Reinsurance - Summary of the Impact of Funds Withheld (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Effects of Reinsurance [Line Items]
Total net investment income	$ 772	$ 973	$ 3,343	$ 2,942
Net realized losses on Fortitude Re funds withheld assets	(490)	(167)	(851)	(434)
Loss from continuing operations before income tax benefit	714	649	3,218	2,324
Income tax benefit	190	168	852	571
Net loss	524	457	2,366	(1,827)
Change in unrealized appreciation on available for sale securities			537	4
Comprehensive loss	1,026	2,304	4,420	5,657
Fortitude Re funds withheld assets
Effects of Reinsurance [Line Items]
Total net investment income	29	51	108	123
Fortitude Holdings
Effects of Reinsurance [Line Items]
Total net investment income	29	51	108	123
Net realized losses on Fortitude Re funds withheld assets	(59)	(175)	(168)	(196)
Loss from continuing operations before income tax benefit	(30)	(124)	(60)	(73)
Income tax benefit	(7)	(26)	(13)	(15)
Net loss	(23)	(98)	(47)	(58)
Comprehensive loss	0	(31)	(1)	(33)
Fortitude Holdings | Fortitude Re funds withheld assets
Effects of Reinsurance [Line Items]
Net realized losses on Fortitude Re funds withheld assets	(5)	(18)	(59)	(38)
Fortitude Holdings | Fortitude Re funds withheld assets | Embedded derivatives
Effects of Reinsurance [Line Items]
Net realized losses on Fortitude Re funds withheld assets	(54)	(157)	(109)	(158)
Fortitude Holdings | Other investments
Effects of Reinsurance [Line Items]
Change in unrealized appreciation on available for sale securities	$ 23	$ 67	$ 46	$ 25