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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-07-11</periodOfReport>

    <issuer>
        <issuerCik>0001140536</issuerCik>
        <issuerName>WILLIS TOWERS WATSON PLC</issuerName>
        <issuerTradingSymbol>WTW</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001881795</rptOwnerCik>
            <rptOwnerName>Qureshi Imran Ahmed</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WILLIS GROUP LIMITED</rptOwnerStreet1>
            <rptOwnerStreet2>51 LIME STREET</rptOwnerStreet2>
            <rptOwnerCity>LONDON</rptOwnerCity>
            <rptOwnerState>X0</rptOwnerState>
            <rptOwnerZipCode>EC3M 7DQ</rptOwnerZipCode>
            <rptOwnerStateDescription>UNITED KINGDOM</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>Head of North America</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Restricted Share Unit</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2025-07-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>45.1665</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>307.32</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F1"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Ordinary Shares, nominal value $0.000304635 per share</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>45.1665</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2839.0021</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Restricted share units settle for Ordinary Shares, nominal value $0.000304635 per share, on a 1:1 basis 6 months after the reporting person's termination date.</footnote>
        <footnote id="F2">Includes restricted share units acquired pursuant to the Willis Towers Watson Non-Qualified Deferred Savings Plan for U.S. Employees (the &quot;Plan&quot;), including the participant's deferral election under the Plan and the Company's matching contribution on the participant's deferral election credited to the participant's account in the form of restricted share units under the Plan.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Imran Qureshi by Lina Vanessa Jaramillo, Attorney-in-Fact (power of attorney previously filed)</signatureName>
        <signatureDate>2025-07-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
