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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2016-01-19</periodOfReport>

    <issuer>
        <issuerCik>0001364742</issuerCik>
        <issuerName>BlackRock Inc.</issuerName>
        <issuerTradingSymbol>BLK</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001572242</rptOwnerCik>
            <rptOwnerName>Shedlin Gary</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>BLACKROCK, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>55 EAST 52ND STREET</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10055</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>CFO &amp; Senior Managing Director</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Shares Of Common Stock (par Value $0.01 Per Share)</value>
            </securityTitle>
            <transactionDate>
                <value>2016-01-19</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>4727</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>29530</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reflects an award value of $1,400,000 converted to a number of Restricted Stock Units by dividing the approved award value by $296.120, which was the average of the high and low price per share of Common Stock on January 19, 2016.  This grant was approved by the Management Development and Compensation Committee on January 13, 2016.  Restricted Stock Units vest in equal installments on 1/31/17, 1/31/18 and 1/31/19.</footnote>
        <footnote id="F2">Includes (i) 2,372 Restricted Stock Units vesting on 1/31/16, (ii) 2,508 Restricted Stock Units vesting in equal installments on 1/31/16 and 1/31/17, (iii) 4,144 Restricted Stock Units vesting in equal installments on 1/31/16, 1/31/17 and 1/31/18, (iv) 4,727 Restricted Stock Units vesting in equal installments on 1/31/17, 1/31/18 and 1/31/19 and (v) 7,680 Restricted Stock Units awarded on 1/17/14 that will vest in whole or in part only on the satisfaction of one or more previously-disclosed Common Stock price targets, but which may not vest before 1/31/18 and will expire on 1/31/20 to the extent not then vested. Each Restricted Stock Unit is payable solely by delivery of an equal number of shares of Common Stock.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Daniel R. Waltcher as Attorney-in-Fact for Gary Shedlin</signatureName>
        <signatureDate>2016-01-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
