Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS (Narrative) (Details)

v3.8.0.1
FAIR VALUE MEASUREMENTS (Narrative) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2018
Jan. 01, 2018
Dec. 31, 2017
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets $ 93.6 $ 51.0 $ 39.4
Derivative Liability $ 4.4   2.7
Management Estimate of 62% Fe 62.00%    
Impairment Charges, CIP $ 2.6    
Fair Value, Inputs, Level 1 [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets 0.0   0.0
Derivative Liability 0.0   0.0
Fair Value, Inputs, Level 2 [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets 0.0   0.0
Derivative Liability 0.2   0.3
Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets 93.6   39.4
Derivative Liability 4.2   2.4
Not Designated as Hedging Instrument [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets 93.6   39.4
Derivative Liability 4.2   2.4
Derivative Financial Instruments, Assets [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets 91.2   37.9
Derivative Financial Instruments, Assets [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative assets 2.4   1.5
Other Current Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Fair Value, Inputs, Level 3 [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative Liability 0.0   0.0
Other Current Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member]      
Fair Value, Assets And Liabilities Components [Line Items]      
Derivative Liability $ 4.2   $ 2.4