Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation, equity classified awards	$ 2.2	$ 2.4	$ 4.6	$ 5.5
Stock-based compensation, liability classified awards	(1.1)	0.6	(0.8)	0.5
Total pre-tax stock-based compensation expense	1.1	3.0	3.8	6.0
Book income tax benefit	(0.4)	(1.1)	(1.4)	(2.3)
Total stock-based compensation expense, net of tax	$ 0.7	$ 1.9	$ 2.4	$ 3.7