<?xml version="1.0"?>
<ownershipDocument>
    <schemaVersion>X0101</schemaVersion>

    <documentType>4</documentType>
<periodOfReport>2003-07-15</periodOfReport>
<notSubjectToSection16>0</notSubjectToSection16>
    <issuer>
        <issuerCik>0000831001</issuerCik>
        <issuerName>CITIGROUP INC</issuerName>
        <issuerTradingSymbol>C</issuerTradingSymbol></issuer>
<reportingOwner>
<reportingOwnerId>
            <rptOwnerCik>0001225708</rptOwnerCik>
            <rptOwnerName>WILLUMSTAD ROBERT B</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>  </rptOwnerStreet1>
            <rptOwnerStreet2>  </rptOwnerStreet2>
            <rptOwnerCity>  </rptOwnerCity>
            <rptOwnerState>  </rptOwnerState>
            <rptOwnerZipCode>  </rptOwnerZipCode>
        </reportingOwnerAddress>
            <reportingOwnerRelationship>
<isDirector>1</isDirector>
<isOfficer>1</isOfficer>
<isTenPercentOwner>0</isTenPercentOwner>
<isOther>0</isOther>
<officerTitle>President</officerTitle>
<otherText></otherText></reportingOwnerRelationship></reportingOwner>
<nonDerivativeSecurity>
<securityTitle>
<value>Common Stock</value></securityTitle>
<transactionDate>
<value>2003-07-15</value></transactionDate>
<transactionCoding>
<transactionFormType>4</transactionFormType>
<transactionCode>A</transactionCode>
<equitySwapInvolved>0</equitySwapInvolved></transactionCoding>
<transactionTimeliness>
<value></value></transactionTimeliness>
<transactionAmounts>
<transactionShares>
<value>318337</value>
<footnoteId id="F1"/></transactionShares>
<transactionValue>
<value>0</value></transactionValue>
<transactionAcquiredDisposedCode>
<value>A</value></transactionAcquiredDisposedCode></transactionAmounts>
<postTransactionAmounts>
<sharesOwnedFollowingTransaction>
<value>1472427.5</value>
<footnoteId id="F2"/></sharesOwnedFollowingTransaction></postTransactionAmounts>
<ownershipNature>
<directOrIndirectOwnership>
<value>D</value></directOrIndirectOwnership>
<natureOfOwnership>
<value></value></natureOfOwnership></ownershipNature></nonDerivativeSecurity>
<footnotes>
<footnote id="F1">Award of restricted stock under the Issuer&apos;s 1999 Stock Incentive Plan (&quot;SIP&quot;).</footnote>
<footnote id="F2">Includes 98,681 shares directly beneficially owned by the Reporting Person in his capacity as trustee of two Grantor Retained Annuity Trusts.  In addition, the Reporting Person indirectly beneficially owns 8,594 shares of common stock as of June 30, 2003 under the Issuer&apos;s 401(k) Plan.</footnote></footnotes>
<ownerSignature>
<signatureName>Robert B. Willumstad by Glenn S. Gray, Attorney-in Fact</signatureName>
<signatureDate>2003-07-17</signatureDate></ownerSignature></ownershipDocument>


