Derivative Instruments and Hedging Activities Notional Contracts by Derivative Type (Details)	3 Months Ended
	Dec. 31, 2015 MMBTU bbl
Forward Contracts [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	525,000
Forward Contracts [Member] | Price Risk Derivative [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	525,000
Produced Gasoline Member | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	625,000
Produced Gasoline Member | Price Risk Derivative [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	625,000
Commodity Contract [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	11,712,000
Commodity Contract [Member] | Economic Hedges [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	11,712,000
Natural Gas - Short [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	19,200,000
Natural Gas - Short [Member] | Economic Hedges [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
Natural Gas - Short [Member] | Economic Hedges [Member] | Maturing in Year Two [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
Natural Gas - long [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	19,200,000
Natural Gas - long [Member] | Price Risk Derivative [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
Natural Gas - long [Member] | Price Risk Derivative [Member] | Maturing in Year Two [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
Natural Gas - long [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	19,200,000
Natural Gas - long [Member] | Economic Hedges [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
Natural Gas - long [Member] | Economic Hedges [Member] | Maturing in Year Two [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Energy Measure | MMBTU	9,600,000
NYMEX WTI Short [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	1,840,000
NYMEX WTI Short [Member] | Economic Hedges [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	1,840,000
Natural Gas [Member] | Economic Hedges [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	20,616,000
Natural Gas [Member] | Economic Hedges [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	10,308,000
Natural Gas [Member] | Economic Hedges [Member] | Maturing in Year Two [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	10,308,000
Physical Contracts - Long [Member] | Price Risk Derivative [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	38,000
Physical Contracts - Long [Member] | Price Risk Derivative [Member] | Maturing in Next Twelve Months [Member]
economic hedges by derivative type [Line Items]
Derivative, Nonmonetary Notional Amount, Volume	38,000