Share-Based Compensation Share-based compensation expense (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Expense [Line Items]
Share-based Compensation	$ 11.2	$ 6.0
Stock Options [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	0.5	0.6
Restricted Share Awards [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	8.8	7.3
Performance Share Units [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	1.9	(1.9)
Restricted Share Units (RSUs) [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	$ 0.0	$ 0.0