Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 16	$ 79
Net realized and unrealized losses (1)	5	18
Purchases	24	0
Issuances	0	(1)
Transfers out of Level 3 to Level 2	0	(1)
Balance as of the end of the period	$ 45	$ 95

Net Liabilities From Price Risk Management Activities Classified as Level 3

No definition available.

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- Definition

Realized and Unrealized Gains and Losses, Net, Commodity Contracts

+ References

No definition available.

+ Details

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- Details

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- Definition

Transfers out of liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy that have taken place during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(3)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

+ Details

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- Definition

Issues that have taken place during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

+ Details

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- Definition

Purchases that have taken place during the period in relation to liabilities measured at fair value and categorized within Level 3 of the fair value hierarchy.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=7578670&loc=d3e19207-110258

+ Details

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