<SEC-DOCUMENT>0001002910-20-000021.txt : 20200103
<SEC-HEADER>0001002910-20-000021.hdr.sgml : 20200103
<ACCEPTANCE-DATETIME>20200103180332
ACCESSION NUMBER:		0001002910-20-000021
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20200101
FILED AS OF DATE:		20200103
DATE AS OF CHANGE:		20200103

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			MARK RICHARD J
		CENTRAL INDEX KEY:			0001190100

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14756
		FILM NUMBER:		20507219

	MAIL ADDRESS:	
		STREET 1:		1901 CHOUTEAU AVENUE MC-1310
		CITY:			ST. LOUIS
		STATE:			MO
		ZIP:			63103

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			AMEREN CORP
		CENTRAL INDEX KEY:			0001002910
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRIC & OTHER SERVICES COMBINED [4931]
		IRS NUMBER:				431723446
		STATE OF INCORPORATION:			MO
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1901 CHOUTEAU AVE
		STREET 2:		MC 1370
		CITY:			ST LOUIS
		STATE:			MO
		ZIP:			63166-6149
		BUSINESS PHONE:		314-621-3222

	MAIL ADDRESS:	
		STREET 1:		1901 CHOUTEAU AVE
		STREET 2:		MC 1370
		CITY:			ST LOUIS
		STATE:			MO
		ZIP:			63103
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>wf-form4_157809259529118.xml
<DESCRIPTION>FORM 4
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-01-01</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001002910</issuerCik>
        <issuerName>AMEREN CORP</issuerName>
        <issuerTradingSymbol>AEE</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001190100</rptOwnerCik>
            <rptOwnerName>MARK RICHARD J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>P.O. BOX 66149</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ST. LOUIS</rptOwnerCity>
            <rptOwnerState>MO</rptOwnerState>
            <rptOwnerZipCode>63166-6149</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Chmn &amp; President of Subsidiary</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, $.01 Par Value</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12172</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By 401(K)</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, $.01 Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2020-01-01</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>3763</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>133515</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents the estimated number of share equivalents held by the reporting person in the unitized stock fund included in the Ameren Corporation Savings Investment Plan as of December 31, 2019.</footnote>
        <footnote id="F2">These restricted stock units were granted under the issuer's 2014 Omnibus Incentive Compensation Plan (the &quot;Plan&quot;) and are scheduled to vest upon the payment date in 2023, which shall be no later than March 15, 2023, subject to the terms of the Plan and the applicable award agreement issued thereunder.</footnote>
        <footnote id="F3">Amount includes 2,694 shares acquired during 2019 through monthly payroll deductions and reinvested dividends, as well as 1,189 accrued dividend equivalents acquired during 2018 and 2019 pursuant to a dividend reinvestment feature of restricted stock units granted under the issuer's 2014 Omnibus Incentive Compensation Plan.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Jonathan T. Shade, Asst. Secy. of Ameren Corporation, attorney-in-fact for Richard J. Mark</signatureName>
        <signatureDate>2020-01-03</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
