Derivative Instruments (Details 2) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Derivatives, Fair Value [Line Items]
Derivative assets, current	$ 746	$ 445
Derivative Assets, Noncurrent	236	105
Total derivative assets	982	550
Current derivative liabilities	706	451
Derivative Liabilities, Noncurrent	248	243
Total derivative liabilities	954	694
Net derivative assets (liabilities)	28	(144)
Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	5	9
Total derivative liabilities	119	115
Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	977	541
Total derivative liabilities	835	579
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	0	0
Derivative Assets, Noncurrent	5	9
Total derivative assets	5	9
Current derivative liabilities	47	47
Derivative Liabilities, Noncurrent	83	82
Total derivative liabilities	130	129
Net derivative assets (liabilities)	(125)	(120)
Interest Rate Swap [Member] | Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	5	9
Total derivative liabilities	119	115
Interest Rate Swap [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	0	0
Total derivative liabilities	11	14
Commodity Option [Member]
Derivatives, Fair Value [Line Items]
Derivative assets, current	746	445
Derivative Assets, Noncurrent	231	96
Total derivative assets	977	541
Current derivative liabilities	659	404
Derivative Liabilities, Noncurrent	165	161
Total derivative liabilities	824	565
Net derivative assets (liabilities)	153	(24)
Commodity Option [Member] | Not Designated as Hedging Instrument [Member]
Derivatives, Fair Value [Line Items]
Total derivative assets	977	541
Total derivative liabilities	$ 824	$ 565