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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 Fd2Pu/ZUAR2/yJQAQna7kS352XTEtgHMJG0kJU38F8Rj9txi7uOYG5YOmV29IB+n
 mgB4ZAIdW1ttoBDfEHqGBg==

<SEC-DOCUMENT>0000062709-06-000108.txt : 20060517
<SEC-HEADER>0000062709-06-000108.hdr.sgml : 20060517
<ACCEPTANCE-DATETIME>20060517163232
ACCESSION NUMBER:		0000062709-06-000108
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20060516
FILED AS OF DATE:		20060517
DATE AS OF CHANGE:		20060517

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			MARSH & MCLENNAN COMPANIES, INC.
		CENTRAL INDEX KEY:			0000062709
		STANDARD INDUSTRIAL CLASSIFICATION:	INSURANCE AGENTS BROKERS & SERVICES [6411]
		IRS NUMBER:				362668272
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		1166 AVENUE OF THE AMERICAS
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10036
		BUSINESS PHONE:		2123455000

	MAIL ADDRESS:	
		STREET 1:		1166 AVENUE OF THE AMERICAS
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10036

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MARSH & MCLENNAN COMPANIES INC
		DATE OF NAME CHANGE:	19920703

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	MARLENNAN CORP
		DATE OF NAME CHANGE:	19760505

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BAKER  LESLIE M JR
		CENTRAL INDEX KEY:			0001183373

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-05998
		FILM NUMBER:		06849453

	BUSINESS ADDRESS:	
		STREET 1:		C/O AUITY BRANDS INC
		STREET 2:		1170 PEACHTREE STREET NE STE 2400
		CITY:			ATLANTA
		STATE:			GA
		ZIP:			30309
		BUSINESS PHONE:		336-499-7972

	MAIL ADDRESS:	
		STREET 1:		C/O OLD SALEM
		STREET 2:		BOX F, SALEM STATION
		CITY:			WINSTON-SALEM
		STATE:			NC
		ZIP:			27108
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>doc.xml
<DESCRIPTION>PRIMARY DOCUMENT
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-05-16</periodOfReport>

    <issuer>
        <issuerCik>0000062709</issuerCik>
        <issuerName>MARSH &amp; MCLENNAN COMPANIES, INC.</issuerName>
        <issuerTradingSymbol>MMC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001183373</rptOwnerCik>
            <rptOwnerName>BAKER  LESLIE M JR</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O MARSH &amp; MCLENNAN COMPANIES, INC.</rptOwnerStreet1>
            <rptOwnerStreet2>1166 AVENUE OF THE AMERICAS</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2006-05-16</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>3000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.9599</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3000</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes></footnotes>

    <ownerSignature>
        <signatureName>Leon J. Lichter, Attorney-in-Fact</signatureName>
        <signatureDate>2006-05-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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