Claim and Claim Adjustment Expense Reserves (Commercial - Net prior year claim and allocated claim adjustment expense reserve development) (Details) - Commercial - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 0	$ 0	$ 11	$ 21
General Liability	0	0	70	41
Workers' Compensation	(2)	(2)	(100)	(86)
Property and Other	0	0	2	(2)
Total pretax (favorable) unfavorable development	$ (2)	$ (2)	$ (17)	$ (26)