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