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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-01-03</periodOfReport>

    <issuer>
        <issuerCik>0001004980</issuerCik>
        <issuerName>PG&amp;E CORP</issuerName>
        <issuerTradingSymbol>PCG</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001221221</rptOwnerCik>
            <rptOwnerName>RAMBO BARBARA L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2425 GREEN STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SAN FRANCISCO,</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>94123</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>800</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2639.41</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>800.64</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3440.05</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Restricted shares granted under the PG&amp;E Corporation 2006 Long-Term Incentive Plan (LTIP).</footnote>
        <footnote id="F2">Restricted Stock Units granted under the PG&amp;E Corporation 2006 LTIP.  Restricted Stock Units are payable in common stock on a one-for-one basis upon a director's death, disability, retirement, or a change in control, as defined in the PG&amp;E Corporation 2006 LTIP.</footnote>
        <footnote id="F3">This total includes 931.41 units of phantom stock granted under the PG&amp;E Corporation Non-Employee Director Stock Incentive Plan (SIP), and reflects the acquisition of 7.99 units of phantom stock on April 15, 2005, 7.37 units of phantom stock on July 15, 2005, and 7.51 units of phantom stock on October 17, 2005, pursuant to a dividend reinvestment feature of the SIP.  This total also includes 800.64 Restricted Stock Units granted under the PG&amp;E Corporation 2006 LTIP.  The phantom stock units and the Restricted Stock Units are automatically payable in stock only.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Eric Montizambert, Attorney-in-Fact for Barbara L. Rambo (signed Power of Attorney on file with SEC)</signatureName>
        <signatureDate>2006-01-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
