Fair Value Measurements - Net Realized and Unrealized Gains and Losses Included in Income Related to Level 3 Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2025	Jun. 30, 2024
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	$ 20	$ 21	$ 24	$ 20
Net realized gains (losses), liabilities	$ (5)	$ 8	$ 36	$ 39
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Revenues	Revenues	Revenues	Revenues
Derivative liabilities, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities		$ (12)		$ 40
Fortitude Re funds withheld payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities	$ 14	(8)	$ 55	1
Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities	(19)	28	(19)	(2)
Bonds available for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	15	23	14	32
Other bond securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	2	2	6	1
Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	3	0	4	0
Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	$ 0	$ (4)	$ 0	$ (13)
Net Investment Income
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Net Investment Income	Net Investment Income	Net Investment Income	Net Investment Income
Net Investment Income | Derivative liabilities, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities		$ 0		$ 0
Net Investment Income | Fortitude Re funds withheld payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities	$ 0	0	$ 0	0
Net Investment Income | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities	0	0	0	0
Net Investment Income | Bonds available for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	5	25	13	40
Net Investment Income | Other bond securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	2	2	6	1
Net Investment Income | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	3		4
Net Investment Income | Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets		(4)		(13)
Net Realized Gains (Losses) | Derivative liabilities, net
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities		(12)		40
Net Realized Gains (Losses) | Fortitude Re funds withheld payable
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities	14	(8)	55	1
Net Realized Gains (Losses) | Other Liabilities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), liabilities	(19)	28	(19)	(2)
Net Realized Gains (Losses) | Bonds available for sale
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	10	(2)	1	(8)
Net Realized Gains (Losses) | Other bond securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	0	0	0	0
Net Realized Gains (Losses) | Equity securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets	$ 0		$ 0
Net Realized Gains (Losses) | Other invested assets
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net realized gains (losses), assets		$ 0		$ 0