Disclosures About Derivative Instruments and Hedging Activities (Details)	Sep. 30, 2012 gal	Sep. 30, 2011 gal
LPG (millions of gallons) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	243,900,000	138,000,000
Natural Gas (millions of kilowatt hours) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	23,600,000	26,100,000
Electricity (millions of kilowatt-hours) [Member] | Call Option [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	1,415,700,000	1,219,800,000
Electricity (millions of kilowatt-hours) [Member] | Put Option [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	135,300,000	204,900,000