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Revenues - Textuals (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Mar. 31, 2020
Dec. 31, 2018
Disaggregation of Revenue [Line Items]        
Interest Income $ 2.7 $ 2.1    
Accounts Receivable [Member]        
Disaggregation of Revenue [Line Items]        
Allowance for Doubtful Accounts Receivable 0.1     $ 0.1
Provision for Doubtful Accounts 0.0 $ 0.2    
Miscellaneous Receivables [Member]        
Disaggregation of Revenue [Line Items]        
Allowance for Doubtful Accounts Receivable 4.3     4.3
Long-term Customer Receivables        
Disaggregation of Revenue [Line Items]        
Long-term Investments and Receivables, Net $ 11.3     $ 11.1
Scenario, Forecast | One year or longer        
Disaggregation of Revenue [Line Items]        
Deferred Revenue     $ 5,000.0  
Deferred Revenue, Percentage of Total, Expected to be Recognized in Next Twelve Months     47.00%  
Deferred Revenue, Percentage of Total, Expected to be Recognized Beyond Twelve Months     53.00%