Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details)

v3.7.0.1
DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - Not Designated as Hedging Instrument [Member] - USD ($)
$ in Millions
Mar. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value $ 59.4 $ 33.1
Derivative liability, fair value 9.1 0.5
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 35.9 21.3
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Customer Supply Agreement [Member] | Derivative Financial Instruments, Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 0.0 0.0
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 23.5 10.3
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 9.1 0.5
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0.0 1.5
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value $ 0.0 $ 0.0