Annual report pursuant to Section 13 and 15(d)

SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION (Deferred Revenue) (Details)

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SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION SUPPLEMENTARY FINANCIAL STATEMENT INFORMATION (Deferred Revenue) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Jan. 01, 2018
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]      
Contract with Customer, Liability, Revenue Recognized $ 38.5 $ 51.3  
Other Current Liabilities [Member]      
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]      
Contract with Customer, Liability, Current 22.1 21.0 $ 23.8
Contract With Customer, Liability, Period Increase (Decrease) 1.1 (2.8)  
Contract with Customer, Liability 12.8 12.8  
Other Noncurrent Liabilities [Member]      
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]      
Deferred Revenue (Long-Term) 25.7 38.5 $ 51.4
Contract With Customer, Liability, Period Increase (Decrease) (12.8) (12.9)  
Take or Pay Contracts [Member] | Other Current Liabilities [Member]      
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]      
Contract with Customer, Liability $ 9.3 $ 8.2