Claim and Claim Adjustment Expense Reserves and Future Policy Benefit Reserves (Specialty - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - Specialty - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 8	$ 8	$ 17	$ 16
Other Professional Liability and Management Liability	9	0	22	10
Surety	(20)	(15)	(48)	(53)
Warranty	(13)	(6)	(22)	(14)
Other	1	(2)	(4)	1
Total pretax (favorable) unfavorable development	$ (15)	$ (15)	$ (35)	$ (40)