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, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Liability for Claims and Claims Adjustment Expense [Line Items]
Commercial Auto	$ 21	$ 30	$ 21	$ 30
General Liability	41	0	41	0
Workers' Compensation	(82)	(42)	(84)	(42)
Property and Other	(2)	12	(2)	12
Total pretax (favorable) unfavorable development	$ (22)	$ 0	$ (24)	$ 0