Derivative and Hedging Activities Derivative Instruments in Balance Sheet (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Liability Derivatives:
Total derivative instruments	$ (543)	$ (979)
Commodity contracts | Short-term derivative instruments
Asset Derivatives:
Asset commodity contracts	159	110
Liability Derivatives:
Liability commodity contracts	(109)	(52)
Commodity contracts | Long-term derivative instruments
Asset Derivatives:
Asset commodity contracts	61	5
Liability Derivatives:
Liability commodity contracts	(54)	(3)
Foreign currency contracts | Short-term derivative instruments
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Foreign currency contracts | Long-term derivative instruments
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Interest rate contract | Short-term derivative instruments
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Interest rate contract | Long-term derivative instruments
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Designated as Hedging Instrument
Liability Derivatives:
Liability commodity contracts	(27)	(20)
Designated as Hedging Instrument | Foreign currency contracts | Long-term derivative instruments
Liability Derivatives:
Liability commodity contracts	(27)	(20)
Not designated as hedging instruments
Asset Derivatives:
Asset commodity contracts	220	115
Liability Derivatives:
Liability commodity contracts	(736)	(1,074)
Not designated as hedging instruments | Commodity contracts | Short-term derivative instruments
Asset Derivatives:
Asset commodity contracts	159	110
Liability Derivatives:
Liability commodity contracts	(163)	(157)
Not designated as hedging instruments | Commodity contracts | Long-term derivative instruments
Asset Derivatives:
Asset commodity contracts	61	5
Liability Derivatives:
Liability commodity contracts	(482)	(882)
Not designated as hedging instruments | Interest rate contract | Long-term derivative instruments
Liability Derivatives:
Liability commodity contracts	$ (91)	$ (35)