DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Derivatives, Fair Value [Line Items]
Derivative assets	$ 174.7	$ 49.5	$ 37.9
Derivative Liability	3.1		2.0
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	174.6		37.9
Derivative Liability	3.0		1.7
Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	169.4		37.9
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Derivative Financial Instruments, Assets [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	5.2		0.0
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	3.0		1.7
Fair Value, Inputs, Level 3 [Member]
Derivatives, Fair Value [Line Items]
Derivative assets	174.6		37.9
Derivative Liability	3.0		1.7
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 assets	0.1		0.0
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	0.1		0.3
Fair Value, Inputs, Level 3 [Member] | Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Other Current Liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liability	$ 0.0		$ 0.0