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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2011-08-08</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>2011-08-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3430.73</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>52.31</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>27561.81</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents the weighted average sale price of the shares of Consolidated Edison, Inc. (the &quot;Company&quot;) common stock sold by the reporting person.  The shares were sold in multiple transactions at prices ranging from $52.30  to $52.33, inclusive.  The reporting person will provide the Company, any security holder of the Company, or the staff of the Securities and Exchange Commission, upon request, full information regarding the numbers of shares purchased at each separate price within the ranges set forth in this footnote (1) of this Form 4.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Carole Sobin;   Attorney-in-Fact</signatureName>
        <signatureDate>2011-08-09</signatureDate>
    </ownerSignature>
</ownershipDocument>
