Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Assets (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 30,769	$ 28,647
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	78	55
Other Comprehensive Income (Loss)	286	309
Purchases, Sales, Issuances and Settlements, Net	1,303	642
Gross Transfers In	1,166	382
Gross Transfers Out	(428)	(769)
Other	(26)	60
Fair Value End of Period	33,148	29,326
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(74)	(27)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 244	$ 191
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	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 (loss) income	Other comprehensive (loss) income
Market risk benefit assets, at fair value	$ 1,172		$ 912
Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	1,172		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	$ 1,172	$ 830	$ 912
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 losses	Total net realized losses
Bonds available for sale
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	$ 26,844	$ 24,899
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	142	66
Other Comprehensive Income (Loss)	294	304
Purchases, Sales, Issuances and Settlements, Net	1,471	643
Gross Transfers In	1,163	373
Gross Transfers Out	(368)	(571)
Other	0	8
Fair Value End of Period	29,546	25,722
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	244	191
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	847	824
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	1
Other Comprehensive Income (Loss)	(14)	55
Purchases, Sales, Issuances and Settlements, Net	0	(7)
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	833	873
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	(16)	44
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	1
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0
Gross Transfers In	0	7
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	7	9
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
Bonds available for sale | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,679	2,847
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	2	(102)
Other Comprehensive Income (Loss)	1	51
Purchases, Sales, Issuances and Settlements, Net	(29)	(201)
Gross Transfers In	342	274
Gross Transfers Out	(38)	(421)
Other	0	(16)
Fair Value End of Period	1,957	2,432
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	(4)	50
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	7,640	7,553
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	90	109
Other Comprehensive Income (Loss)	93	(70)
Purchases, Sales, Issuances and Settlements, Net	329	10
Gross Transfers In	0	0
Gross Transfers Out	(39)	(21)
Other	0	0
Fair Value End of Period	8,113	7,581
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	89	(98)
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	633	926
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(5)	7
Other Comprehensive Income (Loss)	46	(3)
Purchases, Sales, Issuances and Settlements, Net	(103)	1
Gross Transfers In	144	34
Gross Transfers Out	(125)	(27)
Other	0	0
Fair Value End of Period	590	938
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	11	(34)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	16,038	12,748
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	55	50
Other Comprehensive Income (Loss)	168	271
Purchases, Sales, Issuances and Settlements, Net	1,274	840
Gross Transfers In	677	58
Gross Transfers Out	(166)	(102)
Other	0	24
Fair Value End of Period	18,046	13,889
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	164	229
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,556	1,527
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	25	41
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(21)	(89)
Gross Transfers In	3	1
Gross Transfers Out	(2)	(198)
Other	0	52
Fair Value End of Period	1,561	1,334
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	13	23
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 | 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	0
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	1
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	1	1
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
Other bond securities | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	211	416
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	8	1
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	(96)
Gross Transfers In	3	0
Gross Transfers Out	0	(191)
Other	0	0
Fair Value End of Period	222	130
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	8	3
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	158	173
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	3	5
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(1)	(12)
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	160	166
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	2	(3)
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	17	28
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	(1)
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	17	27
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	(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 | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	1,169	910
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	14	36
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(20)	18
Gross Transfers In	0	1
Gross Transfers Out	(2)	(7)
Other	0	52
Fair Value End of Period	1,161	1,010
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	3	24
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	56	39
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	3	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	27
Gross Transfers In	0	8
Gross Transfers Out	(1)	0
Other	0	0
Fair Value End of Period	58	74
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	3	0
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
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	2,070	2,075
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	(92)	(52)
Other Comprehensive Income (Loss)	(8)	5
Purchases, Sales, Issuances and Settlements, Net	(33)	58
Gross Transfers In	0	0
Gross Transfers Out	(57)	0
Other	(26)	0
Fair Value End of Period	1,854	2,086
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(90)	(50)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period	243	107
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income	0	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(114)	3
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	129	110
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