DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative Asset	$ 107.4	$ 91.5
Derivative liability	10.5	3.7
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	106.7	91.4
Derivative liability	9.8	0.0
Fair Value, Inputs, Level 3 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Asset	0.7	0.1
Fair Value, Inputs, Level 3 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative liability	0.7	3.7
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	106.4	89.3
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	9.8
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	$ 0.3	2.1
Derivative liability		$ 0.0