Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Jun. 30, 2024	Dec. 31, 2023	Jun. 30, 2023	Dec. 31, 2022
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 4,281	$ 4,368	$ 4,151	$ 5,062
Net Realized and Unrealized Gains (Losses) Included in Income	(12)	4	8	23
Other Comprehensive Income (Loss)	162	(8)	196	56
Purchases, Sales, Issuances and Settlements, Net	(342)	(167)	(782)	(607)
Gross Transfers In	0	72	552	225
Gross Transfers Out	0	(87)	(67)	(566)
Other	15	10	46	(1)
Fair Value End of Period	4,104	4,192	4,104	4,192
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	5	1	(7)	(41)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 100	$ (37)	$ 56	$ (14)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Adjusted Revenues	Adjusted Revenues	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)	Other comprehensive income (loss)	Other comprehensive income (loss)
Fair Value Beginning of Year	$ 100	$ (925)	$ 100	$ (925)	$ (94)	$ (479)	$ (908)	$ (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]	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	$ 3,755	$ 3,752	$ 3,439	$ 4,475
Net Realized and Unrealized Gains (Losses) Included in Income	(16)	2	16	23
Other Comprehensive Income (Loss)	162	(8)	196	56
Purchases, Sales, Issuances and Settlements, Net	(345)	(161)	(638)	(615)
Gross Transfers In	0	61	550	204
Gross Transfers Out	0	(75)	(51)	(550)
Other	0	9	44	(13)
Fair Value End of Period	3,556	3,580	3,556	3,580
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	100	(37)	56	(14)
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	4	16	3	20
Net Realized and Unrealized Gains (Losses) Included in Income	0	(1)	0	(1)
Other Comprehensive Income (Loss)	0	0	0	1
Purchases, Sales, Issuances and Settlements, Net	0	(11)	1	(16)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	4	4	4	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	(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	6	7	2
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	0	0	1
Purchases, Sales, Issuances and Settlements, Net	0	(3)	0	(5)
Gross Transfers In	0	0	0	7
Gross Transfers Out	0	0	0	(2)
Other	0	0	0	0
Fair Value End of Period	7	3	7	3
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 | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	359	418	323	879
Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(2)	(2)	(6)
Other Comprehensive Income (Loss)	18	(12)	16	5
Purchases, Sales, Issuances and Settlements, Net	4	(63)	(56)	(410)
Gross Transfers In	0	30	134	138
Gross Transfers Out	0	(16)	(37)	(251)
Other	7	0	7	0
Fair Value End of Period	385	355	385	355
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	14	(13)	9	(9)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,016	1,868	1,792	1,884
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	26	46	85
Other Comprehensive Income (Loss)	110	(15)	108	11
Purchases, Sales, Issuances and Settlements, Net	(23)	(63)	(173)	(81)
Gross Transfers In	0	0	287	0
Gross Transfers Out	0	(3)	(2)	(51)
Other	(7)	7	37	(28)
Fair Value End of Period	2,095	1,820	2,095	1,820
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	63	(16)	3	8
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	94	48	25	207
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	(7)	(5)	(29)
Other Comprehensive Income (Loss)	1	0	7	(1)
Purchases, Sales, Issuances and Settlements, Net	(12)	6	(30)	7
Gross Transfers In	0	31	85	42
Gross Transfers Out	0	(24)	0	(172)
Other	0	0	0	0
Fair Value End of Period	82	54	82	54
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	(5)	0	(15)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,275	1,396	1,289	1,483
Net Realized and Unrealized Gains (Losses) Included in Income	(11)	(14)	(23)	(26)
Other Comprehensive Income (Loss)	33	19	65	39
Purchases, Sales, Issuances and Settlements, Net	(314)	(27)	(380)	(110)
Gross Transfers In	0	0	44	17
Gross Transfers Out	0	(32)	(12)	(74)
Other	0	2	0	15
Fair Value End of Period	983	1,344	983	1,344
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	23	(3)	49	1
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	238	250	234	223
Net Realized and Unrealized Gains (Losses) Included in Income	6	(1)	7	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(3)	(3)	2	13
Gross Transfers In	0	1	2	1
Gross Transfers Out	0	0	(2)	(3)
Other	7	1	5	12
Fair Value End of Period	248	248	248	248
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	5	(2)	4	(36)
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	44	44	45	0
Net Realized and Unrealized Gains (Losses) Included in Income	0	1	1	1
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	44
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	2	0	0	0
Fair Value End of Period	46	45	46	45
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	2	1	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	0	0
Other bond securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	49	52	51	65
Net Realized and Unrealized Gains (Losses) Included in Income	3	0	3	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(2)	(2)	(2)	(17)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	(2)	0
Other	5	0	5	0
Fair Value End of Period	55	50	55	50
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	1	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	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	145	154	138	158
Net Realized and Unrealized Gains (Losses) Included in Income	3	(2)	3	(1)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(1)	(1)	4	(14)
Gross Transfers In	0	1	2	1
Gross Transfers Out	0	0	0	(3)
Other	0	1	0	12
Fair Value End of Period	147	153	147	153
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	3	(4)	1	(30)
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	13	28	14	13
Net Realized and Unrealized Gains (Losses) Included in Income	1	0	1	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	2	(2)	2	2
Gross Transfers In	0	0	0	10
Gross Transfers Out	0	(12)	(1)	(13)
Other	(3)	0	(3)	0
Fair Value End of Period	13	14	13	14
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 invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	145	227	221	244
Net Realized and Unrealized Gains (Losses) Included in Income	(3)	3	(16)	(4)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	5	(2)	(34)	(12)
Gross Transfers In	0	10	0	10
Gross Transfers Out	0	0	(13)	0
Other	11	0	0	0
Fair Value End of Period	158	238	158	238
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	3	(12)	(7)
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	130	111	243	107
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)	1	(114)	5
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	112	129	112
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