Stockholders' Equity (Changes To Equity) (Details) - shares		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Increase (Decrease) in Common Shares Outstanding [Roll Forward]
Common shares outstanding at January 1		177,345,266	180,234,388	196,086,090
Issuance of restricted stock, excluding restricted stock with performance feature		55,626	870,378	447,534
Vesting of performance units		138,374	76,404	136,896
Vesting of restricted stock with performance feature		350,063	40,294	43,774
Forfeitures of restricted stock		(139,634)	(16,795)	(51,332)
Purchase of treasury stock	[1]	(342,073)	(3,859,403)	(16,428,574)
Common shares outstanding at December 31		177,407,622	177,345,266	180,234,388
Shares withheld for the payment of taxes		342,073	147,922	151,967

[1] Includes 342,073, 147,922 and 151,967 shares, respectively, withheld under the terms of stock-based compensation agreements to provide funds for the payment of payroll and income taxes due at the vesting of share-based awards, as well as other stock repurchases under separate authority from our Board of Directors.