Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified			3 Months Ended	6 Months Ended
Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Commodity Contract [Member]	Jun. 30, 2011 Commodity Contract [Member]	Jun. 30, 2012 Commodity Contract [Member]	Jun. 30, 2011 Commodity Contract [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments Not Designated as Hedging Instruments, Gain (Loss), Net			$ (718)	$ 33	$ (535)	$ 80
Derivative, Collateral, Right to Reclaim Cash	$ 350	$ 30

Net gain (loss) from the increase (decrease) in fair value of derivative instrument not designated as hedging instrument.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4C

-Subparagraph (e)

-URI http://asc.fasb.org/extlink&oid=7476318&loc=SL5624171-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 133

-Paragraph 45

-Subparagraph b(1)(b)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration