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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2018-01-08</periodOfReport>

    <issuer>
        <issuerCik>0001591517</issuerCik>
        <issuerName>Time Inc.</issuerName>
        <issuerTradingSymbol>TIME</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001689488</rptOwnerCik>
            <rptOwnerName>Murray Alan S</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TIME INC.</rptOwnerStreet1>
            <rptOwnerStreet2>225 LIBERTY STREET</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10281</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>Chief Content Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>14.20</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2018-01-08</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>100000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>14.20</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2018-01-31</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-07-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock, par value $0.01</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>100000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>100000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">On July 24, 2017, the reporting person was granted an option to purchase 100,000 shares of common stock.  The number of options eligible to vest was subject to the Company's achievement, by December 31, 2017, of four operational performance goals.  On January 8, 2018, the Company determined that all four operational performance goals were achieved and that, therefore, all 100,000 options were eligible to vest, solely upon continued performance of service, in equal installments on the first and second anniversaries of the grant date.  However, these options became exercisable in full, on an accelerated basis, on January 31, 2018, by reason of the merger of the Company with a wholly-owned subsidiary of Meredith Corporation.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Monika Roth, Attorney-in-Fact for Alan S. Murray</signatureName>
        <signatureDate>2018-02-02</signatureDate>
    </ownerSignature>
</ownershipDocument>
