Stock-Based Compensation (Allocation of Share-based Compensation Costs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average period for recognition	1 year 7 months 6 days
Stock compensation expense	$ 24.4	$ 15.1	$ 16.1
Stock Option and Appreciation Rights [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	9.1	8.6	7.8
Performance-Vesting Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	9.5	2.5	4.1
Cash-settled PSU awards [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0.1	0.0	0.1
Performance-vesting Shares or Units Dividend Equivalents [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0.2	0.1	0.1
Employee Stock Purchase Plan (ESPP) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	0.9	0.9	0.8
Deferred Compensation Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock compensation expense	$ 4.6	$ 3.0	$ 3.2