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Cash, Cash Equivalents and Restricted Cash (Schedule of Restricted Cash) (Details) - USD ($)
$ in Millions
Jun. 30, 2019
Dec. 31, 2018
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted cash included in other current assets $ 18.0 $ 30.3
Restricted cash included in other long-term assets 5.7 6.3
Other financial assurance [Member]    
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted cash included in other current assets 0.5 0.2
Restricted cash included in other long-term assets 0.3 0.3
ARO financial assurance [Member]    
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted cash included in other current assets 16.9 16.6
Workers compensation financial assurance [Member]    
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted cash included in other current assets 0.6  
Restricted cash included in other long-term assets 5.4 6.0
Lease turnover financial assurance [Member]    
Restricted Cash and Cash Equivalents Items [Line Items]    
Restricted cash included in other current assets $ 0.0 13.5
Restricted cash included in other long-term assets   $ 0.0