Claim and Claim Adjustment Expense Reserves (Specialty - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - Specialty - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 0	$ 9
Other Professional Liability and Management Liability	0	0
Surety	(18)	0
Warranty	13	(9)
Other	0	0
Total pretax (favorable) unfavorable development	$ (5)	$ 0