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

    <schemaVersion>X0303</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2008-12-31</periodOfReport>

    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0001047862</issuerCik>
        <issuerName>CONSOLIDATED EDISON INC</issuerName>
        <issuerTradingSymbol>ED</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001232649</rptOwnerCik>
            <rptOwnerName>Hernandez Sally</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>CONSOLIDATED EDISON, INC. C/O SECRETARY</rptOwnerStreet1>
            <rptOwnerStreet2>4 IRVING PLACE, ROOM 1618-S</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10003</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>22614.8</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Includes 233.80 and 265.58 Deferred Stock Units acquired on September 15, 2008 and December 15, 2008, respectively, pursuant to the Consolidated Edison, Inc. (&quot;Company&quot;) Long Term Incentive Plan's dividend reinvestment provision.  Also includes 3.9177, 4.0482, 3.7399, and 4.3473 shares of Company common stock acquired on March 15, 2008, June 15, 2008, September 15, 2008 and December 15, 2008, respectively, pursuant to the Company Automatic Dividend Reinvestment and Cash Payment Plan.  As per General Instruction 4(a) to Form 5, Column 5 sets forth the number of securities beneficially owned by the reporting person as of December 31, 2008.  As of the filing date of this report, the number of securities beneficially owned by the reporting person is 22,643.17, reflecting certain transactions previously reported on Form 4 filing(s) during the period between December 31, 2008 and the filing date of this report.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Peter J. Barrett; Attorney-in-Fact</signatureName>
        <signatureDate>2009-02-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
