Stock-Based Compensation (Allocation of Share-based Compensation Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition	1 year 7 months
Stock compensation expense	$ 16.1	$ 19.5	$ 19.2
Stock Option and Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	7.8	8.6	9.2
Performance-Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	4.1	6.7	6.0
Performance-Vesting Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0.1	0.1	0.7
Performance-vesting Shares or Units Dividend Equivalents [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0.1	0.2	0.2
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0.8	0.7	0.6
Deferred Compensation Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	$ 3.2	$ 3.2	$ 2.5