Insurance Liabilities - Net Loss Reserve Discount Benefit (Charge) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Net Loss Reserve Discount Benefit (Charge) [Line Items]
Current accident year	$ 23	$ 23
Accretion and other adjustments to prior year discount	25	(40)
Net reserve discount benefit (charge)	48	(17)
Change in discount on loss reserves ceded under retroactive reinsurance	53	1
Net change in total reserve discount	101	(16)
United Kingdom
Net Loss Reserve Discount Benefit (Charge) [Line Items]
Net change in total reserve discount	$ (4)	$ 6