<SEC-DOCUMENT>0001127602-20-028103.txt : 20201104
<SEC-HEADER>0001127602-20-028103.hdr.sgml : 20201104
<ACCEPTANCE-DATETIME>20201104160122
ACCESSION NUMBER:		0001127602-20-028103
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20201102
FILED AS OF DATE:		20201104
DATE AS OF CHANGE:		20201104

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Beshar Peter J
		CENTRAL INDEX KEY:			0001309593

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-05998
		FILM NUMBER:		201286563

	MAIL ADDRESS:	
		STREET 1:		C/O MARSH & MCLENNAN COMPANIES, INC.
		STREET 2:		1166 AVENUE OF THE AMERICAS
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10036

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
</SEC-HEADER>
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<SEQUENCE>1
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<DESCRIPTION>PRIMARY DOCUMENT
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    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2020-11-02</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001309593</rptOwnerCik>
            <rptOwnerName>Beshar Peter J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1166 AVENUE OF THE AMERICAS</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10036</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isOfficer>1</isOfficer>
            <officerTitle>EVP and General Counsel</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
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                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2020-08-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
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            <transactionAmounts>
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            <transactionTimeliness></transactionTimeliness>
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                <transactionShares>
                    <value>82275</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>105.20</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
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            <transactionDate>
                <value>2020-11-02</value>
            </transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>75931</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>105.21</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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                <sharesOwnedFollowingTransaction>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>F</transactionCode>
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                <transactionShares>
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                    <value>105.44</value>
                </transactionPricePerShare>
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        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Options (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>48.00</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-11-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness></transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>113872</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <value>2024-02-23</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>113872</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
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        </derivativeTransaction>
        <derivativeTransaction>
            <securityTitle>
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            </securityTitle>
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                <value>56.84</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2020-11-02</value>
            </transactionDate>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionTimeliness></transactionTimeliness>
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                <transactionShares>
                    <value>99207</value>
                </transactionShares>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
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            <exerciseDate>
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            <expirationDate>
                <value>2025-02-22</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>99207</value>
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                </transactionShares>
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                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
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            <exerciseDate>
                <footnoteId id="F4"/>
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            <expirationDate>
                <value>2026-02-21</value>
            </expirationDate>
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                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>97319</value>
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    <footnotes>
        <footnote id="F1">On November 2, 2020 Mr. Beshar exercised 113,872 options that were granted to him in 2014, 99,207 options that were granted to him in 2015 and 97,319 options that were granted to him in 2016 and thereby increased his net ownership of MMC common stock by 77,536 from 468,844 to 546,380 shares. 82,275 shares were used to satisfy the exercise price and applicable taxes for the options granted in 2014, 75,931 shares were used to satisfy the exercise price and applicable taxes for the options granted in 2015 and 74,656 shares were used to satisfy the exercise price and applicable taxes on the options granted in 2016 in exempt transactions.</footnote>
        <footnote id="F2">These options were granted on February 24, 2014 and vested in four equal annual installments on February 24th of 2015, 2016, 2017 and 2018.</footnote>
        <footnote id="F3">These options were granted on February 23, 2015 and vested in four equal annual installments on February 23rd of 2016, 2017, 2018 and 2019.</footnote>
        <footnote id="F4">These options were granted on February 22, 2016 and vested in four equal annual installments on February 22nd of 2017, 2018, 2019 and 2020.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Tiffany D. Wooley, Attorney-in-Fact</signatureName>
        <signatureDate>2020-11-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
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</TEXT>
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</SEC-DOCUMENT>
