Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Deferred Tax Assets:
Property and casualty claim and claim adjustment expense reserves	$ 188	$ 173
Unearned premium reserves	190	193
Deferred Revenue	64	64
Employee benefits	35	46
Deferred retroactive reinsurance benefit	89	90
Net unrealized losses	706
Other assets	116	88
Gross deferred tax assets	1,388	654
Deferred Tax Liabilities:
Investment valuation differences	59	93
Deferred acquisition costs	113	99
Net unrealized gains		272
Software and hardware	21	27
Other liabilities	17	21
Gross deferred tax liabilities	210	512
Net deferred tax asset	$ 1,178	$ 142