Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2012
Summary of Significant Accounting Policies (Textual) [Abstract]
Discount rate of after-tax future net cash flows	10.00%
United States And Canada [Member]
Amortization Expense By Geographic Segment [Line Items]
Write-down of the carrying value of Oil and Gas properties	521
Write-down of the carrying value of Oil and Gas properties, net of tax	390
Write down of oil and gas property Excluding the effect of cash flow hedge Before Tax	656
Write down of oil and gas property Excluding the effect of cash flow hedge Net of Tax	491

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Discount rate of after-tax future net cash flows.

+ References

No definition available.

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- Definition

Effects of cash flow hedges not considered in calculating ceiling limitation amount net of tax.

+ References

No definition available.

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- Definition

Unamortized costs capitalized less related deferred income tax exceed ceiling limitations.

+ References

No definition available.

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- Definition

The dollar amount that would have been charged to income had the effects of the cash flow hedges not been considered in calculating the ceiling limitation at an oil and gas producing company subject to the full cost rules.

+ References

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 12

-Section D

-Paragraph b

-Subsection 3

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 932

-SubTopic 360

-Section S99

-Paragraph 2

-Subparagraph (SAB TOPIC 12.D.3(b))

-URI http://asc.fasb.org/extlink&oid=6601679&loc=d3e516453-122869

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- Definition

The excess of unamortized costs capitalized within a cost center, less related deferred income taxes, over the cost center ceiling limitation, which is charged to expense for oil and gas producing companies that use full cost method of accounting for investments in oil and gas producing properties.

+ References

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 4

-Section 10

-Paragraph c

-Subparagraph 4(ii)

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