Claim, Claim Adjustment Expense and Future Policy Benefit Reserves (Specialty - Net Prior Year Claim and Allocated Claim Adjustment Expense Reserve Development) (Details) - Specialty - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 23	$ 35	$ 75
Other Professional Liability and Management Liability	24	(15)	(69)
Surety	(73)	(69)	(92)
Warranty	(14)	(7)	(15)
Other	(5)	(5)	9
Total pretax (favorable) unfavorable development	$ (45)	$ (61)	$ (92)