Risk Management Energy Commodity Price Risk Managment (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Notional Amount of Interest Rate Fair Value Hedge Derivatives	$ 4,550	$ 5,525
Crude Oil [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Price Risk Fair Value Hedge Derivatives	(22,000,000)
Nonmonetary Notional Amount of Price Risk Derivative Instruments Not Designated as Hedging Instruments	700,000
Crude Oil Basis [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Price Risk Derivative Instruments Not Designated as Hedging Instruments	(2,400,000)
Natural Gas Fixed Price [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Price Risk Fair Value Hedge Derivatives	(32,800,000,000)
Nonmonetary Notional Amount of Price Risk Derivative Instruments Not Designated as Hedging Instruments	(500,000,000)
Natural gas basis [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Price Risk Fair Value Hedge Derivatives	(32,800,000,000)
Nonmonetary Notional Amount of Price Risk Derivative Instruments Not Designated as Hedging Instruments	600,000,000
Natural Gas Basis [Member]
Derivative [Line Items]
Nonmonetary Notional Amount of Price Risk Derivative Instruments Not Designated as Hedging Instruments	500,000