Stockholders' Equity (Changes To Equity) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Increase (Decrease) in Common Shares Outstanding [Roll Forward]
Common shares outstanding at January 1		180,234,388	196,086,090	198,830,351
Issuance of restricted stock, excluding restricted stock with performance feature		870,378	447,534	376,622
Vesting of performance units		76,404	136,896	416,111
Vesting of restricted stock with performance feature		40,294	43,774	77,430
Forfeitures of restricted stock		(16,795)	(51,332)	(76,107)
Purchase of treasury stock	[1]	(3,859,403)	(16,428,574)	(3,538,317)
Common shares outstanding at December 31		177,345,266	180,234,388	196,086,090
Shares withheld for the payment of taxes		147,922	151,967	279,680
Authorized share repurchase		$ 1,000.0
Stock repurchase program, value		178.8
Value of shares withheld related to tax withholding for share-based compensation		$ 4.7	$ 6.2	$ 11.4

[1] Includes 147,922, 151,967 and 279,680 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.