<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-01-30</periodOfReport>

    <issuer>
        <issuerCik>0000072207</issuerCik>
        <issuerName>NOBLE ENERGY INC</issuerName>
        <issuerTradingSymbol>NBL</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001417340</rptOwnerCik>
            <rptOwnerName>Robison Andrea Lee</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1001 NOBLE ENERGY WAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77070</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>Sr. VP Human Resources &amp; Admin</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-01-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>436</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>32.37</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>64894</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-01-31</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>638</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>32.37</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>64256</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3320</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>60936</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>892</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>31.65</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>60044</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4502</value>
                    <footnoteId id="F5"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>64546</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>9004</value>
                    <footnoteId id="F6"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>73550</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Noble Energy, Inc. Common Stock</value>
                <footnoteId id="F7"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2356</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>401(k)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Non-Qualified Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>31.65</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>28217</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F8"/>
            </exerciseDate>
            <expirationDate>
                <value>2026-02-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Noble Energy, Inc. Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>28217</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28217</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F9"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4502</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2018-02-01</value>
            </exerciseDate>
            <expirationDate>
                <value>2018-02-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Noble Energy, Inc. Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4502</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F10"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2016-02-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>9004</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2019-02-01</value>
            </exerciseDate>
            <expirationDate>
                <value>2019-02-01</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Noble Energy, Inc. Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>9004</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Reflects shares relinquished to Noble Energy, Inc. by the reporting person out of, and to cover estimated tax withholding for, restricted shares granted on January 30, 2015, and vesting on January 30, 2016. The stock price reflected in Table I Column 4 was determined based on &quot;fair market value,&quot; defined in the 1992 Stock Option and Restricted Stock Plan, as amended and restated (1992 Plan) for this transaction as the closing trading price of Noble Energy, Inc. common stock on the NYSE on January 29, 2016.</footnote>
        <footnote id="F2">Reflects shares relinquished to Noble Energy, Inc. by the reporting person out of, and to cover estimated tax withholding for, restricted shares granted on January 31, 2014, and vesting on January 31, 2016. The stock price reflected in Table I Column 4 was determined based on &quot;fair market value,&quot; defined in the 1992 Plan for this transaction as the closing trading price of Noble Energy, Inc. common stock on the NYSE on January 29, 2016.</footnote>
        <footnote id="F3">Reflects unvested shares of performance restricted stock granted on February 1, 2013 forfeited to Noble Energy, Inc. on February 1, 2016.</footnote>
        <footnote id="F4">Reflects shares relinquished to Noble Energy, Inc. by the reporting person out of, and to cover estimated tax withholding for, restricted shares granted on February 1, 2013, and vesting on February 1, 2016. The stock price reflected in Table I Column 4 was determined based on &quot;fair market value,&quot; defined in the 1992 Plan for this transaction as the closing trading price of Noble Energy, Inc. common stock on the NYSE on February 1, 2016.</footnote>
        <footnote id="F5">Restricted shares of Noble Energy, Inc. Common Stock will vest 80% one year after the date of grant and the remaining 20% two years after the date of grant, granted under the 1992 Plan.</footnote>
        <footnote id="F6">Performance restricted stock will vest three years after the date of grant upon, and subject to a formula related to, the Company's achievement of certain levels of total shareholder return (TSR) relative to a pre-determined industry peer group, granted under the 1992 Plan.</footnote>
        <footnote id="F7">Holdings under the Company's 401(k) Plan are reported in units by the plan administrator. The units represent shares of Company common stock. The number of shares represented by the units is based upon the plan statement as of November 1, 2007 and calculated by dividing the aggregate unit balance under the 401(k) by the closing price of the Company's common stock on that date.</footnote>
        <footnote id="F8">The option is exercisable in three equal annual installments beginning one year after the date of grant.</footnote>
        <footnote id="F9">Each phantom unit is the economic equivalent of one share of Noble Energy, Inc. Common Stock to be settled in cash upon vesting and subject to a maximum settlement value of $126.60 per unit plus the equivalent value of accrued and unpaid dividends. Phantom units were granted under the 1992 Plan and will vest 100% two years after the date of grant.</footnote>
        <footnote id="F10">Each phantom unit is the economic equivalent of one share of Noble Energy, Inc. Common Stock, to be settled in cash upon vesting and subject to a maximum settlement value of $126.60 per unit plus the equivalent value of accrued and unpaid dividends. Phantom units were granted under the 1992 Plan and will vest three years after the date of grant upon, and subject to a formula related to, the Company's achievement of certain levels of total shareholder return (TSR) relative to a pre-determined industry peer group.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Aaron G. Carlson, Attorney-in-Fact</signatureName>
        <signatureDate>2016-02-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
