Risk Management Energy Commodity Price Risk Managment (Details)	Sep. 30, 2012
Crude Oil [Member]
Derivative [Line Items]
Net open position long/(short)	(20,500,000)
Natural Gas Fixed Price [Member]
Derivative [Line Items]
Net open position long/(short)	(27,600,000,000)
Natural Gas Basis [Member]
Derivative [Line Items]
Net open position long/(short)	(27,600,000,000)
Net open position long/(short)	(600,000,000)