Equity - Share Repurchases, Dividends, Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions		3 Months Ended		9 Months Ended
	Oct. 24, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Share Repurchase Plan
Number of shares authorized by the Board of Directors to be repurchased under share repurchase plan		8,400,000		8,400,000
Number of shares authorized by the Board of Directors to be repurchased under share repurchase plan, expressed as a percentage of outstanding shares (as a percent)		12.00%		12.00%
Number of shares repurchased under stock repurchase plan				0
Dividends
Common stock quarterly dividend per share (in dollars per share)	$ 0.45
Common stock dividend quarterly declared and paid per share (in dollars per share)		$ 0.45	$ 0.425	$ 1.35	$ 1.225
Dividends paid		$ 32.8	$ 31.5	$ 98.4	$ 88.6
Changes restricted stock grants and RSUs
Unvested at the beginning of the period (in shares)				985,540
Granted (in shares)				446,525
Vested (in shares)				(8,159)
Cancelled (in shares)				(38,274)
Unvested at the end of the period (in shares)		1,385,632		1,385,632
Shares reserved for future grants (all plans)		1,650,458		1,650,458
Weighted Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share)				$ 64.34
Granted (in dollars per shares)				79.60
Vested (in dollars per shares)				62.49
Cancelled (in dollars per shares)				67.84
Unvested at the end of the period (in dollars per shares)		$ 69.18		$ 69.18
Common Stock Including Additional Paid in Capital
Common Stock and Additional Paid-In (in Shares)
Stock-based compensation ( in shares)		2,133		164,435
Stock options exercised (in shares)		9,925		66,455
Total ( in shares)		12,058		230,890
Stock-based compensation expense				$ 23.3
Payments made to tax authorities on employees' behalf				0.8
Common Stock and Additional Paid-In (in Amount)
Stock-based compensation		$ 8.4		22.5
Stock options exercised		0.5		3.4
Total		$ 8.9		$ 25.9
Weighted Average Exercise/(Purchase) Price
Stock options exercised (in dollars per share)		$ 55.73		$ 50.81
RSU's
Dividends
Dividend equivalents				$ 0.9	$ 0.9
Stock-Based Compensation
Vesting period (in years)				3 years
Changes restricted stock grants and RSUs
Granted (in shares)				446,525
RSU's | Performance-based
Changes restricted stock grants and RSUs
Granted (in shares)				169,009