Deferred Policy Acquisition Costs (Deferred Policy Acquisition Costs And Asset Reconciliation Including The Amortized Deferred Policy Acquisition Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Deferred Costs [Roll Forward]
Deferred policy acquisition costs asset at January 1	$ 616	$ 578	$ 565
Capitalized deferred policy acquisition costs	889	846	827
Amortized deferred policy acquisition costs	(863)	(829)	(807)
Amortized shadow deferred policy acquisition costs	(5)	21	(7)
Deferred policy acquisition costs asset at December 31	637	616	578
Property Casualty Insurance Segment [Member]
Deferred Costs [Roll Forward]
Deferred policy acquisition costs asset at January 1	388	379	366
Capitalized deferred policy acquisition costs	840	801	783
Amortized deferred policy acquisition costs	(820)	(792)	(770)
Deferred policy acquisition costs asset at December 31	408	388	379
Life Insurance Product Line [Member]
Deferred Costs [Roll Forward]
Deferred policy acquisition costs asset at January 1	228	199	199
Capitalized deferred policy acquisition costs	49	45	44
Amortized deferred policy acquisition costs	(43)	(37)	(37)
Amortized shadow deferred policy acquisition costs	(5)	21	(7)
Deferred policy acquisition costs asset at December 31	$ 229	$ 228	$ 199