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	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	$ 30,571	$ 24,347	$ 26,627	$ 23,588
Net Realized and Unrealized Gains (Losses) Included in Income	358	120	657	205
Other Comprehensive Income (Loss)	680	(384)	872	(40)
Purchases, Sales, Issuances and Settlements, Net	1,106	495	4,328	1,579
Gross Transfers In	450	769	1,918	1,178
Gross Transfers Out	(316)	(222)	(1,535)	(1,614)
Other	(7)	116	(25)	345
Fair Value End of Period	32,842	25,241	32,842	25,241
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	58	(25)	4	(81)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	662	(403)	744	(294)
Market risk benefit assets, at fair value	1,164		1,164		$ 912
Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	1,164		1,164		912
Level 3 | Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	1,164	978	1,164	978	$ 912
Bonds available-for-sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	27,298	21,249	23,412	20,426
Net Realized and Unrealized Gains (Losses) Included in Income	284	139	612	253
Other Comprehensive Income (Loss)	665	(371)	868	(34)
Purchases, Sales, Issuances and Settlements, Net	962	397	4,043	1,340
Gross Transfers In	446	734	1,892	1,104
Gross Transfers Out	(307)	(220)	(1,477)	(1,336)
Other	0	72	(2)	247
Fair Value End of Period	29,348	22,000	29,348	22,000
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	662	(403)	744	(294)
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 Year	796	853	844	805
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	(2)	(1)	(2)
Other Comprehensive Income (Loss)	55	(77)	8	(26)
Purchases, Sales, Issuances and Settlements, Net	0	(12)	(1)	(15)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	850	762	850	762
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	53	(81)	4	(54)
Bonds available-for-sale | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	1,393	1,303	1,357	1,968
Net Realized and Unrealized Gains (Losses) Included in Income	8	(3)	9	(95)
Other Comprehensive Income (Loss)	44	(65)	47	(23)
Purchases, Sales, Issuances and Settlements, Net	(46)	(13)	(116)	(40)
Gross Transfers In	241	147	668	358
Gross Transfers Out	(89)	(185)	(414)	(968)
Other	0	0	0	(16)
Fair Value End of Period	1,551	1,184	1,551	1,184
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	46	(70)	5	(52)
Bonds available-for-sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	6,453	5,753	5,854	5,670
Net Realized and Unrealized Gains (Losses) Included in Income	82	74	224	230
Other Comprehensive Income (Loss)	242	(66)	218	27
Purchases, Sales, Issuances and Settlements, Net	(20)	(13)	592	(195)
Gross Transfers In	0	1	21	33
Gross Transfers Out	(144)	(22)	(294)	(38)
Other	0	0	(2)	0
Fair Value End of Period	6,613	5,727	6,613	5,727
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	234	(106)	211	(41)
Bonds available-for-sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	529	505	608	718
Net Realized and Unrealized Gains (Losses) Included in Income	13	5	11	5
Other Comprehensive Income (Loss)	52	(28)	101	(69)
Purchases, Sales, Issuances and Settlements, Net	(27)	(2)	(154)	(42)
Gross Transfers In	118	33	245	57
Gross Transfers Out	(9)	0	(135)	(156)
Other	0	0	0	0
Fair Value End of Period	676	513	676	513
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	40	(27)	45	(98)
Bonds available-for-sale | CLO
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	1,772	1,708	1,843	1,670
Net Realized and Unrealized Gains (Losses) Included in Income	34	24	31	(21)
Other Comprehensive Income (Loss)	(39)	32	20	58
Purchases, Sales, Issuances and Settlements, Net	326	(40)	404	(85)
Gross Transfers In	10	2	42	67
Gross Transfers Out	(63)	(11)	(300)	(165)
Other	0	72	0	263
Fair Value End of Period	2,040	1,787	2,040	1,787
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	(26)	34	20	(13)
Bonds available-for-sale | ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	16,355	11,127	12,906	9,595
Net Realized and Unrealized Gains (Losses) Included in Income	148	41	338	136
Other Comprehensive Income (Loss)	311	(167)	474	(1)
Purchases, Sales, Issuances and Settlements, Net	729	477	3,318	1,717
Gross Transfers In	77	551	916	589
Gross Transfers Out	(2)	(2)	(334)	(9)
Other	0	0	0	0
Fair Value End of Period	17,618	12,027	17,618	12,027
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	315	(153)	459	(36)
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	1,570	1,140	1,323	1,304
Net Realized and Unrealized Gains (Losses) Included in Income	57	(2)	109	32
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	14	25	192	3
Gross Transfers In	4	0	26	39
Gross Transfers Out	(9)	(2)	(14)	(271)
Other	0	44	0	98
Fair Value End of Period	1,636	1,205	1,636	1,205
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	43	(11)	76	(4)
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 | Obligations of states, municipalities and political subdivisions
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	1	3	1	0
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	(2)	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	1	1	1	1
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 | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	195	110	167	417
Net Realized and Unrealized Gains (Losses) Included in Income	7	1	23	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	65	10	(51)
Gross Transfers In	3	0	5	0
Gross Transfers Out	0	0	0	(192)
Other	0	0	0	0
Fair Value End of Period	205	176	205	176
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	7	3	23	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 bond securities | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	103	112	107	107
Net Realized and Unrealized Gains (Losses) Included in Income	5	(4)	7	2
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(1)	(2)	(7)	(3)
Gross Transfers In	0	0	0	0
Gross Transfers Out	(2)	0	(2)	0
Other	0	0	0	0
Fair Value End of Period	105	106	105	106
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	4	(4)	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
Other bond securities | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	17	26	17	28
Net Realized and Unrealized Gains (Losses) Included in Income	1	(2)	1	(4)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(4)	0	(4)	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	14	24	14	24
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	1	(3)	1	(4)
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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	61	25	69	11
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	5	(1)	14
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	8	(3)	1	(49)
Gross Transfers In	0	0	0	39
Gross Transfers Out	(7)	(2)	(8)	(44)
Other	0	44	0	0
Fair Value End of Period	61	69	61	69
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	3	0	3
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 | ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	1,193	864	962	741
Net Realized and Unrealized Gains (Losses) Included in Income	45	(2)	79	18
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	11	(33)	192	105
Gross Transfers In	1	0	21	0
Gross Transfers Out	0	0	(4)	(35)
Other	0	0	0	98
Fair Value End of Period	1,250	829	1,250	829
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	32	(10)	47	(4)
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 Year	48	44	42	26
Net Realized and Unrealized Gains (Losses) Included in Income	0	0	1	0
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	1	5	26
Gross Transfers In	0	1	0	1
Gross Transfers Out	0	0	0	(7)
Other	(7)	0	(7)	0
Fair Value End of Period	41	46	41	46
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 invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Year	1,655	1,914	1,850	1,832
Net Realized and Unrealized Gains (Losses) Included in Income	17	(17)	(65)	(80)
Other Comprehensive Income (Loss)	15	(13)	4	(6)
Purchases, Sales, Issuances and Settlements, Net	130	72	88	210
Gross Transfers In	0	34	0	34
Gross Transfers Out	0	0	(44)	0
Other	0	0	(16)	0
Fair Value End of Period	1,817	1,990	1,817	1,990
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	15	(14)	(72)	(77)
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