Share-Based Compensation and Equity - Share-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	$ 14.9	$ 24.0	$ 36.6
Tax benefit	(3.7)	(5.6)	(8.2)
Total share-based compensation, net of tax	11.2	18.4	28.4
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	1.7	1.5	2.8
Tax benefit	(0.5)	(0.2)	(0.6)
Total share-based compensation, net of tax	1.2	1.3	2.2
Restricted Stock Units [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	8.9	11.6	19.8
Tax benefit	(2.2)	(2.5)	(4.3)
Total share-based compensation, net of tax	6.7	9.1	15.5
Performance Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	4.3	10.9	14.0
Tax benefit	(1.0)	(2.9)	(3.3)
Total share-based compensation, net of tax	$ 3.3	$ 8.0	$ 10.7