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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-01-05</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001231566</rptOwnerCik>
            <rptOwnerName>FISCHER THOMAS J</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>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-01-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2538.8198</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8449.0947</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25969</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Phantom Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F3"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-01-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2538.8198</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>2538.8198</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2538.8198</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Upon the vesting of restricted stock granted to the reporting person on January 3, 2012, the reporting person deferred the receipt of 2,538.8198 shares of common stock and instead received 2,538.8198 phantom stock units pursuant to the Wisconsin Energy Corporation Directors' Deferred Compensation Plan (DDCP). As a result, the reporting person is reporting the disposition of 2,538.8198 shares of common stock in exchange for an equal number of phantom stock units.</footnote>
        <footnote id="F2">Includes shares acquired pursuant to dividend reinvestment in transactions exempt from Section 16 pursuant to Rule 16a-11.</footnote>
        <footnote id="F3">One-for-one.</footnote>
        <footnote id="F4">These phantom stock units were accrued under the DDCP and are to be settled following the reporting person's termination of service as a director.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/Joshua M. Erickson, as Attorney-in-Fact</signatureName>
        <signatureDate>2015-01-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-01-05
0000783325
WISCONSIN ENERGY CORP
WEC
0001231566
FISCHER THOMAS J
231 WEST MICHIGAN STREET
MILWAUKEE,
WI
53203
1
0
0
0
Common Stock
2015-01-05
4
D
0
2538.8198
D
8449.0947
D
Common Stock
25969
I
By Trust
Phantom Stock Units
2015-01-05
4
A
0
2538.8198
A
Common Stock
2538.8198
2538.8198
D
Upon the vesting of restricted stock granted to the reporting person on January 3, 2012, the reporting person deferred the receipt of 2,538.8198 shares of common stock and instead received 2,538.8198 phantom stock units pursuant to the Wisconsin Energy Corporation Directors' Deferred Compensation Plan (DDCP). As a result, the reporting person is reporting the disposition of 2,538.8198 shares of common stock in exchange for an equal number of phantom stock units.
Includes shares acquired pursuant to dividend reinvestment in transactions exempt from Section 16 pursuant to Rule 16a-11.
One-for-one.
These phantom stock units were accrued under the DDCP and are to be settled following the reporting person's termination of service as a director.
/s/Joshua M. Erickson, as Attorney-in-Fact
2015-01-07