Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 4,055	$ 4,990	$ 4,151	$ 5,062
Net Realized and Unrealized Gains (Losses) Included in Income	21	(9)	20	19
Other Comprehensive Income (Loss)	(22)	69	34	64
Purchases, Sales, Issuances and Settlements, Net	(202)	(253)	(440)	(440)
Gross Transfers In	437	9	552	153
Gross Transfers Out	(52)	(412)	(67)	(479)
Other	44	(26)	31	(11)
Fair Value End of Period	4,281	4,368	4,281	4,368
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	(30)	(12)	(40)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ (29)	$ 48	$ 27	$ 29
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)
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	$ 3,487	$ 4,392	$ 3,439	$ 4,475
Net Realized and Unrealized Gains (Losses) Included in Income	23	(11)	32	21
Other Comprehensive Income (Loss)	(22)	69	34	64
Purchases, Sales, Issuances and Settlements, Net	(162)	(268)	(293)	(454)
Gross Transfers In	435	7	550	143
Gross Transfers Out	(50)	(411)	(51)	(475)
Other	44	(26)	44	(22)
Fair Value End of Period	3,755	3,752	3,755	3,752
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	(29)	48	27	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	4	15	3	20
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	1	0	1
Purchases, Sales, Issuances and Settlements, Net	0	0	1	(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	4	16	4	16
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 | Non-U.S. governments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	7	9	7	2
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	0	0
Other Comprehensive Income (Loss)	0	1	0	1
Purchases, Sales, Issuances and Settlements, Net	0	(2)	0	(2)
Gross Transfers In	0	0	0	7
Gross Transfers Out	0	(2)	0	(2)
Other	0	0	0	0
Fair Value End of Period	7	6	7	6
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	1	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	383	728	323	879
Net Realized and Unrealized Gains (Losses) Included in Income	0	(4)	1	(4)
Other Comprehensive Income (Loss)	(2)	10	(2)	17
Purchases, Sales, Issuances and Settlements, Net	(22)	(131)	(60)	(347)
Gross Transfers In	36	1	134	108
Gross Transfers Out	(36)	(186)	(37)	(235)
Other	0	0	0	0
Fair Value End of Period	359	418	359	418
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)	4	(1)	3
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,766	1,896	1,792	1,884
Net Realized and Unrealized Gains (Losses) Included in Income	24	30	47	59
Other Comprehensive Income (Loss)	(29)	56	(2)	26
Purchases, Sales, Issuances and Settlements, Net	(75)	(36)	(150)	(18)
Gross Transfers In	287	0	287	0
Gross Transfers Out	(1)	(43)	(2)	(48)
Other	44	(35)	44	(35)
Fair Value End of Period	2,016	1,868	2,016	1,868
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	(30)	56	(2)	24
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	43	220	25	207
Net Realized and Unrealized Gains (Losses) Included in Income	(4)	(22)	(4)	(22)
Other Comprehensive Income (Loss)	6	(2)	6	(1)
Purchases, Sales, Issuances and Settlements, Net	(18)	0	(18)	1
Gross Transfers In	68	0	85	11
Gross Transfers Out	(1)	(148)	0	(148)
Other	0	0	0	0
Fair Value End of Period	94	48	94	48
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	(4)	1	(12)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,284	1,524	1,289	1,483
Net Realized and Unrealized Gains (Losses) Included in Income	3	(15)	(12)	(12)
Other Comprehensive Income (Loss)	3	3	32	20
Purchases, Sales, Issuances and Settlements, Net	(47)	(99)	(66)	(83)
Gross Transfers In	44	6	44	17
Gross Transfers Out	(12)	(32)	(12)	(42)
Other	0	9	0	13
Fair Value End of Period	1,275	1,396	1,275	1,396
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	3	(9)	29	12
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	243	228	234	223
Net Realized and Unrealized Gains (Losses) Included in Income	2	(1)	1	3
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(5)	23	5	16
Gross Transfers In	2	0	2	0
Gross Transfers Out	(2)	0	(2)	(3)
Other	(2)	0	(2)	11
Fair Value End of Period	238	250	238	250
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	(29)	(1)	(32)
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	46	0	45	0
Net Realized and Unrealized Gains (Losses) Included in Income	1	0	1	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	44	0	44
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	(3)	0	(2)	0
Fair Value End of Period	44	44	44	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	53	52	51	65
Net Realized and Unrealized Gains (Losses) Included in Income	0	2	0	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(2)	(2)	0	(15)
Gross Transfers In	0	0	0	0
Gross Transfers Out	(2)	0	(2)	0
Other	0	0	0	0
Fair Value End of Period	49	52	49	52
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	(4)	0	(9)
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	144	176	138	158
Net Realized and Unrealized Gains (Losses) Included in Income	1	(3)	0	1
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(3)	(19)	5	(13)
Gross Transfers In	2	0	2	0
Gross Transfers Out	0	0	0	(3)
Other	1	0	0	11
Fair Value End of Period	145	154	145	154
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	(25)	(1)	(23)
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	25	14	13
Net Realized and Unrealized Gains (Losses) Included in Income	0	2	0	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	4
Gross Transfers In	0	2	0	10
Gross Transfers Out	0	(1)	(1)	(1)
Other	0	0	0	0
Fair Value End of Period	13	28	13	28
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	2	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	183	235	221	244
Net Realized and Unrealized Gains (Losses) Included in Income	(4)	1	(13)	(7)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(36)	(9)	(39)	(10)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	(13)	0
Other	2	0	(11)	0
Fair Value End of Period	145	227	145	227
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	(3)	(12)	(10)
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	110	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	(113)	4
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	130	111	130	111
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