Equity (Details) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended		3 Months Ended		9 Months Ended		261 Months Ended
	Oct. 20, 2015	Oct. 31, 2015	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Oct. 30, 2015	Dec. 31, 2014
Equity
Preferred stock, par value (in dollars per share)			$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001	$ 0.001		$ 0.001
Common stock, par value (in dollars per share)			$ 0.001	0.001	0.001	0.001	0.001	$ 0.001		$ 0.001
Common stock dividend quarterly declared and paid per share (in dollars per share)				$ 0.40	$ 0.35	$ 1.20	$ 1.05
Share Repurchase Plan
Number of shares repurchased under stock repurchase plan		241,511		2,514,654		5,953,054		22,100,000
Average costs per share				$ 56.60		$ 57.50		$ 30.93
Value of shares repurchased				$ 142.3		$ 342.3
Common Stock and Additional Paid-In (in Shares)
Stock-based compensation ( in shares)						271,438
Stock options exercised (in shares)				9,512		218,524
Repurchase of common shares (in shares)		(241,511)		(2,514,654)		(5,953,054)		(22,100,000)
Total ( in shares)				(2,505,142)		(5,463,092)
Common Stock and Additional Paid-In (in Amount)
Stock-based compensation				$ 5.2		$ 17.6
Stock options exercised				0.4		11.0
Value of shares repurchased				(142.3)		(342.3)
Total				$ (136.7)		$ (313.7)
Weighted Average Exercise/(Purchase) Price
Stock options exercised (in dollars per share)				$ 42.87		$ 52.00
Weighted Average Grant Date Fair Value
Dividends paid				$ 29.3	$ 27.3	$ 89.7	$ 81.7
Subsequent event
Share Repurchase Plan
Increase in authorized number of shares to be repurchased	7,500,000
Remaining number of common stock authorized for repurchase under stock repurchase program (in shares)									8,400,000
Weighted Average Grant Date Fair Value
Common stock quarterly dividend per share (in dollars per share)	$ 0.40
Pending settlement
Share Repurchase Plan
Number of shares repurchased under stock repurchase plan			526,800
Value of shares repurchased			$ 28.4
Common Stock and Additional Paid-In (in Shares)
Repurchase of common shares (in shares)			(526,800)
Common Stock and Additional Paid-In (in Amount)
Value of shares repurchased			$ (28.4)
Restricted stock
Changes in unvested restricted stock grants and RSUs
Granted (in shares)						12,719
RSU's
Changes in unvested restricted stock grants and RSUs
Granted (in shares)						557,760
Weighted Average Grant Date Fair Value
Dividend equivalents						$ 1.0
Performance targets Period						3 years
RSU's | Performance-based
Changes in unvested restricted stock grants and RSUs
Granted (in shares)						225,450
Unvested RSUs and Restricted Stock
Changes in unvested restricted stock grants and RSUs
Unvested at the beginning of the period (in shares)		1,212,490				846,760
Granted (in shares)						570,479
Vested (in shares)						(105,119)
Canceled (in shares)						(99,630)
Unvested at the end of the period (in shares)			1,212,490	1,212,490		1,212,490		1,212,490
Shares reserved for future grants (all plans)						2,096,472
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)		$ 63.90				$ 65.10
Granted (in dollars per shares)						59.42
Vested (in dollars per shares)						59.46
Canceled (in dollars per shares)						58.56
Unvested at the end of the period (in dollars per shares)			$ 63.90	$ 63.90		$ 63.90		$ 63.90