Share-Based Compensation Share-based compensation expense (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Share-based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	$ 5.2	$ 12.2	$ 16.9	$ 23.4
Stock Options [Member]
Share-based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	0.0	0.2	0.3	0.7
Performance Share Units [Member]
Share-based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	0.3	5.1	5.5	7.0
Restricted Shares [Member]
Share-based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	4.8	6.8	10.9	15.6
Restricted Share Units (RSUs) [Member]
Share-based Compensation Expense [Line Items]
Allocated Share-based Compensation Expense	0.1	0.1	0.2	0.1
Net gain (loss) from asset sales [Member]
Share-based Compensation Expense [Line Items]
Accelerated Share Based Compensation	0.0	0.0	1.5	0.0
General and Administrative Expense [Member]
Share-based Compensation Expense [Line Items]
Accelerated Share Based Compensation	1.3	1.2	8.2	4.0
Total [Member]
Share-based Compensation Expense [Line Items]
Accelerated Share Based Compensation	$ 1.3	$ 1.2	$ 9.7	$ 4.0