Stock-Based Compensation (Components of Stock-Based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Share-based Payment Arrangement [Abstract]
Equity classified awards expense	$ 2.6	$ 1.8	$ 6.7	$ 5.9
Liability classified awards expense (credit)	0.1	1.4	(0.5)	2.4
Total pre-tax stock-based compensation expense	2.7	3.2	6.2	8.3
Book income tax benefit	(0.7)	(0.9)	(1.6)	(2.2)
Total stock-based compensation expense, net of tax	$ 2.0	$ 2.3	$ 4.6	$ 6.1