Fair Value Measurements - Changes in level 3 recurring fair value measurements, assets (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2023	Dec. 31, 2022	Jan. 01, 2021	Dec. 31, 2020
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			$ 28,647	$ 31,627
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			440	666
Other Comprehensive Income (Loss)			474	(3,929)
Purchases, Sales, Issuances and Settlements, Net			1,508	689
Gross Transfers In			1,819	3,785
Gross Transfers Out			(2,342)	(4,191)
Other			223	0
Fair Value End of Period	$ 30,769	$ 28,647	30,769	28,647
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			(206)	154
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period			$ 98	$ (2,683)
Fair Value, Asset, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	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 loss	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss
Gross Transfers Out			$ 0
Market risk benefit assets, at fair value	$ 912	$ 796	$ 912	$ 796	$ 338	$ 338
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss	Other comprehensive loss
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues		Revenues
Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	$ 912	$ 796	$ 912	$ 796
Level 3 | Recurring Basis
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Market risk benefit assets, at fair value	$ 912	$ 796	$ 912	$ 796
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)	Total net realized gains (losses)	Total net realized gains (losses)
Fair Value, Liability, 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)	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			$ 24,899	$ 26,862
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			530	612
Other Comprehensive Income (Loss)			463	(3,907)
Purchases, Sales, Issuances and Settlements, Net			1,132	1,704
Gross Transfers In			1,760	3,311
Gross Transfers Out			(2,084)	(3,683)
Other			144	0
Fair Value End of Period	$ 26,844	$ 24,899	26,844	24,899
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			98	(2,683)
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			824	1,431
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			(2)	1
Other Comprehensive Income (Loss)			67	(533)
Purchases, Sales, Issuances and Settlements, Net			(31)	(104)
Gross Transfers In			0	40
Gross Transfers Out			(11)	(11)
Other			0	0
Fair Value End of Period	847	824	847	824
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			35	(223)
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			1	7
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			1	1
Other Comprehensive Income (Loss)			1	3
Purchases, Sales, Issuances and Settlements, Net			(5)	(10)
Gross Transfers In			11	3
Gross Transfers Out			(2)	(3)
Other			0	0
Fair Value End of Period	7	1	7	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			1	(1)
Bonds available for sale | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			2,847	2,641
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			(104)	37
Other Comprehensive Income (Loss)			24	(238)
Purchases, Sales, Issuances and Settlements, Net			(595)	(87)
Gross Transfers In			818	1,155
Gross Transfers Out			(1,295)	(661)
Other			(16)	0
Fair Value End of Period	1,679	2,847	1,679	2,847
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			(24)	(217)
Bonds available for sale | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			7,553	10,378
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			430	452
Other Comprehensive Income (Loss)			12	(1,319)
Purchases, Sales, Issuances and Settlements, Net			(249)	(1,511)
Gross Transfers In			33	8
Gross Transfers Out			(139)	(455)
Other			0	0
Fair Value End of Period	7,640	7,553	7,640	7,553
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			(63)	(504)
Bonds available for sale | CMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			926	1,190
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			(23)	7
Other Comprehensive Income (Loss)			(49)	(162)
Purchases, Sales, Issuances and Settlements, Net			(58)	137
Gross Transfers In			223	102
Gross Transfers Out			(386)	(348)
Other			0	0
Fair Value End of Period	633	926	633	926
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			(94)	(133)
Bonds available for sale | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			12,748	11,215
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			228	114
Other Comprehensive Income (Loss)			408	(1,658)
Purchases, Sales, Issuances and Settlements, Net			2,070	3,279
Gross Transfers In			675	2,003
Gross Transfers Out			(251)	(2,205)
Other			160	0
Fair Value End of Period	16,038	12,748	16,038	12,748
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			243	(1,605)
Other bond securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			1,527	2,697
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			59	(283)
Other Comprehensive Income (Loss)			0	0
Purchases, Sales, Issuances and Settlements, Net			123	(1,009)
Gross Transfers In			5	411
Gross Transfers Out			(238)	(289)
Other			80	0
Fair Value End of Period	1,556	1,527	1,556	1,527
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			(56)	(200)
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			0
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			0
Other Comprehensive Income (Loss)			0
Purchases, Sales, Issuances and Settlements, Net			1
Gross Transfers In			0
Gross Transfers Out			0
Other			0
Fair Value End of Period	1	0	1	0
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period			0
Other bond securities | Corporate debt
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			416	134
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			(14)	(5)
Other Comprehensive Income (Loss)			0	0
Purchases, Sales, Issuances and Settlements, Net			0	158
Gross Transfers In			0	334
Gross Transfers Out			(191)	(205)
Other			0	0
Fair Value End of Period	211	416	211	416
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			(15)	(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 | RMBS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			173	196
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			9	(39)
Other Comprehensive Income (Loss)			0	0
Purchases, Sales, Issuances and Settlements, Net			(24)	16
Gross Transfers In			0	0
Gross Transfers Out			0	0
Other			0	0
Fair Value End of Period	158	173	158	173
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			(5)	(38)
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			28	35
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			(4)	(6)
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	17	28	17	28
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			0	(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 | CLO/ABS
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			910	2,332
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			68	(233)
Other Comprehensive Income (Loss)			0	0
Purchases, Sales, Issuances and Settlements, Net			153	(1,182)
Gross Transfers In			5	77
Gross Transfers Out			(47)	(84)
Other			80	0
Fair Value End of Period	1,169	910	1,169	910
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			(36)	(156)
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			39	6
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			1	(1)
Other Comprehensive Income (Loss)			0	0
Purchases, Sales, Issuances and Settlements, Net			27	27
Gross Transfers In			10	16
Gross Transfers Out			(20)	(9)
Other			(1)	0
Fair Value End of Period	56	39	56	39
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			1	(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 invested assets
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair Value Beginning of Period			2,075	1,948
MRBs and Net Realized and Unrealized Gains (Losses) Included in Income			(150)	338
Other Comprehensive Income (Loss)			11	(22)
Purchases, Sales, Issuances and Settlements, Net			90	(26)
Gross Transfers In			44	47
Gross Transfers Out			0	(210)
Other			0	0
Fair Value End of Period	2,070	2,075	2,070	2,075
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period			(151)	355
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			107	114
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			136	(7)
Gross Transfers In			0	0
Gross Transfers Out			0	0
Other			0	0
Fair Value End of Period	$ 243	$ 107	243	107
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