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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 1	$ 0	$ 9	$ 8
Other Professional Liability and Management Liability	13	10	13	10
Surety	(19)	(23)	(28)	(38)
Warranty	0	0	(9)	(8)
Other	(5)	3	(5)	3
Total pretax (favorable) unfavorable development	$ (10)	$ (10)	$ (20)	$ (25)