Quarterly report pursuant to Section 13 or 15(d)

DERIVATIVE INSTRUMENTS (Narrative) (Details)

v3.10.0.1
DERIVATIVE INSTRUMENTS (Narrative) (Details)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
gal
MMcf
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
gal
MMcf
Sep. 30, 2017
USD ($)
Jan. 01, 2018
USD ($)
Dec. 31, 2017
USD ($)
gal
MMcf
Derivative [Line Items]            
Derivative assets $ 190.8   $ 190.8   $ 49.5 $ 37.9
Derivative liability 5.8   5.8     2.0
Not Designated as Hedging Instrument [Member]            
Derivative [Line Items]            
Derivative assets 190.6   190.6     37.9
Derivative liability $ 5.7   $ 5.7     $ 1.7
Natural Gas [Member]            
Derivative [Line Items]            
Investment Contract Volume | MMcf 3,600,000.0   3,600,000.0     3,500,000.0
Diesel [Member]            
Derivative [Line Items]            
Investment Contract Volume | gal 1,400,000.0   1,400,000.0     0
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member]            
Derivative [Line Items]            
Amount of gain/(loss) recognized in income on derivative $ 139.7 $ 54.3 $ 337.1 $ 123.9    
Customer Supply Agreement [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Derivative assets 186.0   186.0     $ 37.9
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Product Revenues [Member]            
Derivative [Line Items]            
Amount of gain/(loss) recognized in income on derivative (3.8) $ (15.7) (2.7) $ (21.0)    
Provisional Pricing Arrangements [Member] | Not Designated as Hedging Instrument [Member] | Derivative Financial Instruments, Assets [Member]            
Derivative [Line Items]            
Derivative assets $ 4.6   $ 4.6     $ 0.0