Income Taxes (Components Of Deferred Tax Assets And Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Loss and loss expense reserves	$ 199	$ 191
Unearned premiums	158	151
Investments	5	25
Other	52	42
Total gross deferred tax assets	414	409
Deferred tax liabilities:
Unrealized investment gains, net	907	719
Deferred acquisition costs	195	187
Life policy reserves	162	137
Other	15	4
Total gross deferred tax liabilities	1,279	1,047
Net deferred income tax liability	$ 865	$ 638