Annual report pursuant to Section 13 and 15(d)

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

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DERIVATIVE INSTRUMENTS AND HEDGING ACTIVITIES (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - Not Designated as Hedging Instrument [Member] - USD ($)
$ in Millions
Dec. 31, 2016
Dec. 31, 2015
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value $ 33.1 $ 7.8
Derivative liability, fair value 0.5 4.0
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 1.5 0.0
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 0.6
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 21.3 5.8
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 10.3 2.0
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 $ 0.5 $ 3.4