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, 2022	Mar. 31, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 8	$ 8
Other Professional Liability and Management Liability	0	0
Surety	(9)	(15)
Warranty	(9)	(8)
Other	0	0
Total pretax (favorable) unfavorable development	$ (10)	$ (15)