Fair Value Measurements - Changes in level 3 recurring fair value measurements, assets (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 30,413	$ 31,298	$ 31,627	$ 31,578
Net Realized and Unrealized Gains (Losses) Included in income	65	335	201	673
Other Comprehensive Income (Loss)	(1,180)	168	(2,665)	(10)
Purchases, Sales, Issuances and Settlements, Net	897	(931)	1,243	(1,483)
Gross Transfers In	786	597	2,197	1,376
Gross Transfers Out	(1,359)	(606)	(2,981)	(1,273)
Other	0	0	0	0
Fair Value End of Period	29,622	30,861	29,622	30,861
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	156	393	105	421
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(1,150)	1,672	(2,583)	1,497
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	25,404	26,642	26,862	26,889
Net Realized and Unrealized Gains (Losses) Included in income	85	175	230	369
Other Comprehensive Income (Loss)	(1,159)	172	(2,638)	(3)
Purchases, Sales, Issuances and Settlements, Net	707	(782)	792	(1,080)
Gross Transfers In	619	596	1,865	1,294
Gross Transfers Out	(1,288)	(596)	(2,743)	(1,262)
Other	0	0	0	0
Fair Value End of Period	24,368	26,207	24,368	26,207
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	(1,150)	1,672	(2,583)	1,497
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	1,087	1,896	1,431	2,105
Net Realized and Unrealized Gains (Losses) Included in income	0	5	2	8
Other Comprehensive Income (Loss)	(143)	128	(428)	(31)
Purchases, Sales, Issuances and Settlements, Net	(4)	(65)	(65)	(118)
Gross Transfers In	17	0	17	0
Gross Transfers Out	0	(25)	0	(25)
Other	0	0	0	0
Fair Value End of Period	957	1,939	957	1,939
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	(151)	244	(410)	234
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	8	6	7	5
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	1	0	1
Gross Transfers In	1	4	2	5
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	9	10	9	10
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	2,744	2,570	2,641	2,349
Net Realized and Unrealized Gains (Losses) Included in income	(15)	14	(26)	13
Other Comprehensive Income (Loss)	(78)	17	(151)	7
Purchases, Sales, Issuances and Settlements, Net	(214)	31	(37)	208
Gross Transfers In	252	208	382	395
Gross Transfers Out	(206)	(67)	(326)	(199)
Other	0	0	0	0
Fair Value End of Period	2,483	2,773	2,483	2,773
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	(49)	50	(137)	(109)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	8,925	11,464	10,378	11,694
Net Realized and Unrealized Gains (Losses) Included in income	92	150	222	317
Other Comprehensive Income (Loss)	(390)	(39)	(943)	25
Purchases, Sales, Issuances and Settlements, Net	(266)	(460)	(874)	(891)
Gross Transfers In	0	0	0	0
Gross Transfers Out	(9)	(30)	(431)	(60)
Other	0	0	0	0
Fair Value End of Period	8,352	11,085	8,352	11,085
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	(390)	957	(925)	943
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	864	1,104	1,190	922
Net Realized and Unrealized Gains (Losses) Included in income	5	7	13	16
Other Comprehensive Income (Loss)	(46)	23	(113)	(33)
Purchases, Sales, Issuances and Settlements, Net	85	85	117	258
Gross Transfers In	0	0	0	56
Gross Transfers Out	(37)	(137)	(336)	(137)
Other	0	0	0	0
Fair Value End of Period	871	1,082	871	1,082
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	(47)	18	(108)	(38)
Bonds available for sale | CDO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	11,776	9,602	11,215	9,814
Net Realized and Unrealized Gains (Losses) Included in income	3	(1)	19	15
Other Comprehensive Income (Loss)	(502)	44	(1,003)	30
Purchases, Sales, Issuances and Settlements, Net	1,106	(374)	1,651	(538)
Gross Transfers In	349	384	1,464	838
Gross Transfers Out	(1,036)	(337)	(1,650)	(841)
Other	0	0	0	0
Fair Value End of Period	11,696	9,318	11,696	9,318
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	(513)	403	(1,003)	467
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,960	2,518	2,697	2,698
Net Realized and Unrealized Gains (Losses) Included in income	(153)	46	(274)	37
Other Comprehensive Income (Loss)	1	0	0	0
Purchases, Sales, Issuances and Settlements, Net	209	(126)	490	(303)
Gross Transfers In	167	0	285	6
Gross Transfers Out	(57)	0	(71)	0
Other	0	0	0	0
Fair Value End of Period	3,127	2,438	3,127	2,438
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(18)	271	(190)	173
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	260		134
Net Realized and Unrealized Gains (Losses) Included in income	(4)		(4)
Other Comprehensive Income (Loss)	0		0
Purchases, Sales, Issuances and Settlements, Net	47		124
Gross Transfers In	161		222
Gross Transfers Out	(3)		(15)
Other	0		0
Fair Value End of Period	461		461
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(4)		(4)
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	199	126	196	139
Net Realized and Unrealized Gains (Losses) Included in income	(13)	1	(18)	4
Other Comprehensive Income (Loss)	1	0	0	0
Purchases, Sales, Issuances and Settlements, Net	5	(14)	14	(30)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	192	113	192	113
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(13)	12	(21)	(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	33	46	35	47
Net Realized and Unrealized Gains (Losses) Included in income	(1)	0	(3)	(1)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	(6)
Gross Transfers In	0	0	0	6
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	32	46	32	46
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	6	(3)	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 | CDO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,468	2,346	2,332	2,512
Net Realized and Unrealized Gains (Losses) Included in income	(135)	45	(249)	34
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	157	(112)	352	(267)
Gross Transfers In	6	0	63	0
Gross Transfers Out	(54)	0	(56)	0
Other	0	0	0	0
Fair Value End of Period	2,442	2,279	2,442	2,279
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	253	(162)	255
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	6	128	6	51
Net Realized and Unrealized Gains (Losses) Included in income	0	0	0	11
Other Comprehensive Income (Loss)	1	(3)	0	0
Purchases, Sales, Issuances and Settlements, Net	5	(112)	6	(123)
Gross Transfers In	0	1	0	76
Gross Transfers Out	0	(10)	0	(11)
Other	0	0	0	0
Fair Value End of Period	12	4	12	4
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	1,935	1,897	1,948	1,827
Net Realized and Unrealized Gains (Losses) Included in income	133	114	245	256
Other Comprehensive Income (Loss)	(23)	(1)	(27)	(7)
Purchases, Sales, Issuances and Settlements, Net	(23)	89	(38)	23
Gross Transfers In	0	0	47	0
Gross Transfers Out	(14)	0	(167)	0
Other	0	0	0	0
Fair Value End of Period	2,008	2,099	2,008	2,099
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	174	122	295	245
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	108	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	(1)	0	(7)	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	107	113	107	113
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