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

    <schemaVersion>X0508</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2025-05-21</periodOfReport>

    <issuer>
        <issuerCik>0000097745</issuerCik>
        <issuerName>THERMO FISHER SCIENTIFIC INC.</issuerName>
        <issuerTradingSymbol>TMO</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001010270</rptOwnerCik>
            <rptOwnerName>JOHNSON JENNIFER M</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>168 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>WALTHAM</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02451</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2025-05-21</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>565</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>904</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <remarks>Reporting Person is the President, Chief Executive Officer and a Director of Franklin Resources, Inc., a global investment management organization operating as Franklin Templeton?. Franklin Templeton subsidiaries manage investment products and client accounts that hold equity securities of the Issuer in the ordinary course of business. Reporting Person disclaims beneficial ownership of such securities.</remarks>

    <ownerSignature>
        <signatureName>/s/ Melodie T. Morin, Attorney-in-Fact for Jennifer M. Johnson</signatureName>
        <signatureDate>2025-05-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0508
4
2025-05-21
0000097745
THERMO FISHER SCIENTIFIC INC.
TMO
0001010270
JOHNSON JENNIFER M
168 THIRD AVENUE
WALTHAM
MA
02451
1
0
Common Stock
2025-05-21
4
A
0
565
0
A
904
D
Reporting Person is the President, Chief Executive Officer and a Director of Franklin Resources, Inc., a global investment management organization operating as Franklin Templeton?. Franklin Templeton subsidiaries manage investment products and client accounts that hold equity securities of the Issuer in the ordinary course of business. Reporting Person disclaims beneficial ownership of such securities.
/s/ Melodie T. Morin, Attorney-in-Fact for Jennifer M. Johnson
2025-05-22