMBS
Assets:
Fair Value Beginning of Period	50	51
Net Realized and Unrealized Gains (Losses) Included in Income	2	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	(3)
Gross Transfers In	1	0
Gross Transfers Out	(2)	(3)
Other	0	4
Fair Value End of Period	51	50
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	2	2
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other bond securities | CLO/ABS
Assets:
Fair Value Beginning of Period	113	138
Net Realized and Unrealized Gains (Losses) Included in Income	4	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(7)	4
Gross Transfers In	31	2
Gross Transfers Out	(22)	(32)
Other	0	0
Fair Value End of Period	119	113
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	8	(1)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Equity securities
Assets:
Fair Value Beginning of Period	15	14
Net Realized and Unrealized Gains (Losses) Included in Income	4	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	18	4
Gross Transfers In	18	11
Gross Transfers Out	0	(13)
Other	0	(2)
Fair Value End of Period	55	15
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	1
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other invested assets
Assets:
Fair Value Beginning of Period	163	221
Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(16)
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(25)	(35)
Gross Transfers In	1	0
Gross Transfers Out	(63)	(13)
Other	19	6
Fair Value End of Period	92	163
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	(11)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other assets
Assets:
Fair Value Beginning of Period	129	243
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	1	(114)
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	130	129
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	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