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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-10-14</periodOfReport>

    <issuer>
        <issuerCik>0001317630</issuerCik>
        <issuerName>ITC Holdings Corp.</issuerName>
        <issuerTradingSymbol>ITC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001390811</rptOwnerCik>
            <rptOwnerName>Franklin Chris</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>27175 ENERGY WAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NOVI</rptOwnerCity>
            <rptOwnerState>MI</rptOwnerState>
            <rptOwnerZipCode>48377</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock Without Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2016-10-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>5806</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>45.72</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>6549</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock Without Par Value</value>
            </securityTitle>
            <transactionDate>
                <value>2016-10-14</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>6549</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reporting Person held unvested restricted shares granted in 2014, 2015 and 2016 with time-based performance criteria.  Pursuant to the Merger Agreement, these shares became vested at the Effective Time and converted into the right to receive cash.</footnote>
        <footnote id="F2">Pursuant to the Agreement and Plan of Merger among FortisUS Inc., Element Acquisition Sub Inc., Fortis Inc., and ITC Holdings Corp., dated as of February 9, 2016 (the &quot;Merger Agreement&quot;), at the effective time of the merger (the &quot;Effective Time), each outstanding share converted into the right to receive US$22.57 plus .7520 of a share of Fortis Inc. stock, which fractional share had a market value of US$29.84 at the Effective Time.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Christopher H. Franklin</signatureName>
        <signatureDate>2016-10-18</signatureDate>
    </ownerSignature>
</ownershipDocument>
