Claim and Claim Adjustment Expense Reserves (Specialty - Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development) (Details) - Specialty - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ (8)	$ 5	$ 18
Other Professional Liability and Management Liability	49	37	50
Surety	(68)	(43)	(83)
Warranty	20	(11)	(21)
Other	(2)	(2)	(4)
Total pretax (favorable) unfavorable development	$ (9)	$ (14)	$ (40)