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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-06-30</periodOfReport>

    <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>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2011-06-30</value>
            </transactionDate>
            <deemedExecutionDate>
                <value>2011-07-06</value>
            </deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>21.22</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>52.35</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>30971.76</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Purchase of shares of common stock of Consolidated Edison, Inc. (the &quot;Company&quot;) under the Company's Stock Purchase Plan.</footnote>
        <footnote id="F2">Includes 270.22 Deferred Stock Units (&quot;DSU&quot;) acquired in June 15, 2011 pursuant to the Company Long Term Incentiv Plan's dividend reinvestment provision.  Each DSU represents one share of the Company's common stock. Also includes 3.76 shares of Company common stock acquired in June 30, 2011 pursuant to the Company Automatic Dividend Reinvestment and Cash Payment Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Carole Sobin;   Attorney-in-Fact</signatureName>
        <signatureDate>2011-07-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
