Derivative Instruments (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 445	$ 339
Derivative Asset, Noncurrent	105	98
Total derivative assets	550	437
Derivative Liability, Current	451	357
Derivative Liability, Noncurrent	243	293
Derivative Liability, Fair Value, Gross Liability	694	650
Net derivative assets (liabilities)	(144)	(213)
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	9	4
Derivative Liability, Fair Value, Gross Liability	115	184
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	541	433
Derivative Liability, Fair Value, Gross Liability	579	466
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0	0
Derivative Asset, Noncurrent	9	4
Total derivative assets	9	4
Derivative Liability, Current	47	40
Derivative Liability, Noncurrent	82	160
Derivative Liability, Fair Value, Gross Liability	129	200
Net derivative assets (liabilities)	(120)	(196)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	9	4
Derivative Liability, Fair Value, Gross Liability	115	184
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	0	0
Derivative Liability, Fair Value, Gross Liability	14	16
Commodity Option [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	445	339
Derivative Asset, Noncurrent	96	94
Total derivative assets	541	433
Derivative Liability, Current	404	317
Derivative Liability, Noncurrent	161	133
Derivative Liability, Fair Value, Gross Liability	565	450
Net derivative assets (liabilities)	(24)	(17)
Commodity Option [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	541	433
Derivative Liability, Fair Value, Gross Liability	$ 565	$ 450