Share-Based Compensation Schedule of Share-based Compensation Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Expense [Line Items]
Share-based compensation expense	$ 22.4	$ 35.6	$ 34.7
Stock Options [Member]
Share-based Compensation Expense [Line Items]
Share-based compensation expense	2.3	2.3	2.9
Restricted Share Awards [Member]
Share-based Compensation Expense [Line Items]
Share-based compensation expense	24.6	23.7	25.6
Performance Share Units [Member]
Share-based Compensation Expense [Line Items]
Share-based compensation expense	(4.5)	9.4	6.2
Restricted Share Units (RSUs) [Member]
Share-based Compensation Expense [Line Items]
Share-based compensation expense	$ 0.0	$ 0.2	$ 0.0