Financial and Other Derivative Instruments Financial and Other Derivative Instruments (Details 2) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Derivative [Line Items]
Derivative Assets, Current	$ 56	$ 108
Derivative Assets, Noncurrent	17	39
Derivative Liabilities, Current	81	125
Derivative Liabilities, Noncurrent	14	26
Derivative Asset [Member]
Derivative [Line Items]
Derivative Assets, Current	775	862
Derivative Assets, Noncurrent	95	154
Derivative Liabilities [Member]
Derivative [Line Items]
Derivative Liabilities, Current	(856)	(879)
Derivative Liabilities, Noncurrent	(88)	(141)
Counterparty Netting [Member]
Derivative [Line Items]
Derivative Assets, Current	(719)	(754)
Derivative Assets, Noncurrent	(74)	(115)
Derivative Liabilities, Current	719	754
Derivative Liabilities, Noncurrent	74	115
Collateral Adjustment [Member]
Derivative [Line Items]
Derivative Assets, Current	0	0
Derivative Assets, Noncurrent	(4)	0
Derivative Liabilities, Current	56	0
Derivative Liabilities, Noncurrent	0	0
Derivative [Member]
Derivative [Line Items]
Derivative Assets, Current	56	108
Derivative Assets, Noncurrent	17	39
Derivative Liabilities, Current	(81)	(125)
Derivative Liabilities, Noncurrent	$ (14)	$ (26)