Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details)

v3.10.0.1
DERIVATIVE INSTRUMENTS (Schedule Of Derivative Instruments In Statement Of Financial Position, Fair Value) (Details) - USD ($)
$ in Millions
Sep. 30, 2018
Jan. 01, 2018
Dec. 31, 2017
Derivatives, Fair Value [Line Items]      
Derivative assets $ 190.8 $ 49.5 $ 37.9
Derivative liability 5.8   2.0
Not Designated as Hedging Instrument [Member]      
Derivatives, Fair Value [Line Items]      
Derivative assets 190.6   37.9
Derivative liability 5.7   1.7
Not Designated as Hedging Instrument [Member] | Customer Supply Agreement [Member] | Derivative Financial Instruments, Assets [Member]      
Derivatives, Fair Value [Line Items]      
Derivative assets 186.0   37.9
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Derivative Financial Instruments, Assets [Member]      
Derivatives, Fair Value [Line Items]      
Derivative assets 4.6   0.0
Not Designated as Hedging Instrument [Member] | Provisional Pricing Arrangements [Member] | Other Current Liabilities [Member]      
Derivatives, Fair Value [Line Items]      
Derivative liability 5.7   1.7
Fair Value, Inputs, Level 3 [Member]      
Derivatives, Fair Value [Line Items]      
Derivative assets 190.6   37.9
Derivative liability 5.7   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 0.2   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