Share-Based Compensation and Equity - Share-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	$ 24.0	$ 36.6	$ 33.9
Tax benefit	(5.6)	(8.2)	(8.3)
Total share-based compensation, net of tax	18.4	28.4	25.6
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	1.5	2.8	4.6
Tax benefit	(0.2)	(0.6)	(1.3)
Total share-based compensation, net of tax	1.3	2.2	3.3
Restricted Stock Units [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	11.6	19.8	16.4
Tax benefit	(2.5)	(4.3)	(4.0)
Total share-based compensation, net of tax	9.1	15.5	12.4
Performance Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	10.9	14.0	12.9
Tax benefit	(2.9)	(3.3)	(3.0)
Total share-based compensation, net of tax	$ 8.0	$ 10.7	$ 9.9