Derivative and Hedging Activities - Derivative Instruments in Balance Sheet Table (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Asset Derivatives:
Short-term derivative assets	$ 0	$ 58
Liability Derivatives:
Total derivative instruments	(649)	(979)
Commodity contracts | Short [Member]
Asset Derivatives:
Short-term derivative assets		58
Asset commodity contracts	29	110
Liability Derivatives:
Liability commodity contracts	231	157
Commodity contracts | Long [Member]
Asset Derivatives:
Asset commodity contracts	11	5
Liability Derivatives:
Liability commodity contracts	362	882
Foreign currency contracts | Short [Member]
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	0	0
Foreign currency contracts | Long [Member]
Asset Derivatives:
Asset commodity contracts	2	0
Liability Derivatives:
Liability commodity contracts	0	20
Interest rate contract | Short [Member]
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	6	0
Interest rate contract | Long [Member]
Asset Derivatives:
Asset commodity contracts	0	0
Liability Derivatives:
Liability commodity contracts	92	35
Designated as Hedging Instrument
Asset Derivatives:
Short-term derivative assets	2	0
Liability Derivatives:
Liability commodity contracts	0	(20)
Designated as Hedging Instrument | Foreign currency contracts
Asset Derivatives:
Short-term derivative assets	2	0
Liability Derivatives:
Liability commodity contracts		(20)
Designated as Hedging Instrument | Foreign currency contracts | Long [Member]
Liability Derivatives:
Liability commodity contracts	0
Not designated as hedging instruments
Asset Derivatives:
Asset commodity contracts	40	115
Liability Derivatives:
Liability commodity contracts	(691)	(1,074)
Not designated as hedging instruments | Commodity contracts | Short [Member]
Asset Derivatives:
Asset commodity contracts	29	110
Liability Derivatives:
Liability commodity contracts	(231)	(157)
Not designated as hedging instruments | Commodity contracts | Long [Member]
Asset Derivatives:
Asset commodity contracts	11	5
Liability Derivatives:
Liability commodity contracts	(362)	(882)
Not designated as hedging instruments | Interest rate contract | Short [Member]
Liability Derivatives:
Liability commodity contracts	(6)	0
Not designated as hedging instruments | Interest rate contract | Long [Member]
Liability Derivatives:
Liability commodity contracts	$ (92)	$ (35)