Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 3,133	$ 4,055	$ 3,481	$ 4,151
Net Realized and Unrealized Gains (Losses) Included in Income	20	21	24	20
Other Comprehensive Income (Loss)	21	(22)	65	34
Purchases, Sales, Issuances and Settlements, Net	264	(202)	138	(440)
Gross Transfers In	52	437	99	552
Gross Transfers Out	(33)	(52)	(350)	(67)
Other	0	44	0	31
Fair Value End of Period	3,457	4,281	3,457	4,281
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	2	0	7	(12)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 1	$ (29)	$ 34	$ 27
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 Beginning of Year	$ (104)	$ (94)	$ (104)	$ (94)	$ 21	$ (28)	$ (210)	$ (479)
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]	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	$ 2,722	$ 3,487	$ 3,010	$ 3,439
Net Realized and Unrealized Gains (Losses) Included in Income	15	23	14	32
Other Comprehensive Income (Loss)	21	(22)	65	34
Purchases, Sales, Issuances and Settlements, Net	262	(162)	155	(293)
Gross Transfers In	49	435	56	550
Gross Transfers Out	(33)	(50)	(264)	(51)
Other	(21)	44	(21)	44
Fair Value End of Period	3,015	3,755	3,015	3,755
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	1	(29)	34	27
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	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	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	(1)	0	(1)	0
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	6	7	6	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	115	383	240	323
Net Realized and Unrealized Gains (Losses) Included in Income	1	0	(8)	1
Other Comprehensive Income (Loss)	1	(2)	11	(2)
Purchases, Sales, Issuances and Settlements, Net	(26)	(22)	(151)	(60)
Gross Transfers In	49	36	49	134
Gross Transfers Out	(31)	(36)	(32)	(37)
Other	38	0	38	0
Fair Value End of Period	147	359	147	359
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	(6)	(2)	0	(1)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,656	1,766	1,894	1,792
Net Realized and Unrealized Gains (Losses) Included in Income	8	24	15	47
Other Comprehensive Income (Loss)	9	(29)	42	(2)
Purchases, Sales, Issuances and Settlements, Net	(39)	(75)	(96)	(150)
Gross Transfers In	0	287	3	287
Gross Transfers Out	(1)	(1)	(225)	(2)
Other	0	44	0	44
Fair Value End of Period	1,633	2,016	1,633	2,016
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	(2)	(30)	15	(2)
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	26	43	26	25
Net Realized and Unrealized Gains (Losses) Included in Income	1	(4)	1	(4)
Other Comprehensive Income (Loss)	1	6	1	6
Purchases, Sales, Issuances and Settlements, Net	(1)	(18)	(5)	(18)
Gross Transfers In	0	68	4	85
Gross Transfers Out	(1)	(1)	(1)	0
Other	0	0	0	0
Fair Value End of Period	26	94	26	94
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	1
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	915	1,284	840	1,289
Net Realized and Unrealized Gains (Losses) Included in Income	5	3	6	(12)
Other Comprehensive Income (Loss)	10	3	11	32
Purchases, Sales, Issuances and Settlements, Net	329	(47)	408	(66)
Gross Transfers In	0	44	0	44
Gross Transfers Out	0	(12)	(6)	(12)
Other	(59)	0	(59)	0
Fair Value End of Period	1,200	1,275	1,200	1,275
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	9	3	19	29
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	171	243	164	234
Net Realized and Unrealized Gains (Losses) Included in Income	2	2	6	1
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(1)	(5)	(6)	5
Gross Transfers In	2	2	33	2
Gross Transfers Out	0	(2)	(23)	(2)
Other	0	(2)	0	(2)
Fair Value End of Period	174	238	174	238
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	1	6	(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 | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1	46	1	45
Net Realized and Unrealized Gains (Losses) Included in Income	0	1	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	(3)	0	(2)
Fair Value End of Period	1	44	1	44
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
Other bond securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	50	53	50	51
Net Realized and Unrealized Gains (Losses) Included in Income	1	0	2	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(1)	(2)	(2)	0
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	(2)	0	(2)
Other	0	0	0	0
Fair Value End of Period	50	49	50	49
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	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	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	120	144	113	138
Net Realized and Unrealized Gains (Losses) Included in Income	1	1	4	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	(3)	(4)	5
Gross Transfers In	2	2	33	2
Gross Transfers Out	0	0	(23)	0
Other	0	1	0	0
Fair Value End of Period	123	145	123	145
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	1	5	(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	35	13	15	14
Net Realized and Unrealized Gains (Losses) Included in Income	3	0	4	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	8	0	18	0
Gross Transfers In	0	0	9	0
Gross Transfers Out	0	0	0	(1)
Other	0	0	0	0
Fair Value End of Period	46	13	46	13
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	2	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	76	183	163	221
Net Realized and Unrealized Gains (Losses) Included in Income	0	(4)	0	(13)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(5)	(36)	(29)	(39)
Gross Transfers In	1	0	1	0
Gross Transfers Out	0	0	(63)	(13)
Other	21	2	21	(11)
Fair Value End of Period	93	145	93	145
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	(1)	(1)	(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	129	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	(113)
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	130	129	130
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