Earnings Per Share Computations (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Numerator
Net income	$ 50.9	$ 65.6	$ 107.1	$ 120.0
Denominator
Basic weighted-average common shares outstanding	94.7	96.9	94.8	97.3
Dilutive shares	1.0	1.2	1.0	1.1
Weighted-average common and common equivalent shares outstanding - diluted	95.7	98.1	95.8	98.4
Per common share income
Net income, per basic share	$ 0.54	$ 0.68	$ 1.13	$ 1.23
Net income, per diluted share	$ 0.53	$ 0.67	$ 1.12	$ 1.22
Antidilutive stock options and stock awards	0.0	0.0	0.0	0.0