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) - USD ($)
$ in Millions
Dec. 31, 2017
Dec. 31, 2016
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value $ 39.4 $ 33.1
Derivative liability, fair value 2.7 0.5
Not Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 39.4 33.1
Derivative liability, fair value 2.4 0.5
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 0.0 1.5
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 0.3 0.0
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 37.9 21.3
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 1.5 10.3
Market Approach Valuation Technique [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value $ 2.4 $ 0.5