Derivative Instruments (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 655	$ 445
Derivative Assets, Noncurrent	174	105
Total derivative assets	829	550
Current derivative liabilities	728	451
Derivative Liabilities, Noncurrent	230	243
Total derivative liabilities	958	694
Net derivative assets (liabilities)	(129)	(144)
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	7	9
Total derivative liabilities	113	115
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	822	541
Total derivative liabilities	845	579
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0	0
Derivative Assets, Noncurrent	7	9
Total derivative assets	7	9
Current derivative liabilities	47	47
Derivative Liabilities, Noncurrent	79	82
Total derivative liabilities	126	129
Net derivative assets (liabilities)	(119)	(120)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	7	9
Total derivative liabilities	113	115
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	0	0
Total derivative liabilities	13	14
Commodity Option [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	655	445
Derivative Assets, Noncurrent	167	96
Total derivative assets	822	541
Current derivative liabilities	681	404
Derivative Liabilities, Noncurrent	151	161
Total derivative liabilities	832	565
Net derivative assets (liabilities)	(10)	(24)
Commodity Option [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	822	541
Total derivative liabilities	$ 832	$ 565