Stock-Based Compensation (Share-based Compensation Expense) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (income)	$ (1.2)	$ 4.1	$ 6.0	$ 11.9
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (income)	0.5	0.6	1.5	1.8
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (income)	0.8	0.8	3.7	3.5
Performance stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (income)	$ (2.5)	$ 2.7	$ 0.8	$ 6.6