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

    <schemaVersion>X0304</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-01-03</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001196937</rptOwnerCik>
            <rptOwnerName>BERGSTROM JOHN F</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>2012-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>2294</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>17563.7084</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2012-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3905.3818</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13658.3266</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6000</value>
                    <footnoteId id="F4"/>
                </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="F5"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2012-01-03</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3905.3818</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F6"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>3905.3818</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>37649.3059</value>
                    <footnoteId id="F7"/>
                    <footnoteId id="F8"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Includes shares acquired pursuant to a dividend reinvestment feature of Wisconsin Energy Corporation's Stock Plus Investment Plan in transactions exempt from Section 16 pursuant to Rule 16a-11.</footnote>
        <footnote id="F2">Upon the vesting of restricted stock granted to the reporting person on January 2, 2009, the reporting person deferred the receipt of 3,905.3818 shares of common stock and instead received 3,905.3818 phantom stock units pursuant to the WEC Directors' Deferred Compensation Plan (DDCP).  As a result, the reporting person is reporting the disposition of 3,905.3818 shares of common stock in exchange for an equal number of phantom stock units.</footnote>
        <footnote id="F3">On March 1, 2011, the common stock of Wisconsin Energry Corporation split 2-for-1, resulting in the reporting person's directly held ownership of 7,518.3446 additional shares of common stock.</footnote>
        <footnote id="F4">The 2-for-1 stock split resulted in the reporting person's indirectly held ownership of 3,000 additional shares of common stock.</footnote>
        <footnote id="F5">One-for-one.</footnote>
        <footnote id="F6">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>
        <footnote id="F7">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>
        <footnote id="F8">The 2-for-1 stock split resulted in the reporting person's ownership of 16,467.3509 additional phantom stock units.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>\s\ Joshua M. Erickson, as Attorney-in-Fact</signatureName>
        <signatureDate>2012-01-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0304
4
2012-01-03
0000783325
WISCONSIN ENERGY CORP
WEC
0001196937
BERGSTROM JOHN F
231 WEST MICHIGAN STREET
MILWAUKEE,
WI
53203
1
0
0
0
Common Stock
2012-01-03
4
A
0
2294
0
A
17563.7084
D
Common Stock
2012-01-03
4
D
0
3905.3818
D
13658.3266
D
Common Stock
6000
I
by Trust
Phantom Stock Units
2012-01-03
4
A
0
3905.3818
A
Common Stock
3905.3818
37649.3059
D
Includes shares acquired pursuant to a dividend reinvestment feature of Wisconsin Energy Corporation's Stock Plus Investment Plan in transactions exempt from Section 16 pursuant to Rule 16a-11.
Upon the vesting of restricted stock granted to the reporting person on January 2, 2009, the reporting person deferred the receipt of 3,905.3818 shares of common stock and instead received 3,905.3818 phantom stock units pursuant to the WEC Directors' Deferred Compensation Plan (DDCP).  As a result, the reporting person is reporting the disposition of 3,905.3818 shares of common stock in exchange for an equal number of phantom stock units.
On March 1, 2011, the common stock of Wisconsin Energry Corporation split 2-for-1, resulting in the reporting person's directly held ownership of 7,518.3446 additional shares of common stock.
The 2-for-1 stock split resulted in the reporting person's indirectly held ownership of 3,000 additional shares of common stock.
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.
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.
The 2-for-1 stock split resulted in the reporting person's ownership of 16,467.3509 additional phantom stock units.
\s\ Joshua M. Erickson, as Attorney-in-Fact
2012-01-05