Quantitative Information about Level 3 Fair Value Measurements (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures [Line Items]
Liability Value	(384)
Stockholder Value Appreciation Program [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Liability Value	(3)
Stockholder Value Appreciation Program [Member] \| Historical [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
SBC Expected Volatility Rate, Maximum	50.20%
Natural gas contracts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative Asset, Fair Value, Total	103
Oil contracts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative Asset, Fair Value, Total	510
Options Held [Member] \| Natural gas contracts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative Asset, Fair Value, Total	41
Options Held [Member] \| Natural gas contracts [Member] \| Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Credit Risk	1.12%
Fair Value Assumptions Expected Volatility Curves	60.53%
Options Held [Member] \| Natural gas contracts [Member] \| Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Credit Risk	0.01%
Fair Value Assumptions Expected Volatility Curves	23.11%
Options Held [Member] \| Oil contracts [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Derivative Liability, Fair Value, Total	422
Options Held [Member] \| Oil contracts [Member] \| Maximum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Credit Risk	1.76%
Fair Value Assumptions Expected Volatility Curves	63.41%
Options Held [Member] \| Oil contracts [Member] \| Minimum [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Credit Risk	0.01%
Fair Value Assumptions Expected Volatility Curves	28.03%

Measure of dispersion, in percentage terms

No definition available.

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- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 4B

-Subparagraph (c)(2)

-URI http://asc.fasb.org/extlink&oid=35706170&loc=SL5624163-113959

+ Details

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- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

+ References

+ Details

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- Definition

Risk associated with risk of default, credit spread risk and downgrade risk, expressed as a percentage, used as an input to measure fair value.

+ 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 (bbb)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ 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)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

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- Definition

The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

+ References

No definition available.

+ Details

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- Details

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