Derivative and Hedging Activities Derivative Instruments in Balance Sheet Table (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Liability Derivatives:
Total derivative instruments	$ (676)	$ (979)
Commodity contracts
Asset Derivatives:
Asset commodity contracts	115	110
Commodity contracts | Short [Member]
Liability Derivatives:
Liability commodity contracts	104	52
Commodity contracts | Long [Member]
Asset Derivatives:
Asset commodity contracts	11	5
Liability Derivatives:
Liability commodity contracts	9	3
Foreign currency contracts
Asset Derivatives:
Asset commodity contracts	0	0
Foreign currency contracts | Short [Member]
Liability Derivatives:
Liability commodity contracts	0	0
Foreign currency contracts | Long [Member]
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Interest rate contract
Asset Derivatives:
Asset commodity contracts	0	0
Interest rate contract | Short [Member]
Liability Derivatives:
Liability commodity contracts	0	0
Interest rate contract | Long [Member]
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Designated as Hedging Instrument
Liability Derivatives:
Liability commodity contracts	(5)	(20)
Designated as Hedging Instrument | Foreign currency contracts
Liability Derivatives:
Liability commodity contracts		(20)
Designated as Hedging Instrument | Foreign currency contracts | Long [Member]
Liability Derivatives:
Liability commodity contracts	(5)
Not designated as hedging instruments
Asset Derivatives:
Asset commodity contracts	126	115
Liability Derivatives:
Liability commodity contracts	(797)	(1,074)
Not designated as hedging instruments | Commodity contracts | Short [Member]
Asset Derivatives:
Asset commodity contracts	115	110
Liability Derivatives:
Liability commodity contracts	(265)	(157)
Not designated as hedging instruments | Commodity contracts | Long [Member]
Asset Derivatives:
Asset commodity contracts	11	5
Liability Derivatives:
Liability commodity contracts	(444)	(882)
Not designated as hedging instruments | Interest rate contract | Short [Member]
Liability Derivatives:
Liability commodity contracts	(9)	0
Not designated as hedging instruments | Interest rate contract | Long [Member]
Liability Derivatives:
Liability commodity contracts	$ (79)	$ (35)