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=64837297&loc=SL5624163-113959

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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=66048111&loc=d3e19207-110258

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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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=66048111&loc=d3e19207-110258

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Quantitative Information about Level 3 Fair Value Measurements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Liability Value	$ (75)	$ (308)	$ (384)
Natural gas contracts [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative Liability, Fair Value, Total	(54)
Natural gas contracts [Member] \| Options Held [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative Liability, Fair Value, Total	$ (29)
Natural gas contracts [Member] \| Options Held [Member] \| Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Credit Risk	0.01%
Fair Value Assumptions Expected Volatility Curves	23.53%
Natural gas contracts [Member] \| Options Held [Member] \| Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Credit Risk	1.45%
Fair Value Assumptions Expected Volatility Curves	53.39%
Oil contracts [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative Asset, Fair Value, Total	$ 29
Oil contracts [Member] \| Options Held [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Derivative Liability, Fair Value, Total	$ (46)
Oil contracts [Member] \| Options Held [Member] \| Minimum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Credit Risk	0.01%
Fair Value Assumptions Expected Volatility Curves	23.13%
Oil contracts [Member] \| Options Held [Member] \| Maximum [Member]
Fair Value Inputs, Liabilities, Quantitative Information [Line Items]
Credit Risk	1.45%
Fair Value Assumptions Expected Volatility Curves	66.50%