Financial and Other Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	$ 876	$ 1,016
Derivative Liability Fair Value Gross Liability	(870)	(1,020)
Derivative Assets, Current	90	108
Derivative Assets, Noncurrent	27	39
Derivative Liabilities, Current	90	125
Derivative Liabilities, Noncurrent	16	26
Estimate of Fair Value, Fair Value Disclosure [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	757	862
Derivative Assets, Noncurrent	119	154
Derivative Liabilities, Current	(750)	(879)
Derivative Liabilities, Noncurrent	(120)	(141)
Derivative [Member]
Derivatives designated as hedging instruments:
Derivative Assets, Current	90	108
Derivative Assets, Noncurrent	27	39
Derivative Liabilities, Current	90	125
Derivative Liabilities, Noncurrent	16	26
Designated as Hedging Instrument [Member] | Interest rate contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	0	0
Derivative Liability Fair Value Gross Liability	0	(1)
Not Designated as Hedging Instrument [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	876	1,016
Derivative Liability Fair Value Gross Liability	(870)	(1,019)
Not Designated as Hedging Instrument [Member] | Foreign currency exchange contracts [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	0	0
Derivative Liability Fair Value Gross Liability	(1)	0
Not Designated as Hedging Instrument [Member] | Natural Gas [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	504	645
Derivative Liability Fair Value Gross Liability	(510)	(661)
Not Designated as Hedging Instrument [Member] | Electricity [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	317	360
Derivative Liability Fair Value Gross Liability	(307)	(351)
Not Designated as Hedging Instrument [Member] | Other [Member]
Derivatives designated as hedging instruments:
Derivative Asset Fair Value Gross Asset	55	11
Derivative Liability Fair Value Gross Liability	$ (52)	$ (7)