Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Liabilities (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Dec. 31, 2023
Derivative liabilities, net:
Fair Value Beginning of Year	$ 21	$ (210)	$ (28)	$ (479)
Net Realized and Unrealized (Gains) Losses Included in Income	41	31
Other Comprehensive (Income) Loss	0	0
Purchases, Sales, Issuances and Settlements, Net	8	238
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	21	(210)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(2)	25
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 0	$ 0
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	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
Net realized gains/(losses)
Derivative liabilities, net:
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)
Derivative liabilities, net
Derivative liabilities, net:
Fair Value Beginning of Year		$ (453)
Net Realized and Unrealized (Gains) Losses Included in Income		52
Other Comprehensive (Income) Loss		0
Purchases, Sales, Issuances and Settlements, Net		218
Gross Transfers In		0
Gross Transfers Out		0
Other		0
Fair Value End of Period		(183)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period		11
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period		0
Net Realized and Unrealized (Gains) Losses Included in Income		52
Fortitude Re funds withheld payable
Derivative liabilities, net:
Fair Value Beginning of Year	$ (79)	(119)	(128)	(148)
Net Realized and Unrealized (Gains) Losses Included in Income	41	9
Other Comprehensive (Income) Loss	0	0
Purchases, Sales, Issuances and Settlements, Net	8	20
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	(79)	(119)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(2)	14
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other Liabilities
Derivative liabilities, net:
Fair Value Beginning of Year	100	92	$ 100	$ 122
Net Realized and Unrealized (Gains) Losses Included in Income	0	(30)
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	100	92
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