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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-07-02</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001094093</issuerCik>
        <issuerName>PROGRESS ENERGY INC</issuerName>
        <issuerTradingSymbol>PGN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001167322</rptOwnerCik>
            <rptOwnerName>PRYOR CHARLES W JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1164 PRYOR RIDGE TRAIL</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>LYNCHBURG</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>24503</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

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                <value>Common Stock</value>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1042</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
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                    <value>D</value>
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            </transactionAmounts>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
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                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
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    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Units based on value of Common Stock</value>
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            </securityTitle>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>4019</value>
                </transactionShares>
                <transactionPricePerShare>
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                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
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                <underlyingSecurityTitle>
                    <value>Common Stock</value>
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                <underlyingSecurityShares>
                    <value>4019</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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            <securityTitle>
                <value>Units based on value of Common Stock</value>
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                <value>2012-07-02</value>
            </transactionDate>
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                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>7725</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F5"/>
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                    <value>D</value>
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                <natureOfOwnership>
                    <value></value>
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        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Disposed of pursuant to the merger (the &quot;Merger&quot;) of Progress Energy, Inc. (&quot;Progress&quot;) with a subsidiary of Duke Energy Corporation (&quot;Duke&quot;) whereby each share of Progress common stock, without par value, was converted into .87083 shares of Duke common stock, par value $.001 per share, having a market value based on the closing price of a share of Duke common stock on the New York Stock Exchange on the last day of trading prior to the effective date of the Merger of $69.84 (as adjusted to reflect Duke's 1-for-3 reverse stock split) per share and a cash payment being made for any fractional shares.</footnote>
        <footnote id="F2">Under the Progress Non-Employee Director Deferred Compensation Plan, non-employee directors of the Progress Board of Directors (the &quot;Board&quot;) could elect to defer a portion of their annual retainer and Board attendance fees until after the termination of their service on the Board. Any deferred fees were deemed to be invested in a number of units of common stock of Progress.</footnote>
        <footnote id="F3">The Progress Non-Employee Director Stock Unit Plan provides for an annual grant of stock units equivalent to $60,000 to each non-employee director. Each unit is equal in economic value to one share of Progress' common stock.</footnote>
        <footnote id="F4">Each Non-Employee Director Deferred Compensation Plan Unit, which was convertible at a rate of 1 unit for 1 share of Progress common stock, without par value, was disposed of pursuant to the Merger in exchange for .87083 corresponding units of Duke; subject to the same terms and conditions.</footnote>
        <footnote id="F5">Each Non-Employee Director Stock Unit, which was convertible at a rate of 1 unit for 1 share of Progress common stock, without par value, was disposed of pursuant to the Merger in exchange for .87083 corresponding units of Duke; subject to the same terms and conditions.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Charles W. Pryor, Jr. by Holly H. Wenger pursuant to POA</signatureName>
        <signatureDate>2012-07-05</signatureDate>
    </ownerSignature>
</ownershipDocument>