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, 2018
Dec. 31, 2017
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value $ 91.5 $ 37.9
Derivative liability, fair value 3.7 2.0
Not Designated as Hedging Instrument [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 91.4 37.9
Derivative liability, fair value 0.0 1.7
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Assets [Member]    
Derivatives, Fair Value [Line Items]    
Derivative asset, fair value 0.1 0.0
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]    
Derivatives, Fair Value [Line Items]    
Derivative liability, fair value 3.7 0.3
Valuation, Market Approach [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 89.3 37.9
Valuation, Market Approach [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 2.1 0.0
Valuation, Market Approach [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 $ 0.0 $ 1.7