Reinsurance - Summary of the Composition of Pool of Assets (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Effects of Reinsurance [Line Items]
Fixed maturity securities - available for sale	$ 71,184	$ 64,006
Fixed maturity securities - fair value option	743	745
Short-term investments	9,417	14,462
Other	4,602	4,735
Total assets	163,415	161,322
Carrying Value
Effects of Reinsurance [Line Items]
Short-term investments	4,557	4,673
Other	2	15
Commercial mortgage loans
Effects of Reinsurance [Line Items]
Loans, carrying value	2,869	3,305
Fortitude Holdings
Effects of Reinsurance [Line Items]
Change in net unrealized gains (losses), gross	58	(35)
Change in net unrealized gains (losses), net of tax	46	(28)
Derivative asset, Fair value of collateral	1	9
Derivative liability, Fair value of collateral	31	2
Fortitude Holdings | Carrying Value
Effects of Reinsurance [Line Items]
Fixed maturity securities - available for sale	1,787	1,918
Fixed maturity securities - fair value option	736	721
Short-term investments	19	15
Funds withheld investment assets	2,972	3,104
Derivative assets, net	0	1
Other	133	115
Total assets	3,105	3,220
Fortitude Holdings | Estimated Fair Value
Effects of Reinsurance [Line Items]
Fixed maturity securities - available for sale	1,787	1,918
Fixed maturity securities - fair value option	736	721
Short-term investments	19	15
Funds withheld investment assets	2,961	3,091
Derivative assets, net	0	1
Other, fair value	133	115
Total	3,094	3,207
Fortitude Holdings | Commercial mortgage loans | Carrying Value
Effects of Reinsurance [Line Items]
Loans, carrying value	430	450
Fortitude Holdings | Commercial mortgage loans | Estimated Fair Value
Effects of Reinsurance [Line Items]
Loans, fair value	$ 419	$ 437