Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 4,151	$ 5,062
Net Realized and Unrealized Gains (Losses) Included in Income	6	48
Other Comprehensive Income (Loss)	96	73
Purchases, Sales, Issuances and Settlements, Net	(926)	(790)
Gross Transfers In	705	329
Gross Transfers Out	(601)	(599)
Other	50	28
Fair Value End of Period	3,481	4,151
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(9)	(31)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ (16)	$ (29)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Adjusted Revenues	Adjusted 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 (loss)	Other comprehensive income (loss)
Fair Value Beginning of Year	$ (28)	$ (479)	$ (512)
Net realized gains/(losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value, Asset, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total net realized gains (losses)	Total net realized gains (losses)
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 3,439	$ 4,475
Net Realized and Unrealized Gains (Losses) Included in Income	19	35
Other Comprehensive Income (Loss)	96	73
Purchases, Sales, Issuances and Settlements, Net	(782)	(885)
Gross Transfers In	691	308
Gross Transfers Out	(495)	(583)
Other	42	16
Fair Value End of Period	3,010	3,439
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	(16)	(29)
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	20
Net Realized and Unrealized Gains (Losses) Included in Income	0	(1)
Other Comprehensive Income (Loss)	0	1
Purchases, Sales, Issuances and Settlements, Net	0	(16)
Gross Transfers In	0	0
Gross Transfers Out	0	(1)
Other	0	0
Fair Value End of Period	3	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	(5)	0
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	7	2
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	1
Purchases, Sales, Issuances and Settlements, Net	0	(5)
Gross Transfers In	0	11
Gross Transfers Out	0	(2)
Other	0	0
Fair Value End of Period	7	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	0	1
Bonds available for sale | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	323	879
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	(8)
Other Comprehensive Income (Loss)	(3)	11
Purchases, Sales, Issuances and Settlements, Net	(71)	(537)
Gross Transfers In	232	236
Gross Transfers Out	(245)	(258)
Other	5	0
Fair Value End of Period	240	323
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	(6)	(5)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,792	1,884
Net Realized and Unrealized Gains (Losses) Included in Income	53	114
Other Comprehensive Income (Loss)	32	(10)
Purchases, Sales, Issuances and Settlements, Net	(238)	(142)
Gross Transfers In	308	0
Gross Transfers Out	(89)	(54)
Other	36	0
Fair Value End of Period	1,894	1,792
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	(43)	(17)
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	25	207
Net Realized and Unrealized Gains (Losses) Included in Income	(11)	(31)
Other Comprehensive Income (Loss)	13	4
Purchases, Sales, Issuances and Settlements, Net	(32)	(6)
Gross Transfers In	108	44
Gross Transfers Out	(78)	(193)
Other	1	0
Fair Value End of Period	26	25
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	(11)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,289	1,483
Net Realized and Unrealized Gains (Losses) Included in Income	(22)	(39)
Other Comprehensive Income (Loss)	54	66
Purchases, Sales, Issuances and Settlements, Net	(441)	(179)
Gross Transfers In	43	17
Gross Transfers Out	(83)	(75)
Other	0	16
Fair Value End of Period	840	1,289
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	37	3
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	234	223
Net Realized and Unrealized Gains (Losses) Included in Income	2	9
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	1	(8)
Gross Transfers In	3	1
Gross Transfers Out	(80)	(3)
Other	4	12
Fair Value End of Period	164	234
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	(31)
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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	45	0
Net Realized and Unrealized Gains (Losses) Included in Income	0	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	44
Gross Transfers In	1	0
Gross Transfers Out	(45)	0
Other	0	0
Fair Value End of Period	1	45
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	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
Other bond securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	51	65
Net Realized and Unrealized Gains (Losses) Included in Income	1	4
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(3)	(18)
Gross Transfers In	0	0
Gross Transfers Out	(3)	0
Other	4	0
Fair Value End of Period	50	51
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	2	(7)
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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	138	158
Net Realized and Unrealized Gains (Losses) Included in Income	1	4
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	4	(34)
Gross Transfers In	2	1
Gross Transfers Out	(32)	(3)
Other	0	12
Fair Value End of Period	113	138
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	(25)
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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	14	13
Net Realized and Unrealized Gains (Losses) Included in Income	1	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	4	3
Gross Transfers In	11	10
Gross Transfers Out	(13)	(13)
Other	(2)	0
Fair Value End of Period	15	14
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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	221	244
Net Realized and Unrealized Gains (Losses) Included in Income	(16)	3
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(35)	(36)
Gross Transfers In	0	10
Gross Transfers Out	(13)	0
Other	6	0
Fair Value End of Period	163	221
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(11)	(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 assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	243	107
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(114)	136
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	129	243
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