Stockholders' Equity (Details Textuals) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended	12 Months Ended					60 Months Ended
	Jun. 30, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2008	Dec. 31, 2006	Dec. 31, 2017	Dec. 31, 2011
Schedule Of Stock By Class (Textuals) [Abstract]
Common Stock, shares authorized		800.0
Preferred Stock, par value		$ 0.01
Common Stock, par value		$ 0.01
Number of votes entitled for common stock holders		one vote per share
Aggregate principal amount of debentures outstanding		$ 732.5
Liquidation preference of perpetual preferred stock, per share		$ 1,000
Perpetual Preferred Stock annual cumulative dividend rate		3.0875%
DefinedIntervalInYearstoPayDividendsonPerpetualPreferredStock							five
ElectedMembersToServeOnCompanysBoardOfDirectors		two
Period for payment of dividend on perpetual preferred stock		10
NumberOfFailedAmountOfDividendsOnPreferredStock		six
Authorized amount for common stock repurchase		1,000.0
Treasury Stock, shares		14.0	13.8
Cost of shares repurchased		299.6			199.8	99.8
Amount available for repurchase of shares under share repurchase program		700.4
Maximum amount that can be authorized for repurchase of common stock outside the share repurchase program		100.0
Stock Repurchased During Period, Shares		0	0	4.2
Common stock repurchase	$ 99.9	$ 0	$ 0	$ 99.9
Shares relinquished		0.2	0.1	0.3
Common Stock, shares outstanding		271.7	270.1	268.6				271.1
Common Stock [Member]
Schedule Of Stock By Class (Textuals) [Abstract]
Common Stock, shares authorized		800.0	800.0
Common Stock, par value		$ 0.01	$ 0.01
Common Stock, shares outstanding		271.7	270.1
Preferred Stock [Member]
Schedule Of Stock By Class (Textuals) [Abstract]
Preferred Stock, par value		$ 0.01	$ 0.01
Preferred Stock, shares outstanding		0	0
Preferred Stock, shares authorized		10.0	10.0
Series Common Stock [Member]
Schedule Of Stock By Class (Textuals) [Abstract]
Common Stock, shares authorized		40.0	40.0
Common Stock, par value		$ 0.01	$ 0.01
Common Stock, shares outstanding		0	0
Perpetual Preferred Stock Member
Schedule Of Stock By Class (Textuals) [Abstract]
Preferred Stock, shares outstanding		0	0
Preferred Stock, shares authorized		0.8	0.8
Treasury Stock [Member]
Schedule Of Stock By Class (Textuals) [Abstract]
Treasury Stock, shares		7.7