Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024	Dec. 31, 2023
Derivative liabilities, net
Fair Value Beginning of Year	$ (31)	$ 100	$ (31)	$ 100	$ (104)	$ (28)	$ (94)	$ (479)
Net Realized and Unrealized (Gains) Losses Included in Income	45	158	81	197
Other Comprehensive (Income) Loss	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	28	(1)	(84)	345
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	37	0	37
Fair Value End of Period	(31)	100	(31)	100
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(30)	(151)	(64)	(99)
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
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	Revenues	Revenues
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive income	Other comprehensive income	Other comprehensive income	Other comprehensive income
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)	Realized Investment Gains (Losses)
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	$ 3,733	$ 4,104	$ 3,733	$ 4,104	3,457	3,481	4,281	4,151
Net Realized and Unrealized Gains (Losses) Included in Income	(1)	(12)	23	8
Other Comprehensive Income (Loss)	7	162	72	196
Purchases, Sales, Issuances and Settlements, Net	287	(342)	425	(782)
Gross Transfers In	9	0	108	552
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	(26)	0	(376)	(67)
Other	0	15	0	46
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	3	5	10	(7)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	17	100	51	56
Equity securities
Derivative liabilities, net
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	61	13	61	13	46	15	13	14
Net Realized and Unrealized Gains (Losses) Included in Income	2	1	6	1
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	5	2	23	2
Gross Transfers In	8	0	17	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	0	(1)
Other	0	(3)	0	(3)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0	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	0	0
Other invested assets
Derivative liabilities, net
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value	93	158	93	158	93	163	145	221
Net Realized and Unrealized Gains (Losses) Included in Income	(5)	(3)	(5)	(16)
Other Comprehensive Income (Loss)	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	5	5	(24)	(34)
Gross Transfers In	0	0	1	0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Transfers out of Level 3	0	0	(63)	(13)
Other	0	11	21	0
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	0	(2)	(12)
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
Derivative liabilities, net
Derivative liabilities, net
Fair Value Beginning of Period		(39)		(453)
Net Realized and Unrealized (Gains) Losses Included in Income		1		41
Other Comprehensive (Income) Loss		0		0
Purchases, Sales, Issuances and Settlements, Net		2		376
Gross Transfers In		0		0
Gross Transfers Out		0		0
Other		37		37
Fair Value End of Period		1		1
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period		2		7
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period		0		0
Net Realized and Unrealized (Gains) Losses Included in Income		1		41
Fortitude Re funds withheld payable
Derivative liabilities, net
Fair Value Beginning of Year	(103)	0	(103)	0	(185)	(128)	(154)	(148)
Net Realized and Unrealized (Gains) Losses Included in Income	54	157	109	158
Other Comprehensive (Income) Loss	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	28	(3)	(84)	(10)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	(103)	0	(103)	0
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(30)	(153)	(64)	(106)
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 Liabilities
Derivative liabilities, net
Fair Value Beginning of Year	72	99	72	99	$ 81	$ 100	$ 99	$ 122
Net Realized and Unrealized (Gains) Losses Included in Income	(9)	0	(28)	(2)
Other Comprehensive (Income) Loss	0	0	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0	0	(21)
Gross Transfers In	0	0	0	0
Gross Transfers Out	0	0	0	0
Other	0	0	0	0
Fair Value End of Period	72	99	72	99
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