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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2005-04-01</periodOfReport>

    <issuer>
        <issuerCik>0001141982</issuerCik>
        <issuerName>COOPER INDUSTRIES LTD</issuerName>
        <issuerTradingSymbol>CBE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001200003</rptOwnerCik>
            <rptOwnerName>EVANS IVOR J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>UNION PACIFIC RAILROAD COMPANY</rptOwnerStreet1>
            <rptOwnerStreet2>1400 DODGE STREET, 19TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>OMAHA</rptOwnerCity>
            <rptOwnerState>NE</rptOwnerState>
            <rptOwnerZipCode>68179</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2005-04-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>254</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>71.44</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5532</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents unissued shares earned pursuant to the Directors' Retainer Fee Stock Plan.</footnote>
        <footnote id="F2">Includes 16 unissued shares for dividend equivalents credited April 1, 2005 pursuant to the Amended and Restated Directors' Stock Plan and 11 unissued shares for dividend equivalents credited April 1, 2005 pursuant to the Directors' Retainer Fee Stock Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Barbara A. Widra, Attorney-in-Fact</signatureName>
        <signatureDate>2005-04-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
