Income Taxes (Significant components of the Company's deferred tax assets and liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred Tax Assets:
Property and casualty claim and claim adjustment expense reserves	$ 173	$ 157
Unearned premium reserves	193	174
Deferred Revenue	64	62
Employee benefits	46	122
Deferred retroactive reinsurance benefit	90	83
Other assets	88	92
Gross deferred tax assets	654	690
Deferred Tax Liabilities:
Investment valuation differences	93	28
Deferred acquisition costs	99	93
Net unrealized gains	272	453
Software and hardware	27	31
Other liabilities	21	19
Gross deferred tax liabilities	512	624
Net deferred tax asset	$ 142	$ 66