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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2022-01-18</periodOfReport>

    <dateOfOriginalSubmission>2022-01-20</dateOfOriginalSubmission>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001486267</rptOwnerCik>
            <rptOwnerName>WILSON MARK A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>55 EAST 52ND STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10055</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2022-01-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>288</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>832.07</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2207</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Restricted Stock Units granted to non-employee directors under the Second Amended and Restated BlackRock, Inc. 1999 Stock Award and Incentive Plan (the &quot;Plan&quot;), based on $832.07 per share which was the average of the high and low price per share of Common Stock on January 18, 2022. Restricted Stock Units vest upon the director's election or re-election, as applicable, at the 2022 Annual Meeting of Shareholders and will be settled in shares of Common Stock on the third anniversary of the date of grant, unless the director has elected to receive settlement of such shares on the date that he or she ceases to be a member of the Board (either in a lump sum or in five equal annual installments beginning on such date).</footnote>
        <footnote id="F2">This reflects an adjustment to include an aggregate of 73 shares of Common Stock previously awarded under the Plan and deferred until retirement, which were not reflected in the number of shares as previously reported.  Those awards were inadvertently reported on a net of tax basis and should have been reported on a gross basis.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ R. Andrew Dickson III as Attorney-in-Fact for Mark A. Wilson</signatureName>
        <signatureDate>2022-07-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
