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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 0	$ 1	$ 9	$ 9
Other Professional Liability and Management Liability	(1)	13	(1)	13
Surety	(7)	(19)	(7)	(28)
Warranty	0	0	(9)	(9)
Other	4	(5)	4	(5)
Total pretax (favorable) unfavorable development	$ (4)	$ (10)	$ (4)	$ (20)