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Schedule II - Valuation and Qualifying Accounts (Tables)
 12 Months Ended
Dec. 31, 2017
Notes Tables  
Summary of Allowance for Doubtful Accounts and Revenue Adjustments [Table Text Block]
Allowance for Doubtful
Accounts
, Revenue
Adjustments and Other for
the Years Ended:
  
Balance at Beginning of
Year
    
Charged to
Expense/
Against
Revenue
    
Write-Offs,
Net of
Recoveries
    
Balance at
End of Year
  
                                 
December 31, 201
5
   $
9.5
     $
9.5
     $
(9.1
 )   $
9.9
  
December 31, 201
6
    
9.9
      
19.5
      
(16.0
 )    
13.4
  
December 31, 201
7
    
13.4
      
29.3
      
(18.7
 )    
24.0