Disclosures About Derivative Instruments and Hedging Activities (Details)	Sep. 30, 2011 gal	Sep. 30, 2010 gal
LPG [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	138,000,000	160,000,000
Natural Gas [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	26,100,000	36,300,000
Electricity (millions of kilowatt-hours) | Call Option [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	1,219,800,000	1,203,800,000
Electricity (millions of kilowatt-hours) | Put Option [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	204,900,000	0