Share-Based Compensation and Equity - Share-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	$ 33.9	$ 22.2	$ 12.4
Tax benefit	(8.3)	(7.0)	(3.8)
Stock option expense, net of tax	25.6	15.2	8.6
Stock Options [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	4.6	2.7	3.6
Tax benefit	(1.3)	(0.9)	(1.3)
Stock option expense, net of tax	3.3	1.8	2.3
Restricted Stock Units [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	16.4	10.7	8.6
Tax benefit	(4.0)	(3.1)	(2.4)
Stock option expense, net of tax	12.4	7.6	6.2
Performance Shares [Member]
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Pre-tax compensation expense	12.9	8.8	0.2
Tax benefit	(3.0)	(3.0)	(0.1)
Stock option expense, net of tax	$ 9.9	$ 5.8	$ 0.1