Reinsurance - Summary of the Impact of Funds Withheld (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Effects of Reinsurance [Line Items]
Total net investment income	$ 712	$ 1,105
Net realized losses on Fortitude Re funds withheld assets	(135)	(103)
Income (loss) before income tax expense (benefit)	987	960
Income tax benefit	224	262
Net income (loss)	763	698
Change in unrealized appreciation on available for sale securities	(249)	317
Comprehensive income (loss)	35	1,334
Fortitude Re funds withheld assets
Effects of Reinsurance [Line Items]
Total net investment income	23	40
Fortitude Holdings
Effects of Reinsurance [Line Items]
Total net investment income	23	40
Net realized losses on Fortitude Re funds withheld assets	(3)	(43)
Income (loss) before income tax expense (benefit)	20	(3)
Income tax benefit	4	(1)
Net income (loss)	16	(2)
Comprehensive income (loss)	3	(4)
Fortitude Holdings | Fortitude Re funds withheld assets
Effects of Reinsurance [Line Items]
Net realized losses on Fortitude Re funds withheld assets	(13)	(2)
Fortitude Holdings | Fortitude Re funds withheld assets | Embedded derivatives
Effects of Reinsurance [Line Items]
Net realized losses on Fortitude Re funds withheld assets	10	(41)
Fortitude Holdings | Other investments
Effects of Reinsurance [Line Items]
Change in unrealized appreciation on available for sale securities	$ (13)	$ (2)