Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
Jun. 30, 2012	Apr. 30, 2012	Mar. 31, 2012	Jun. 30, 2012
Amortization Expense By Geographic Segment [Line Items]
Write-down of the carrying value of Oil and Gas properties	$ 641	$ 521	$ 521
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	641
Write-down of the carrying value of Oil and Gas properties, net of tax			390	480
Write down of oil and gas property Excluding the effect of cash flow hedge Before Tax	744		656	744
Write down of oil and gas property Excluding the effect of cash flow hedge Net of Tax			$ 491	557

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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.

+ Details

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- Definition

Unamortized costs capitalized less related deferred income taxes exceed ceiling limitation expense net of tax.

+ References

No definition available.

+ Details

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- Definition

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 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

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

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 12

-Section D

-Paragraph b

-Subsection 3

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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

-Section 10

-Paragraph c

-Subparagraph 4(ii)

-Article 4

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