Insurance Liabilities - Discounting of Reserves (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Discounting of Reserves [Line Items]
U.S. workers' compensation	$ 2,084	$ 2,111
Retroactive reinsurance	(909)	(936)
Total reserve discount	1,175	1,175
Fortitude RE
Discounting of Reserves [Line Items]
Total reserve discount	$ 725	$ 627
Discount ceded on sale (as a percent)	100.00%	100.00%
United Kingdom
Discounting of Reserves [Line Items]
Total reserve discount	$ 166	$ 184