Disclosures About Derivative Instruments and Hedging Activities (Details)	Jun. 30, 2012 gal	Jun. 30, 2011 gal
LPG (millions of gallons) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	231,900,000	145,000,000
Natural gas (millions of dekatherms) [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	21,200,000	21,200,000
Electricity (millions of kilowatt-hours) [Member] | Calls [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	1,688,400,000	1,318,000,000
Electricity (millions of kilowatt-hours) [Member] | Puts [Member]
Outstanding derivative commodity instruments volumes
Outstanding derivative commodity instruments volumes	131,800,000	117,200,000