Share-Based Compensation Share-based compensation expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Share-based Compensation Expense [Line Items]
Share-based Compensation	$ 12.2	$ 1.7	$ 23.4	$ 7.7
Stock Options [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	0.2	0.6	0.7	1.2
Restricted Share Awards [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	6.8	6.0	15.6	13.3
Performance Share Units [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	5.1	(4.9)	7.0	(6.8)
Restricted Share Units (RSUs) [Member]
Share-based Compensation Expense [Line Items]
Share-based Compensation	$ 0.1	$ 0.0	$ 0.1	$ 0.0