Insurance Liabilities - Net Loss Reserve Discount Benefit (Charge) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Net Loss Reserve Discount Benefit (Charge) [Line Items]
Current accident year	$ 36	$ 20	$ 92	$ 86
Accretion and other adjustments to prior year discount	(34)	(49)	(119)	(217)
Net reserve discount benefit (charge)	2	(29)	(27)	(131)
Change in discount on loss reserves ceded under retroactive reinsurance	7	22	27	100
Net change in total reserve discount	9	(7)	0	(31)
United Kingdom
Net Loss Reserve Discount Benefit (Charge) [Line Items]
Net change in total reserve discount	$ (35)	$ 1	$ (18)	$ 1