Fair Value Measurements - Changes in level 3 recurring fair value measurements, assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 31,627	$ 31,578
Net Realized and Unrealized Gains (Losses) Included in Income	666	1,332
Other Comprehensive Income (Loss)	(3,929)	(352)
Purchases, Sales, Issuances and Settlements, Net	689	(56)
Gross Transfers In	3,785	1,879
Gross Transfers Out	(4,191)	(2,692)
Other	0	(62)
Fair Value End of Period	28,647	31,627
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	154	661
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ (2,683)	$ 1,163
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	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)
Gross Transfers Out	$ 5
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]	Total net realized gains (losses)	Total net realized gains (losses)
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 26,862	$ 26,889
Net Realized and Unrealized Gains (Losses) Included in Income	612	653
Other Comprehensive Income (Loss)	(3,907)	(339)
Purchases, Sales, Issuances and Settlements, Net	1,704	670
Gross Transfers In	3,311	1,732
Gross Transfers Out	(3,683)	(2,681)
Other	0	(62)
Fair Value End of Period	24,899	26,862
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(2,683)	1,163
Bonds available for sale | Net realized gains/(losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Realized and Unrealized Gains (Losses) Included in Income	(82)	(1)
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	1,431	2,105
Net Realized and Unrealized Gains (Losses) Included in Income	1	15
Other Comprehensive Income (Loss)	(533)	(9)
Purchases, Sales, Issuances and Settlements, Net	(104)	(358)
Gross Transfers In	40	0
Gross Transfers Out	(11)	(260)
Other	0	(62)
Fair Value End of Period	824	1,431
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(223)	254
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	5
Net Realized and Unrealized Gains (Losses) Included in Income	1	0
Other Comprehensive Income (Loss)	3	(1)
Purchases, Sales, Issuances and Settlements, Net	(10)	1
Gross Transfers In	3	5
Gross Transfers Out	(3)	(3)
Other	0	0
Fair Value End of Period	1	7
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(1)	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	2,641	2,349
Net Realized and Unrealized Gains (Losses) Included in Income	37	(20)
Other Comprehensive Income (Loss)	(238)	(31)
Purchases, Sales, Issuances and Settlements, Net	(87)	188
Gross Transfers In	1,155	524
Gross Transfers Out	(661)	(369)
Other	0	0
Fair Value End of Period	2,847	2,641
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(217)	(141)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	10,378	11,694
Net Realized and Unrealized Gains (Losses) Included in Income	452	595
Other Comprehensive Income (Loss)	(1,319)	(127)
Purchases, Sales, Issuances and Settlements, Net	(1,511)	(1,163)
Gross Transfers In	8	8
Gross Transfers Out	(455)	(629)
Other	0	0
Fair Value End of Period	7,553	10,378
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(504)	790
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,190	922
Net Realized and Unrealized Gains (Losses) Included in Income	7	25
Other Comprehensive Income (Loss)	(162)	(49)
Purchases, Sales, Issuances and Settlements, Net	137	414
Gross Transfers In	102	57
Gross Transfers Out	(348)	(179)
Other	0	0
Fair Value End of Period	926	1,190
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(133)	(55)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	11,215	9,814
Net Realized and Unrealized Gains (Losses) Included in Income	114	38
Other Comprehensive Income (Loss)	(1,658)	(122)
Purchases, Sales, Issuances and Settlements, Net	3,279	1,588
Gross Transfers In	2,003	1,138
Gross Transfers Out	(2,205)	(1,241)
Other	0	0
Fair Value End of Period	12,748	11,215
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	(1,605)	315
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,697	2,698
Net Realized and Unrealized Gains (Losses) Included in Income	(283)	27
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(1,009)	(34)
Gross Transfers In	411	6
Gross Transfers Out	(289)	0
Other	0	0
Fair Value End of Period	1,527	2,697
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(200)	41
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 | Net realized gains/(losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Realized and Unrealized Gains (Losses) Included in Income	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	134	0
Net Realized and Unrealized Gains (Losses) Included in Income	(5)	(1)
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	158	135
Gross Transfers In	334	0
Gross Transfers Out	(205)	0
Other	0	0
Fair Value End of Period	416	134
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(2)	(1)
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	196	139
Net Realized and Unrealized Gains (Losses) Included in Income	(39)	3
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	16	54
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	173	196
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(38)	(87)
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 | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	35	47
Net Realized and Unrealized Gains (Losses) Included in Income	(6)	(3)
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(1)	(15)
Gross Transfers In	0	6
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	28	35
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(4)	2
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 | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,332	2,512
Net Realized and Unrealized Gains (Losses) Included in Income	(233)	28
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(1,182)	(208)
Gross Transfers In	77	0
Gross Transfers Out	(84)	0
Other	0	0
Fair Value End of Period	910	2,332
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(156)	127
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	6	51
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	11
Other Comprehensive Income (Loss)	0	1
Purchases, Sales, Issuances and Settlements, Net	27	(123)
Gross Transfers In	16	77
Gross Transfers Out	(9)	(11)
Other	0	0
Fair Value End of Period	39	6
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	3
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Equity securities | Net realized gains/(losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,948	1,827
Net Realized and Unrealized Gains (Losses) Included in Income	338	641
Other Comprehensive Income (Loss)	(22)	(14)
Purchases, Sales, Issuances and Settlements, Net	(26)	(570)
Gross Transfers In	47	64
Gross Transfers Out	(210)	0
Other	0	0
Fair Value End of Period	2,075	1,948
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	355	617
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other invested assets | Net realized gains/(losses)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Net Realized and Unrealized Gains (Losses) Included in Income	(8)	11
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	114	113
Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(7)	1
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	107	114
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	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