Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS (Narrative) (Details)

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FAIR VALUE MEASUREMENTS (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2017
Dec. 31, 2016
Fair Value, Assets And Liabilities Components [Line Items]    
Loans to and accounts receivable from the Canadian Entities $ 49.0 $ 48.6
Cash equivalents $ 135.0 177.0
Management Estimate of 62% Fe 62.00%  
Contingent Liabilities recognized in Consolidated Financials $ 37.5 37.2
Derivative Asset 59.4 33.1
Derivative Liability 9.1 0.5
Fair Value, Inputs, Level 1 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Loans to and accounts receivable from the Canadian Entities 0.0 0.0
Cash equivalents 90.0 177.0
Contingent Liabilities recognized in Consolidated Financials 0.0 0.0
Derivative Asset 0.0 0.0
Derivative Liability 0.0 0.0
Fair Value, Inputs, Level 2 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Loans to and accounts receivable from the Canadian Entities 0.0 0.0
Cash equivalents 45.0 0.0
Contingent Liabilities recognized in Consolidated Financials 0.0 0.0
Derivative Asset 0.0 1.5
Derivative Liability 0.0 0.0
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Loans to and accounts receivable from the Canadian Entities 49.0 48.6
Cash equivalents 0.0 0.0
Contingent Liabilities recognized in Consolidated Financials 37.5 37.2
Derivative Asset 59.4 31.6
Derivative Liability 9.1 0.5
Not Designated as Hedging Instrument [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative asset, fair value 59.4 33.1
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Market Approach Valuation Technique [Member] | Customer Supply Agreement [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative asset, fair value 35.9 21.3
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Market Approach Valuation Technique [Member] | Provisional Pricing Arrangements [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative asset, fair value $ 23.5 $ 10.3