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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-06-08</periodOfReport>

    <issuer>
        <issuerCik>0000783325</issuerCik>
        <issuerName>WISCONSIN ENERGY CORP</issuerName>
        <issuerTradingSymbol>WEC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001041958</rptOwnerCik>
            <rptOwnerName>CULVER CURT S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>231 WEST MICHIGAN STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>MILWAUKEE,</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>53203</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2009-06-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>30.8489</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>40.52</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>30.8489</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13970.5448</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">One-for-one.</footnote>
        <footnote id="F2">These phantom stock units were acquired pursuant to a deferral of director fees in an acquisition exempt from Section 16(b) pursuant to Rule 16b-3(d).</footnote>
        <footnote id="F3">These phantom stock units were accrued under the WEC Directors' Deferred Compensation Plan (&quot;DDCP&quot;) and are to be settled  following the reporting person's termination of service as a director.</footnote>
        <footnote id="F4">Includes phantom stock units accrued pursuant to a dividend reinvestment feature of the DDCP in transactions exempt from Section 16 pursuant to Rule 16a-11.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Joshua M. Erickson, as Attorney-in-Fact</signatureName>
        <signatureDate>2009-06-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2009-06-08
0000783325
WISCONSIN ENERGY CORP
WEC
0001041958
CULVER CURT S
231 WEST MICHIGAN STREET
MILWAUKEE,
WI
53203
1
0
0
0
Phantom Stock Units
2009-06-08
4
A
0
30.8489
40.52
A
Common Stock
30.8489
13970.5448
D
One-for-one.
These phantom stock units were acquired pursuant to a deferral of director fees in an acquisition exempt from Section 16(b) pursuant to Rule 16b-3(d).
These phantom stock units were accrued under the WEC Directors' Deferred Compensation Plan ("DDCP") and are to be settled  following the reporting person's termination of service as a director.
Includes phantom stock units accrued pursuant to a dividend reinvestment feature of the DDCP in transactions exempt from Section 16 pursuant to Rule 16a-11.
/s/ Joshua M. Erickson, as Attorney-in-Fact
2009-06-10