Fair Value Measurements - Changes in level 3 recurring fair value measurements, assets (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 29,622	$ 30,861	$ 31,627	$ 31,578
Net Realized and Unrealized Gains (Losses) Included in Income	64	351	265	1,024
Other Comprehensive Income (Loss)	(936)	(64)	(3,601)	(74)
Purchases, Sales, Issuances and Settlements, Net	(42)	(601)	1,201	(2,084)
Gross Transfers In	2,217	130	4,414	1,506
Gross Transfers Out	(571)	(493)	(3,552)	(1,766)
Other	0	(62)	0	(62)
Fair Value End of Period	30,354	30,122	30,354	30,122
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(90)	141	(140)	540
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(868)	0	(2,835)	1,433
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	24,368	26,207	26,862	26,889
Net Realized and Unrealized Gains (Losses) Included in Income	43	149	273	518
Other Comprehensive Income (Loss)	(911)	(62)	(3,549)	(65)
Purchases, Sales, Issuances and Settlements, Net	61	(99)	853	(1,179)
Gross Transfers In	2,162	129	4,027	1,423
Gross Transfers Out	(513)	(493)	(3,256)	(1,755)
Other	0	(62)	0	(62)
Fair Value End of Period	25,210	25,769	25,210	25,769
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	(868)	0	(2,835)	1,433
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	957	1,939	1,431	2,105
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	6	1	14
Other Comprehensive Income (Loss)	(106)	(9)	(534)	(40)
Purchases, Sales, Issuances and Settlements, Net	(29)	(7)	(94)	(125)
Gross Transfers In	0	0	17	0
Gross Transfers Out	(7)	(61)	(7)	(86)
Other	0	(62)	0	(62)
Fair Value End of Period	814	1,806	814	1,806
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	(167)	0	(319)	225
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	9	10	7	5
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	(1)	0	(1)	1
Gross Transfers In	1	0	3	5
Gross Transfers Out	0	(3)	0	(3)
Other	0	0	0	0
Fair Value End of Period	9	7	9	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	2,483	2,773	2,641	2,349
Net Realized and Unrealized Gains (Losses) Included in Income	(31)	(1)	(57)	12
Other Comprehensive Income (Loss)	(53)	2	(204)	9
Purchases, Sales, Issuances and Settlements, Net	(100)	(173)	(137)	35
Gross Transfers In	1,781	57	2,163	452
Gross Transfers Out	(163)	(12)	(489)	(211)
Other	0	0	0	0
Fair Value End of Period	3,917	2,646	3,917	2,646
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	(55)	0	(183)	(106)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	8,352	11,085	10,378	11,694
Net Realized and Unrealized Gains (Losses) Included in Income	101	118	323	435
Other Comprehensive Income (Loss)	(267)	(8)	(1,210)	17
Purchases, Sales, Issuances and Settlements, Net	(299)	(86)	(1,173)	(977)
Gross Transfers In	2	8	2	8
Gross Transfers Out	(8)	(19)	(439)	(79)
Other	0	0	0	0
Fair Value End of Period	7,881	11,098	7,881	11,098
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	(39)	0	(704)	934
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	871	1,082	1,190	922
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	4	12	20
Other Comprehensive Income (Loss)	(31)	(6)	(144)	(39)
Purchases, Sales, Issuances and Settlements, Net	(33)	(13)	84	245
Gross Transfers In	12	0	12	56
Gross Transfers Out	(12)	(42)	(348)	(179)
Other	0	0	0	0
Fair Value End of Period	806	1,025	806	1,025
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	(50)	0	(143)	(45)
Bonds available for sale | CDO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	11,696	9,318	11,215	9,814
Net Realized and Unrealized Gains (Losses) Included in Income	(25)	22	(6)	37
Other Comprehensive Income (Loss)	(454)	(41)	(1,457)	(11)
Purchases, Sales, Issuances and Settlements, Net	523	180	2,174	(358)
Gross Transfers In	366	64	1,830	902
Gross Transfers Out	(323)	(356)	(1,973)	(1,197)
Other	0	0	0	0
Fair Value End of Period	11,783	9,187	11,783	9,187
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	(557)	0	(1,486)	425
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	3,127	2,438	2,697	2,698
Net Realized and Unrealized Gains (Losses) Included in Income	(40)	41	(314)	78
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(66)	(151)	424	(454)
Gross Transfers In	40	0	325	6
Gross Transfers Out	(16)	0	(87)	0
Other	0	0	0	0
Fair Value End of Period	3,045	2,328	3,045	2,328
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(110)	0	(456)	151
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	461		134
Net Realized and Unrealized Gains (Losses) Included in Income	(5)		(9)
Other Comprehensive Income (Loss)	0		0
Purchases, Sales, Issuances and Settlements, Net	66		190
Gross Transfers In	28		250
Gross Transfers Out	(1)		(16)
Other	0		0
Fair Value End of Period	549		549
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(7)		(8)
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	192	113	196	139
Net Realized and Unrealized Gains (Losses) Included in Income	(7)	2	(25)	6
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	26	(8)	40	(38)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	211	107	211	107
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(8)	0	(28)	(86)
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 Period	32	46	35	47
Net Realized and Unrealized Gains (Losses) Included in Income	(3)	(1)	(6)	(2)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	(9)	0	(15)
Gross Transfers In	0	0	0	6
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	29	36	29	36
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(3)	0	(6)	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 | CDO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,442	2,279	2,332	2,512
Net Realized and Unrealized Gains (Losses) Included in Income	(25)	40	(274)	74
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	(158)	(134)	194	(401)
Gross Transfers In	12	0	75	0
Gross Transfers Out	(15)	0	(71)	0
Other	0	0	0	0
Fair Value End of Period	2,256	2,185	2,256	2,185
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(92)	0	(414)	235
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	12	4	6	51
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	0	(1)	11
Other Comprehensive Income (Loss)	0	1	0	1
Purchases, Sales, Issuances and Settlements, Net	8	(1)	14	(124)
Gross Transfers In	15	1	15	77
Gross Transfers Out	0	0	0	(11)
Other	0	0	0	0
Fair Value End of Period	34	5	34	5
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	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 invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,008	2,099	1,948	1,827
Net Realized and Unrealized Gains (Losses) Included in Income	62	161	307	417
Other Comprehensive Income (Loss)	(25)	(3)	(52)	(10)
Purchases, Sales, Issuances and Settlements, Net	(45)	(351)	(83)	(328)
Gross Transfers In	0	0	47	0
Gross Transfers Out	(42)	0	(209)	0
Other	0	0	0	0
Fair Value End of Period	1,958	1,906	1,958	1,906
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	20	141	316	386
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	107	113	114	113
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	(7)	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	107	114	107	114
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