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, 2025	Dec. 31, 2024	Dec. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 0	$ (8)	$ 5
Other Professional Liability and Management Liability	69	49	37
Surety	(50)	(68)	(43)
Warranty	10	20	(11)
Other	8	(2)	(2)
Total pretax (favorable) unfavorable development	$ 37	$ (9)	$ (14)