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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-12-15</periodOfReport>

    <issuer>
        <issuerCik>0000007789</issuerCik>
        <issuerName>ASSOCIATED BANC-CORP</issuerName>
        <issuerTradingSymbol>ASBC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001044530</rptOwnerCik>
            <rptOwnerName>KAMERICK EILEEN A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O ASSOCIATED BANC-CORP</rptOwnerStreet1>
            <rptOwnerStreet2>433 MAIN STREET</rptOwnerStreet2>
            <rptOwnerCity>GREEN BAY</rptOwnerCity>
            <rptOwnerState>WI</rptOwnerState>
            <rptOwnerZipCode>54301</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock $0.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2014-12-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>52</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>17.85</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>13909</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Dividend equivalents will become fully vested on the fourth anniversary of the grant of the restricted stock units they have been paid on. They are payable solely in shares of common stock following the date the Insider ceases serving as a director.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Tracy A. Devine, attorney-in-fact for Eileen A. Kamerick</signatureName>
        <signatureDate>2014-12-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
