Supplementary Oil and Gas Disclosure (Unaudited) - (Textuals) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 MMBoe	Dec. 31, 2013 MMBoe	Dec. 31, 2012 MMBoe
Costs Incurred, Asset Retirement Obligation Incurred	$ 56	$ 121	$ 9
Years experience employee overseeing reserve estimation is greater than	30 years 0 months 0 days
Years reserve estimation experience	20 years 0 months 0 days
Proved Reserves Extensions, Discoveries, Additions and Purchase of Minerals in Place	81	82	86
Percentage of Liquids Comprising Proved Reserves	58.00%	55.00%	48.00%
Net effect of proved reserve revisions, additions and purchases	132
Percentage of drillling additions related out major, domestic resource plays	99.00%
Proved Undeveloped Reserves Additions	52nfx_ProvedUndevelopedReservesAdditions
Proved developed liquids additions	54
Proved Reserve Revisions Percentage of Beginning Reserves	8.00%
Proved Reserves Price Related Revisions	3nfx_ProvedReservesPriceRelatedRevisions
Proved Reserve Revisions Development	77nfx_ProvedReservesRevisionsDevelopment
Proved Reserves Performance Related Revisions	29

Net effect of proved reserve revisions, additions and purchases

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- Definition

Percentage of drilling additions related to our major, domestic resource plays in the Mid-Continent, Rocky Mountains and South Texas

+ References

No definition available.

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- Definition

Percent of proved reserves that are oil, condensate and NGLs.

+ References

No definition available.

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Additions to proved developed oil, condensate and NGL reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reserves of proved reserves in old fields and purchases of minerals in place.

+ References

No definition available.

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Proved reserve revisions percentage of beginning of period reserves.

+ References

No definition available.

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Additions to proved reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reserves of proved reserves in old fields and purchases of minerals in place.

+ References

No definition available.

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- Definition

Performance related revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history.

+ References

No definition available.

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- Definition

Price revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from change in economic factors (price).

+ References

No definition available.

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- Definition

Development revisions represent changes in previous estimates of proved reserves, either upward or downward, resulting from new information (except for an increase in proved acreage) normally obtained from development drilling and production history.

+ References

No definition available.

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- Definition

Additions to proved undeveloped reserves that result from (1) extension of the proved acreage of previously discovered (old) reservoirs through additional drilling in periods after discovery and (2) discovery of new fields with proved reserves or of new reserves of proved reserves in old fields and purchases of minerals in place.

+ References

No definition available.

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- Definition

Number of years experience of the technical employee overseeing the reserve estimation is greater than.

+ References

No definition available.

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Number of years of reserve estimation experience of the technical employee overseeing the reserve estimation is greater than.

+ References

No definition available.

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- Definition

Amount of asset retirement obligations (ARO) costs incurred (whether capitalized or charged to expense) during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849

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