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		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial	$ 11	$ 21	$ 11	$ 21
General Liability	70	41	70	41
Workers' Compensation	(96)	(82)	(98)	(84)
Property and Other	2	(2)	2	(2)
Total pretax (favorable) unfavorable development	$ (13)	$ (22)	$ (15)	$ (24)