Insurance Liabilities - Net Loss Reserve Discount Benefit (Charge) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024
Net Loss Reserve Discount Benefit (Charge) [Line Items]
Current accident year	$ 23	$ 30
Accretion and other adjustments to prior year discount	(40)	(106)
Net reserve discount benefit (charge)	(17)	(76)
Change in discount on loss reserves ceded under retroactive reinsurance	1	55
Net change in total reserve discount	(16)	(21)
United Kingdom
Net Loss Reserve Discount Benefit (Charge) [Line Items]
Net change in total reserve discount	$ 6	$ (2)