<?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>0001344979</rptOwnerCik>
            <rptOwnerName>Feliciani Joseph</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>Principal Accounting Officer</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>1096</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>10055</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <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>1631</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11686</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reflects an award value of $324,680 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) 306 Restricted Stock Units vesting on 1/31/16, (ii) 1,805 Restricted Stock Units vesting on 1/31/16, (iii) 600 Restricted Stock Units vesting in equal installments on 1/31/16 and 1/31/17, (iv) 944 Restricted Stock Units vesting in equal installments on 1/31/16, 1/31/17 and 1/31/18, (v) 1,096 Restricted Stock Units vesting in equal installments on 1/31/17, 1/31/18 and 1/31/19, (vi) 1,316 Restricted Stock Units vesting on 1/31/17 and (vii) 1,404 Restricted Stock units vesting on 1/31/18. Each Restricted Stock Unit is payable solely by delivery of an equal number of shares of Common Stock.</footnote>
        <footnote id="F3">Reflects an award value of $483,000 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 on 1/31/19.</footnote>
        <footnote id="F4">Includes (i) 306 Restricted Stock Units vesting on 1/31/16, (ii) 1,805 Restricted Stock Units vesting on 1/31/16, (iii) 600 Restricted Stock Units vesting in equal installments on 1/31/16 and 1/31/17, (iv) 944 Restricted Stock Units vesting in equal installments on 1/31/16, 1/31/17 and 1/31/18, (v) 1,096 Restricted Stock Units vesting in equal installments on 1/31/17, 1/31/18 and 1/31/19, (vi) 1,316 Restricted Stock Unit is vesting on 1/31/17, (vii) 1,404 Restricted Stock units vesting on 1/31/18 and (viii) 1,631 Restricted Stock Units vesting on 1/31/19. 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 Joseph Feliciani</signatureName>
        <signatureDate>2016-01-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
