Stockholders' Equity (Summary Of Shares Repurchased) (Details)	12 Months Ended
	Dec. 31, 2017 item shares	Dec. 31, 2016 shares	Dec. 31, 2015 USD ($) shares
Stockholders' Equity and Common Stock Issued and Outstanding [Abstract]
Purchase of Treasury Stock | $			$ 250,000,000
Shares repurchased | shares	0	0	5,967,313
Number of open share buyback programs | item	0