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

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2020-08-16</periodOfReport>

    <noSecuritiesOwned>1</noSecuritiesOwned>

    <issuer>
        <issuerCik>0000007332</issuerCik>
        <issuerName>SOUTHWESTERN ENERGY CO</issuerName>
        <issuerTradingSymbol>SWN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001044584</rptOwnerCik>
            <rptOwnerName>JOHNSON S P IV</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>10000 ENERGY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SPRING</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77391-2359</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <footnotes></footnotes>

    <remarks>No securities beneficially owned.</remarks>

    <ownerSignature>
        <signatureName>/s/ Melissa D. McCarty, Attorney-in-Fact for Mr. Johnson</signatureName>
        <signatureDate>2020-08-25</signatureDate>
    </ownerSignature>
</ownershipDocument>
