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	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Liability for Claims and Claims Adjustment Expense [Line Items]
Medical Professional Liability	$ 18	$ 23	$ 35
Other Professional Liability and Management Liability	50	24	(15)
Surety	(83)	(73)	(69)
Warranty	(21)	(14)	(7)
Other	(4)	(5)	(5)
Total pretax (favorable) unfavorable development	$ (40)	$ (45)	$ (61)