Quarterly report pursuant to Section 13 or 15(d)

FAIR VALUE MEASUREMENTS (Narrative) (Details)

v3.19.1
FAIR VALUE MEASUREMENTS (Narrative) (Details) - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative assets $ 107.4 $ 91.5
Derivative liability 10.5 3.7
Derivative Asset 107.4 91.5
Derivative Liability 10.5 3.7
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 0.7 0.1
Derivative Liability 0.7 3.7
Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative assets 106.7 91.4
Derivative Liability   0.0
Not Designated as Hedging Instrument [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative liability 9.8 0.0
Derivative Asset 106.7 91.4
Other Current Liabilities [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative liability 9.8  
Derivative Liability 9.8  
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Customer Supply Agreement [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative Asset 106.4 89.3
Other Current Assets [Member] | Not Designated as Hedging Instrument [Member] | Valuation, Market Approach [Member] | Provisional Pricing Arrangements [Member] | Fair Value, Inputs, Level 3 [Member]    
Fair Value, Assets And Liabilities Components [Line Items]    
Derivative liability   0.0
Derivative Asset $ 0.3 $ 2.1