Outstanding Natural Gas Contracts That Are Not Designated for Hedge Accounting (Details) (Natural gas contracts [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014
Derivative [Line Items]
Derivative Asset, Fair Value, Total	$ 103
Collars [Member] \| Year2015 [Member]
Derivative [Line Items]
Natural Gas Volumes	38,325,000
Derivative, Weighted Average Floor Price	3.93
Derivative, Weighted Average Ceiling Price	4.74
Derivative Asset, Fair Value, Total	36
Fixed-price swaps \| Year2015 [Member]
Derivative [Line Items]
Natural Gas Volumes	49,275,000
Derivative, Swap Type, Average Fixed Price	4.28
Derivative Asset, Fair Value, Total	$ 62

Natural gas volumes in Mmbtus

No definition available.

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- Definition

The average cap rate on a group of price risk derivatives such as caps or collars. A payment or receipt is triggered if the market rate exceeds the cap rate on the contract.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Definition

The average floor rate on a group of price risk derivatives such as floors or collars. A payment or receipt is triggered if the market rate falls below the floor rate on the contract.

+ References

No definition available.

+ Details

Name:	us-gaap_DerivativeAverageFloorPrice
Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- 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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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_DerivativeLineItems
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Balance Type:	na
Period Type:	duration

- Definition

Average fixed price related to the group of price risk swap derivatives.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	us-types:perUnitItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DerivativeByNatureAxis=nfx_CollarsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeByNatureAxis=us-gaap_SwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: