Financial and Other Derivative Instruments Financial and Other Derivative Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Assets, Current	$ 90	$ 108
Derivative Assets, Noncurrent	27	39
Derivative Liabilities, Current	(90)	(125)
Derivative Liabilities, Noncurrent	(16)	(26)
Derivative Asset [Member]
Derivative [Line Items]
Derivative Assets, Current	757	862
Derivative Assets, Noncurrent	119	154
Derivative Liabilities [Member]
Derivative [Line Items]
Derivative Liabilities, Current	(750)	(879)
Derivative Liabilities, Noncurrent	(120)	(141)
Counterparty Netting [Member]
Derivative [Line Items]
Derivative Assets, Current	(653)	(754)
Derivative Assets, Noncurrent	(92)	(115)
Derivative Liabilities, Current	653	754
Derivative Liabilities, Noncurrent	92	115
Collateral Adjustment [Member]
Derivative [Line Items]
Derivative Assets, Current	(14)	0
Derivative Assets, Noncurrent	0	0
Derivative Liabilities, Current	7	0
Derivative Liabilities, Noncurrent	12	0
Derivative [Member]
Derivative [Line Items]
Derivative Assets, Current	90	108
Derivative Assets, Noncurrent	27	39
Derivative Liabilities, Current	(90)	(125)
Derivative Liabilities, Noncurrent	$ (16)	$ (26)