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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-06-02</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002067282</rptOwnerCik>
            <rptOwnerName>Manso Julio</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>
            <isOfficer>1</isOfficer>
            <officerTitle>EVP, CHRO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock $0.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2025-06-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>8522</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.47</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8522</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock $0.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2025-06-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F3"/>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4315</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.47</value>
                    <footnoteId id="F4"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12837</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares vest in three equal annual installments on the 1st, 2nd and 3rd anniversary date after hire date.</footnote>
        <footnote id="F2">The number of shares of Common Stock representing the reporting person's Sign-on Grant in connection with the commencement of his employment with Associated Banc-Corp (the &quot;Company&quot;) was determined based on the average of the closing prices of the Company's common stock for the ten trading days preceding his June 2, 2025 starting date, which ranged from $23.00 to $24.28, inclusive.
The reporting person undertakes to provide to Associated Banc-Corp, any security holders of Associated Banc-Corp, or the staff of the Securities and Exchange Commission, upon request, full information regarding the share prices set forth in this footnote.</footnote>
        <footnote id="F3">Represents the 25% Time-Based portion of the LTIPP shares, which will vest in four equal annual installments beginning  February 8, 2026.</footnote>
        <footnote id="F4">Share price was determined based on the average of the closing prices of the Company's common stock for the ten trading days preceding his June 2, 2025 starting date, which ranged from $23.00 to $24.28, inclusive. The reporting person undertakes to provide to Associated Banc-Corp, any security holders of Associated Banc-Corp, or the staff of the Securities and Exchange Commission, upon request, full information regarding the share prices set forth in this footnote.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Lynn M. Floeter, by POA from Julio Manso</signatureName>
        <signatureDate>2025-06-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
