DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative assets	$ 72.8	$ 91.5
Derivative liability	32.6	3.7
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	72.8	91.4
Derivative liability	30.2	0.0
Fair Value, Inputs, Level 2 [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	0.0	0.1
Derivative liability	2.4	3.7
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	72.8	91.4
Derivative liability	30.2	0.0
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Derivative Asset [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	0.0	0.1
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 2 [Member] | Designated as Hedging Instrument [Member] | Commodity Contract [Member] | Derivative Liability [Member]
Derivatives, Fair Value [Line Items]
Derivative liability	2.4	3.7
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	71.2	89.3
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	1.6	2.1
Derivative liability	$ 30.2
Valuation, Market Approach [Member] | Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Derivative Liability [Member]
Derivatives, Fair Value [Line Items]
Derivative liability		$ 0.0