Marsh & McLennan Companies (MMC) 10-Q 17 Oct 24 2024 Q3 Quarterly report Financial data

COVER PAGE

COVER PAGE - shares	9 Months Ended
	Sep. 30, 2024	Oct. 14, 2024
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2024
Document Transition Report	false
Entity Registrant Name	Marsh & McLennan Companies, Inc.
Entity Address, Address Line One	1166 Avenue of the Americas
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10036
City Area Code	212
Local Phone Number	345-5000
Entity File Number	1-5998
Entity Address, State or Province	DE
Entity Tax Identification Number	36-2668272
Title of 12(b) Security	Common Stock, par value $1.00 per share
Trading Symbol	MMC
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		491,121,531
Entity Central Index Key	0000062709
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	Q3
Amendment Flag	false
New York Stock Exchange
Entity Information [Line Items]
Security Exchange Name	NYSE
Chicago Stock Exchange
Entity Information [Line Items]
Security Exchange Name	CHX

CONSOLIDATED STATEMENTS OF INCO

CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Income Statement [Abstract]
Revenue	$ 5,697	$ 5,382	$ 18,391	$ 17,182
Expense:
Compensation and benefits	3,442	3,287	10,366	9,831
Other operating expenses	1,147	1,099	3,350	3,172
Operating expenses	4,589	4,386	13,716	13,003
Operating income	1,108	996	4,675	4,179
Other net benefit credits	68	62	201	180
Interest income	12	16	61	40
Interest expense	(154)	(145)	(469)	(427)
Investment income	1	1	3	6
Income before income taxes	1,035	930	4,471	3,978
Income tax expense	283	192	1,155	941
Net income before non-controlling interests	752	738	3,316	3,037
Less: Net income attributable to non-controlling interests	5	8	44	37
Net income attributable to the Company	$ 747	$ 730	$ 3,272	$ 3,000
Net income per share attributable to the Company:
Basic (in dollars per share)	$ 1.52	$ 1.48	$ 6.65	$ 6.07
Diluted (in dollars per share)	$ 1.51	$ 1.47	$ 6.59	$ 6.01
Average number of shares outstanding:
Basic (in shares)	492	494	492	494
Diluted (in shares)	496	499	496	499
Shares outstanding (in shares)	491	493	491	493

CONSOLIDATED STATEMENTS OF COMP

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net income before non-controlling interests	$ 752	$ 738	$ 3,316	$ 3,037
Other comprehensive income (loss), before tax:
Foreign currency translation adjustments	661	(473)	389	(131)
(Loss) gain related to pension/post-retirement plans	(173)	107	(105)	(13)
Other comprehensive income (loss) before tax	488	(366)	284	(144)
Income tax (benefit) expense on other comprehensive loss	(49)	39	(21)	2
Other comprehensive income (loss), net of tax	537	(405)	305	(146)
Comprehensive income	1,289	333	3,621	2,891
Less: comprehensive income attributable to non-controlling interest	5	8	44	37
Comprehensive income attributable to the Company	$ 1,284	$ 325	$ 3,577	$ 2,854

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Current assets:
Cash and cash equivalents	$ 1,798	$ 3,358
Cash and cash equivalents held in a fiduciary capacity	11,923	10,794
Receivables
Commissions and fees	6,783	5,806
Advanced premiums and claims	102	103
Other	702	660
Gross receivables	7,587	6,569
Less-allowance for credit losses	(165)	(151)
Net receivables	7,422	6,418
Other current assets	1,143	1,178
Total current assets	22,286	21,748
Goodwill	18,235	17,231
Other intangible assets	2,720	2,630
Fixed assets (net of accumulated depreciation and amortization of $1,638 at September 30, 2024 and $1,562 at December 31, 2023)	884	882
Pension related assets	2,384	2,051
Right of use assets	1,487	1,541
Deferred tax assets	242	357
Other assets	1,626	1,590
Total assets	49,864	48,030
Current liabilities:
Short-term debt	518	1,619
Accounts payable and accrued liabilities	3,099	3,403
Accrued compensation and employee benefits	2,785	3,346
Current lease liabilities	313	312
Accrued income taxes	565	321
Dividends payable	401	0
Fiduciary liabilities	11,923	10,794
Total current liabilities	19,604	19,795
Long-term debt	12,330	11,844
Pension, post-retirement and post-employment benefits	704	779
Long-term lease liabilities	1,618	1,661
Liabilities for errors and omissions	330	314
Other liabilities	1,396	1,267
Commitments and contingencies	0	0
Equity:
Preferred stock, $1 par value, authorized 6,000,000 shares, none issued	0	0
Common stock, $1 par value, authorized 1,600,000,000 shares, issued 560,641,640 shares at September 30, 2024 and December 31, 2023	561	561
Additional paid-in capital	1,289	1,242
Retained earnings	24,520	22,759
Accumulated other comprehensive loss	(4,990)	(5,295)
Non-controlling interests	194	179
Stockholders' equity before treasury stock	21,574	19,446
Less – treasury shares, at cost, 69,608,340 shares at September 30, 2024 and 68,635,498 shares at December 31, 2023	(7,692)	(7,076)
Total equity	13,882	12,370
Total liabilities and stockholders' equity	$ 49,864	$ 48,030

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Fixed assets, accumulated depreciation and amortization	$ 1,638	$ 1,562
Preferred stock, par value (in dollars per share)	$ 1	$ 1
Preferred stock, shares authorized (in shares)	6,000,000	6,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$ 1	$ 1
Common stock, shares authorized (in shares)	1,600,000,000	1,600,000,000
Common stock, shares issued (in shares)	560,641,640	560,641,640
Treasury stock, shares (in shares)	69,608,340	68,635,498

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Operating cash flows:
Net income before non-controlling interests	$ 3,316	$ 3,037
Adjustments to reconcile net income provided by operations:
Depreciation and amortization of fixed assets and capitalized software	276	270
Amortization of intangible assets	269	257
Non-cash lease expense	206	215
Adjustments and payments related to contingent consideration assets and liabilities	(69)	(19)
Net gain on investments	0	(6)
Net (gain) loss on disposition of assets	(18)	18
Share-based compensation expense	283	273
Changes in assets and liabilities:
Net receivables	(821)	(670)
Other assets	(45)	(98)
Accrued compensation and employee benefits	(582)	(458)
Provision for taxes, net of payments and refunds	233	242
Contributions to pension and other benefit plans in excess of current year credit	(262)	(246)
Other liabilities	(211)	(103)
Operating lease liabilities	(229)	(237)
Net cash provided by operations	2,346	2,475
Financing cash flows:
Purchase of treasury shares	(900)	(900)
Issuance of commercial paper with maturity greater than 90 days	0	146
Repayment of commercial paper with maturity greater than 90 days	0	(146)
Proceeds from issuance of debt	988	2,170
Repayments of debt	(1,613)	(12)
Payment of bridge loan commitment fees	(23)	0
Purchase of non-controlling interests	(5)	(139)
Shares withheld for taxes on vested units – treasury shares	(177)	(145)
Issuance of common stock from treasury shares	221	165
Payments of deferred and contingent consideration for acquisitions	(91)	(187)
Receipts of deferred and contingent consideration for dispositions	3	2
Distributions of non-controlling interests	(29)	(18)
Dividends paid	(1,110)	(944)
Change in fiduciary liabilities	916	1,223
Net cash (used for) provided by financing activities	(1,820)	1,215
Investing cash flows:
Capital expenditures	(240)	(296)
Purchases of long term investments	(18)	(44)
Sales of long term investments	17	18
Dispositions	106	(18)
Acquisitions, net of cash and cash held in a fiduciary capacity acquired	(1,042)	(619)
Other, net	1	16
Net cash used for investing activities	(1,176)	(943)
Effect of exchange rate changes on cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity	219	(120)
(Decrease)/increase in cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity	(431)	2,627
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at beginning of period	14,152	12,102
Cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity at end of period	13,721	14,729
Cash and cash equivalents	1,798	2,901
Cash and cash equivalents held in a fiduciary capacity	11,923	11,828
Total cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity	$ 13,721	$ 14,729

CONSOLIDATED STATEMENTS OF EQUI

CONSOLIDATED STATEMENTS OF EQUITY - USD ($) $ in Millions	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE LOSS	TREASURY SHARES	NON-CONTROLLING INTERESTS
Balance, beginning of period at Dec. 31, 2022		$ 561	$ 1,179	$ 20,301	$ (5,314)	$ (6,207)	$ 229
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(27)
Issuance of shares under stock compensation plans and employee stock purchase plans			68			255
Purchase of non-controlling interest			(70)
Net income	$ 3,037			3,000			37
Dividend equivalents declared				(9)
Dividends declared				(1,285)
Other comprehensive income (loss), net of tax	(146)				(146)
Purchase of treasury shares	(900)					(900)
Net non-controlling interests acquired							(69)
Distributions and other changes							(17)
Balance, end of period at Sep. 30, 2023	$ 11,586		1,150	22,007	(5,460)	(6,852)	180
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 2.60
Balance, beginning of period at Jun. 30, 2023		561	1,074	21,980	(5,055)	(6,599)	178
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			74
Issuance of shares under stock compensation plans and employee stock purchase plans			2			47
Purchase of non-controlling interest			0
Net income	$ 738			730			8
Dividend equivalents declared				(1)
Dividends declared				(702)
Other comprehensive income (loss), net of tax	(405)				(405)
Purchase of treasury shares						(300)
Net non-controlling interests acquired							0
Distributions and other changes							(6)
Balance, end of period at Sep. 30, 2023	$ 11,586		1,150	22,007	(5,460)	(6,852)	180
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 1.42
Balance, beginning of period at Dec. 31, 2023	$ 12,370	561	1,242	22,759	(5,295)	(7,076)	179
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(41)
Issuance of shares under stock compensation plans and employee stock purchase plans			88			284
Purchase of non-controlling interest			0
Net income	3,316			3,272			44
Dividend equivalents declared				(10)
Dividends declared				(1,501)
Other comprehensive income (loss), net of tax	305				305
Purchase of treasury shares	(900)					(900)
Net non-controlling interests acquired							0
Distributions and other changes							(29)
Balance, end of period at Sep. 30, 2024	$ 13,882		1,289	24,520	(4,990)	(7,692)	194
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 3.05
Balance, beginning of period at Jun. 30, 2024		$ 561	1,197	24,578	(5,527)	(7,442)	198
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			84
Issuance of shares under stock compensation plans and employee stock purchase plans			8			50
Purchase of non-controlling interest			0
Net income	$ 752			747			5
Dividend equivalents declared				(3)
Dividends declared				(802)
Other comprehensive income (loss), net of tax	537				537
Purchase of treasury shares						(300)
Net non-controlling interests acquired							0
Distributions and other changes							(9)
Balance, end of period at Sep. 30, 2024	$ 13,882		$ 1,289	$ 24,520	$ (4,990)	$ (7,692)	$ 194
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 1.63

Nature of Operations

Nature of Operations	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations Marsh & McLennan Companies, Inc., and its consolidated subsidiaries (the "Company"), a global professional services firm, is organized based on the different services that it offers. Under this structure, the Company’s two business segments are Risk and Insurance Services and Consulting. The Risk and Insurance Services segment ("RIS") includes risk management activities (risk advice, risk transfer, and risk control and mitigation solutions) as well as insurance and reinsurance broking and services for businesses, public entities, insurance companies, associations, professional services organizations, and private clients. The Company conducts business in this segment through Marsh and Guy Carpenter. Marsh provides data-driven risk advisory services and insurance solutions to commercial and consumer clients. Guy Carpenter develops advanced risk, reinsurance and capital strategies that help clients grow profitably and pursue emerging opportunities. The Consulting segment includes health, wealth and career advice, solutions and products, and specialized management, strategic, economic and brand consulting services. The Company conducts business in this segment through Mercer and Oliver Wyman Group. Mercer delivers advice and technology-driven solutions that help organizations redefine the future of work, reshape retirement and investment outcomes, and unlock health and well-being for a changing workforce. Oliver Wyman Group serves as a critical strategic, economic and brand advisor to private sector and governmental clients.

Principles of Consolidation and

Principles of Consolidation and Other Matters	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation and Other Matters	Principles of Consolidation and Other Matters The Company prepared the consolidated financial statements included herein pursuant to the rules and regulations of the Securities and Exchange Commission. For interim filings, certain information and disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States of America (U.S.) have been omitted pursuant to such rules and regulations. The Company believes that the information and disclosures presented are adequate to make such information and disclosures not misleading. These consolidated financial statements should be read in conjunction with the consolidated financial statements and the notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2023 (the "2023 Form 10-K"). The accompanied consolidated financial statements include all wholly-owned and majority-owned subsidiaries. All significant inter-company transactions and balances have been eliminated. The financial information contained herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the Company’s consolidated financial statements as of and for the nine months ended September 30, 2024 and 2023. The preparation of the consolidated financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosures of assets and liabilities at the date of the financial statements, and the reported amounts of revenue and expense during the reporting period. On an ongoing basis, the Company evaluates its estimates, judgments and methodologies. The estimates are based on historical experience and on various other assumptions that the Company believes are reasonable. Such matters include: • estimates of revenue; • impairment assessments and charges; • recoverability of long-lived assets; • liabilities for errors and omissions; • deferred tax assets, uncertain tax positions and income tax expense; • share-based and incentive compensation expense; • the allowance for current expected credit losses on receivables; • useful lives assigned to long-lived assets, and depreciation and amortization; and • fair value estimates of contingent consideration receivable or payable related to acquisitions or dispositions. The Company believes these estimates are reasonable based on information currently available at the time they are made. The Company also considered the potential impact of macroeconomic factors including from the multiple major wars, escalating conflict throughout the Middle East and rising tension in the South China Sea, slower GDP growth or recession, lower interest rates, capital markets volatility, inflation and changes in insurance premium rates to its customer base in various industries and geographies. Insurance exposures subject to variable factors are subject to mid-term and end-of-term adjustments, as well as policy audits, which may reduce premiums and corresponding commissions. Estimates were updated based on internal and industry specific economic data. Actual results may differ from these estimates. Cash and Cash Equivalents Cash and cash equivalents primarily consist of certificates of deposit and time deposits, with original maturities of three months or less, and money market funds. The estimated fair value of the Company's cash and cash equivalents approximates their carrying value. The Company is required to maintain operating funds primarily related to regulatory requirements outside of the U.S. or as collateral under captive insurance arrangements. At September 30, 2024, the Company maintained $507 million compared to $486 million at December 31, 2023 related to these regulatory requirements. Allowance for Credit Losses on Accounts Receivable The Company’s policy for providing an allowance for credit losses on its accounts receivable is based on a combination of factors, including historical write-offs, aging of balances, and other qualitative and quantitative analyses. The charge related to expected credit losses was not material to the consolidated statements of income for the three and nine months ended September 30, 2024 and 2023, respectively. Investments The caption "Investment income" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds. The Company holds investments in certain private equity funds. Investments in private equity funds are accounted for in accordance with the equity method of accounting using a consistently applied three-month lag period adjusted for any known significant changes from the lag period to the reporting date of the Company. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. Investment gains or losses for its proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for in accordance with the equity method of accounting are included in other assets in the consolidated balance sheets. The Company recorded net investment income of $1 million and $3 million for the three and nine months ended September 30, 2024, respectively, compared to net investment income of $1 million and $6 million, respectively, for the corresponding periods in the prior year. Income Taxes The Company's effective tax rate for the three months ended September 30, 2024 was 27.3%, compared with 20.6% for the corresponding quarter of 2023. The effective tax rates for the nine months ended September 30, 2024 and 2023 were 25.8% and 23.7%, respectively. The tax rate in each period reflects the impact of discrete tax items such as excess tax benefits related to share-based compensation, enacted tax legislation, changes in uncertain tax positions, deferred tax adjustments, non-taxable adjustments related to contingent consideration for acquisitions, and valuation allowances for certain tax credits and attributes. The rate for the three and nine months ended September 30, 2024 reflects the previously enacted change in the United Kingdom (U.K.) corporate income tax rate from 19% to 25%, which was effective April 1, 2023. The blended U.K. statutory tax rate for 2023 was 23.5%. The excess tax benefit related to share-based payments is the most significant discrete item for the nine months ended September 30, 2024 and 2023, reducing the effective tax rate by 1.3% and 1.2%, respectively. The reduction to the effective tax rate for the three months ended September 30, 2024 and 2023 is 0.3% and 1.0%, respectively. During the third quarter of 2023, the Company released a valuation allowance related to the realizability of deferred tax assets for its non-U.S. operations of $48 million as a discrete tax benefit, primarily due to the sustained profitability of its operations. This was the most significant discrete item for the three months ended September 30, 2023, reducing the effective tax rate by 4.8%. For the nine months ended September 30, 2023, the reduction to the effective tax rate was 1.1%. The Company's tax rate reflects its income, statutory tax rates, and tax planning in the various jurisdictions in which it operates. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions. Losses in one jurisdiction, generally, cannot offset earnings in another, and within certain jurisdictions profits and losses may not offset between entities. Consequently, losses in certain jurisdictions may require valuation allowances affecting the effective tax rate, depending on estimates of the realizability of associated deferred tax assets. The tax rate is also sensitive to changes in unrecognized tax benefits, including the impact of settled tax audits and expired statutes of limitations. The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in tax returns. The Company's gross unrecognized tax benefits were $122 million at September 30, 2024, and $124 million at December 31, 2023. It is reasonably possible that the total amount of unrecognized tax benefits could decrease up to approximately $66 million within the next twelve months due to settlement of audits and expirations of statutes of limitations. In the third quarter of 2024, the Company received closure notices and assessments from the U.K. tax authority in relation to its 2016-2020 examinations which disallowed certain interest expense deductions. The Company has appealed the assessments and resolving this matter through litigation or alternative dispute resolution may take several years. The Company believes the resolution of tax matters will not have a material effect on the consolidated financial position of the Company. However, an adverse resolution of tax matters could have a material impact on the Company's net income or cash flows and on its effective tax rate in a particular future period. Changes in tax laws, rulings, policies, or related legal and regulatory interpretations occur frequently and may have significant favorable or adverse impacts on our effective tax rate. In 2021, the Organization for Economic Cooperation and Development ("OECD") released model rules for a 15% global minimum tax, known as Pillar Two. Pillar Two has now been enacted by most key non-U.S. jurisdictions where the Company operates, including the U.K. and Ireland. This minimum tax is treated as a period cost beginning in 2024 and does not have a material impact on the Company's financial results of operations for the current period. The Company is monitoring legislative developments, as well as additional guidance from countries that have enacted legislation. We anticipate further legislative activity and administrative guidance in 2024. Restructuring Costs Charges associated with restructuring activities are recognized in accordance with applicable accounting guidance which includes accounting for disposal or exit activities, guidance related to impairment of right-of-use ("ROU") assets related to real estate leases, as well as other costs resulting from accelerated depreciation or amortization of leasehold improvements and other property and equipment. Severance and related costs are recognized based on amounts due under established severance plans or estimates of one-time benefits that will be provided. Typically, severance benefits are recognized when the impacted colleagues are notified of their expected termination and such termination is expected to occur within the legally required notification period. These costs are included in compensation and benefits in the consolidated statements of income. Costs for real estate consolidation are recognized based on the type of cost, and the expected future use of the facility. For locations where the Company does not expect to sub-lease the property, the amortization of any ROU asset is accelerated from the decision date to the cease use date. For locations where the Company expects to sub-lease the properties subsequent to its vacating the property, the ROU asset is reviewed for potential impairment at the earlier of the cease use date or the date a sub-lease is signed. To determine the amount of impairment, the fair value of the ROU asset is determined based on the present value of the estimated net cash flows related to the property. Contractual costs outside of the ROU asset are recognized based on the net present value of expected future cash outflows for which the Company will not receive any benefit. Such amounts are reliant on estimates of future sub-lease income to be received and future contractual costs to be incurred. These costs are included in other operating expenses in the consolidated statements of income. Other costs related to restructuring, such as moving, legal or consulting costs are recognized as incurred. These costs are included in other operating expenses in the consolidated statements of income. Foreign Currency

Revenue

Revenue	9 Months Ended
	Sep. 30, 2024
Revenue from Contract with Customer [Abstract]
Revenue	Revenue The core principle of the revenue recognition guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, the entity applies the following steps: identify the contract(s) with the customer, identify the performance obligations in the contract(s), determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. In accordance with the accounting guidance, a performance obligation is satisfied either at a "point in time" or "over time", depending on the nature of the product or service provided, and the specific terms of the contract with customers. Other revenue included in the consolidated statements of income that is not from contracts with customers is less than 1% of total revenue and is not presented as a separate line item. The Company's revenue policies are provided in more detail in Note 2, Revenue, in the 2023 Form 10-K. The following table disaggregates various components of the Company's revenue: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Marsh: EMEA $ 747 $ 692 $ 2,684 $ 2,482 Asia Pacific 342 311 1,069 980 Latin America 134 134 396 386 Total International 1,223 1,137 4,149 3,848 U.S./Canada 1,711 1,563 5,053 4,634 Total Marsh 2,934 2,700 9,202 8,482 Guy Carpenter 381 359 2,161 2,006 Subtotal 3,315 3,059 11,363 10,488 Fiduciary interest income 138 131 385 330 Total Risk and Insurance Services $ 3,453 $ 3,190 $ 11,748 $ 10,818 Mercer: Wealth $ 625 $ 635 $ 1,909 $ 1,853 Health 520 496 1,605 1,559 Career 307 294 742 731 Total Mercer 1,452 1,425 4,256 4,143 Oliver Wyman Group 810 781 2,436 2,266 Total Consulting $ 2,262 $ 2,206 $ 6,692 $ 6,409 The following table provides contract assets and contract liabilities information from contracts with customers: (In millions) September 30, 2024 December 31, 2023 Contract assets $ 433 $ 357 Contract liabilities $ 864 $ 869 The Company records accounts receivable when the right to consideration is unconditional, subject only to the passage of time. Contract assets primarily relate to quota share reinsurance brokerage and contingent insurer revenue. The Company does not have the right to bill and collect revenue for quota share brokerage until the underlying policies written by the ceding insurer attach to the treaty. Estimated revenue related to the achievement of volume or loss ratio metrics cannot be billed or collected until all related policy placements are completed and the contingency is resolved. Contract assets are included in other current assets in the Company's consolidated balance sheets. Contract liabilities primarily relate to the advance consideration received from customers. Contract liabilities are included in current liabilities in the Company's consolidated balance sheets. Revenue recognized for the three and nine months ended September 30, 2024 that was included in the contract liability balance at the beginning of each of those periods was $149 million and $730 million, respectively, compared to revenue recognized of $187 million and $698 million, respectively, for the corresponding periods in the prior year. The amount of revenue recognized for the three and nine months ended September 30, 2024 from performance obligations satisfied in previous periods, mainly due to variable consideration from contracts with insurers, quota share business and consulting contracts previously considered constrained was $18 million and $61 million, respectively, and $20 million and $64 million, respectively, for the corresponding periods in the prior year. The Company applies the practical expedient and does not disclose the value of unsatisfied performance obligations for (1) contracts with original contract terms of one year or less and (2) contracts where the Company has the right to invoice for services performed.

Fiduciary Assets and Liabilitie

Fiduciary Assets and Liabilities	9 Months Ended
	Sep. 30, 2024
Fiduciary Assets And Liabilities [Abstract]
Fiduciary Assets and Liabilities	Fiduciary Assets and Liabilities The Company, in its capacity as an insurance broker or agent, generally collects premiums from insureds and after deducting its commissions, remits the premiums to the respective insurance underwriters. The Company also collects claims or refunds from underwriters on behalf of insureds. Unremitted insurance premiums and claims proceeds are held by the Company in a fiduciary capacity. The Company's fiduciary assets primarily include bank or short-term time deposits and liquid money market funds, classified as cash and cash equivalents. Since cash and cash equivalents held in a fiduciary capacity are not available for corporate use, they are shown separately in the consolidated balance sheets as cash and cash equivalents held in a fiduciary capacity, with a corresponding amount in current liabilities. Risk and Insurance Services revenue includes interest on fiduciary assets of $138 million and $385 million for the three and nine months ended September 30, 2024 , respectively, and $131 million and $330 million for the three and nine months ended September 30, 2023 , respectively.

Per Share Data

Per Share Data	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Per Share Data	Per Share Data Basic net income per share attributable to the Company is calculated by dividing the after-tax income attributable to the Company by the weighted average number of outstanding shares of the Company’s common stock. Diluted net income per share attributable to the Company is calculated by dividing the after-tax income attributable to the Company by the weighted average number of outstanding shares of the Company’s common stock, which have been adjusted for the dilutive effect of potentially issuable common shares. Basic and Diluted EPS Calculation Three Months Ended Nine Months Ended (In millions, except per share data) 2024 2023 2024 2023 Net income before non-controlling interests $ 752 $ 738 $ 3,316 $ 3,037 Less: Net income attributable to non-controlling interests 5 8 44 37 Net income attributable to the Company $ 747 $ 730 $ 3,272 $ 3,000 Basic weighted average common shares outstanding 492 494 492 494 Dilutive effect of potentially issuable common shares 4 5 4 5 Diluted weighted average common shares outstanding 496 499 496 499 Average stock price used to calculate common stock equivalents $ 222.13 $ 191.66 $ 209.06 $ 178.64

Supplemental Disclosures to the

Supplemental Disclosures to the Consolidated Statements of Cash Flows	9 Months Ended
	Sep. 30, 2024
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosures to the Consolidated Statements of Cash Flows	Supplemental Disclosures to the Consolidated Statements of Cash Flows The following table provides additional information concerning acquisitions, interest and income taxes paid for the nine months ended September 30, 2024 and 2023: (In millions) 2024 2023 Assets acquired, excluding cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity $ 1,310 $ 760 Fiduciary liabilities assumed (8) (14) Liabilities assumed (84) (98) Contingent/deferred purchase consideration (176) (29) Net cash outflow for acquisitions $ 1,042 $ 619 (In millions) 2024 2023 Interest paid $ 538 $ 427 Income taxes paid, net of refunds $ 922 $ 699 The classification of contingent consideration in the consolidated statements of cash flows is dependent upon whether the receipt or payment was part of the initial liability established on the acquisition date (financing) or an adjustment to the acquisition date liability (operating). The following amounts are included in the consolidated statements of cash flows as operating and financing activities: For the Nine Months Ended September 30, (In millions) 2024 2023 Operating: Contingent consideration payments for prior year acquisitions $ (90) $ (41) Receipt of contingent consideration for dispositions — 1 Acquisition/disposition related net charges for adjustments 21 21 Adjustments and payments related to contingent consideration $ (69) $ (19) Financing: Contingent consideration for prior year acquisitions $ (73) $ (135) Deferred consideration related to prior year acquisitions (18) (52) Payments of deferred and contingent consideration for acquisitions $ (91) $ (187) Receipts of contingent consideration for dispositions $ 1 $ 2 The Company had non-cash issuances of common stock in accordance with its share-based payment plan of $328 million and $304 million for the nine months ended September 30, 2024 and 2023, respectively. The Company recorded share-based compensation expense related to restricted stock units, performance stock units and stock options of $90 million and $283 million for the three and nine months ended September 30, 2024, respectively, and $82 million and $273 million for the three and nine months ended September 30, 2023, respectively.

Other Comprehensive (Loss) Inco

Other Comprehensive (Loss) Income	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Other Comprehensive (Loss) Income	Other Comprehensive (Loss) Income The changes, net of tax, in the balances of each component of AOCI for the three and nine months ended September 30, 2024 and 2023, including amounts reclassified out of AOCI, are as follows: (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at July 1, 2024 $ (3,050) $ (2,477) $ (5,527) Other comprehensive (loss) income before reclassifications (135) 668 533 Amounts reclassified from accumulated other comprehensive income 4 — 4 Net current period other comprehensive (loss) income (131) 668 537 Balance at September 30, 2024 (a) $ (3,181) $ (1,809) $ (4,990) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at July 1, 2023 $ (2,811) $ (2,244) $ (5,055) Other comprehensive income (loss) before reclassifications 76 (485) (409) Amounts reclassified from accumulated other comprehensive income 4 — 4 Net current period other comprehensive income (loss) 80 (485) (405) Balance at September 30, 2023 (a) $ (2,731) $ (2,729) $ (5,460) (a) At September 30, 2024 and 2023, balances are net of deferred tax assets in pension and post-retirement plans gains (losses) of $1.5 billion and $1.3 billion, respectively. (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at January 1, 2024 $ (3,101) $ (2,194) $ (5,295) Other comprehensive (loss) income before reclassifications (93) 385 292 Amounts reclassified from accumulated other comprehensive income 13 — 13 Net current period other comprehensive (loss) income (80) 385 305 Balance at September 30, 2024 (a) $ (3,181) $ (1,809) $ (4,990) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at January 1, 2023 $ (2,721) $ (2,593) $ (5,314) Other comprehensive (loss) income before reclassifications (20) (136) (156) Amounts reclassified from accumulated other comprehensive income 10 — 10 Net current period other comprehensive (loss) income (10) (136) (146) Balance at September 30, 2023 (a) $ (2,731) $ (2,729) $ (5,460) (a) At September 30, 2024 and 2023, balances are net of deferred tax assets in pension and post-retirement plans gains (losses) of $1.5 billion and $1.3 billion, respectively. The components of other comprehensive (loss) income for the three and nine months ended September 30, 2024 and 2023 are as follows: Three Months Ended September 30, 2024 2023 (In millions) Pre-Tax Tax Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 661 $ (7) $ 668 $ (473) $ 12 $ (485) Pension/post-retirement plans: Amortization of (gains) losses included in net benefit (credit) cost: Net actuarial losses (a) 6 2 4 5 1 4 Subtotal 6 2 4 5 1 4 Foreign currency translation adjustments (180) (44) (136) 102 26 76 Effect of settlement 1 — 1 — — — Pension/post-retirement plans (losses) gains (173) (42) (131) 107 27 80 Other comprehensive income (loss) $ 488 $ (49) $ 537 $ (366) $ 39 $ (405) (a) Included in other net benefit credits in the consolidated statements of income. Income tax expense on net actuarial losses are included in income tax expense. Nine Months Ended September 30, 2024 2023 (In millions) Pre-Tax Tax Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 389 $ 4 $ 385 $ (131) $ 5 $ (136) Pension/post-retirement plans: Amortization of (gains) losses included in net benefit (credit) cost: Prior service credits (a) (1) — (1) (1) — (1) Net actuarial losses (a) 19 5 14 15 4 11 Subtotal 18 5 13 14 4 10 Foreign currency translation adjustments (124) (30) (94) (20) (5) (15) Effect of settlement 1 — 1 — — — Other adjustments — — — (7) (2) (5) Pension/post-retirement plans (losses) gains (105) (25) (80) (13) (3) (10) Other comprehensive income (loss) $ 284 $ (21) $ 305 $ (144) $ 2 $ (146) (a) Included in other net benefit credits in the consolidated statements of income. Income tax expense on net actuarial losses are included in income tax expense.

Acquisitions and Dispositions

Acquisitions and Dispositions	9 Months Ended
	Sep. 30, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions The Company’s acquisitions have been accounted for as business combinations. Net assets and results of operations are included in the Company’s consolidated financial statements commencing at the respective purchase closing dates. In connection with acquisitions, the Company records the estimated values of the net tangible assets and the identifiable intangible assets purchased, which typically consist of customer relationships, developed technology, trademarks and non-compete agreements. The valuation of purchased intangible assets involves significant estimates and assumptions. The Company estimates the fair value of purchased intangible assets, primarily using the income approach, by determining the present value of future cash flows over the remaining economic life of the respective assets. The significant estimates and assumptions used in this approach include the determination of the discount rate, economic life, future revenue growth rates, expected account attrition rates and earnings margins. Refinement and completion of final valuation of net assets acquired could affect the carrying value of tangible assets, goodwill and identifiable intangible assets. The Risk and Insurance Services segment completed 8 acquisitions for the nine months ended September 30, 2024: • January – Marsh acquired NOSCO Insurance Service Company Ltd., a Japan-based insurance broker that provides affinity type schemes, corporate and personal lines insurance. • March – Marsh & McLennan Agency ("MMA") acquired Louisiana-based insurance brokers, Querbes & Nelson ("Q&N") and Louisiana Companies. Q&N offers business insurance, employee benefits, and alternative risk financing consulting to a variety of businesses with specific expertise in energy services, commercial contractors, and transportation. Louisiana Companies provides business and personal lines insurance to businesses and individuals with specific expertise in the construction, manufacturing, distributor, healthcare, and hospitality industries. • May – MMA acquired AC Risk Management, a New York-based commercial lines insurance broker primarily offering property and casualty insurance to businesses with a focus on the construction industry; Perkins Insurance Agencies LLC, a Texas-based insurance broker providing commercial property and casualty and personal lines coverage to businesses, non-profits and families with expertise in the oil and gas, trucking, farm and ranch and restaurant industries; and Fisher Brown Bottrell Insurance, Inc. ("FBBI"), a Mississippi-based insurance broker providing commercial property and casualty insurance, surety and employee benefits services to businesses and individuals. • July – MMA acquired AmeriStar Agency Inc., a Minnesota-based insurance broker offering insurance coverage solutions to high-net-worth individuals and commercial clients; and Hudson Shore Group, a New Jersey-based public and private sector employee benefits broker, that specializes in public sector clients providing employee benefits, consulting, and administrative services with a focus on large group and alternative-funded benefits programs. • August – MMA acquired The Horton Group, Inc. ("Horton Group"), an Illinois-based insurance broker that offers property and casualty insurance, employee benefits consultation, and personal lines coverage to businesses and individuals. The Consulting segment completed 5 acquisitions for the nine months ended September 30, 2024: • February – Oliver Wyman Group acquired SeaTec Consulting Inc., a Georgia-based firm that provides consulting, engineering, and digital expertise across the aviation, aerospace and defense, and transportation industries. • March – Mercer acquired Vanguard's Institutional Advisory Services business unit ("Vanguard"), a Pennsylvania-based outsourced chief investment officer ("OCIO") business, that provides investment management services for not-for-profit organizations and other institutional investors in the U.S. Mercer also acquired The Talent Enterprise, a United Arab Emirates-based psychometric and talent assessment technology company, that provides talent assessment tools and talent capability development solutions. Oliver Wyman Group acquired Innopay NL B.V., a Netherlands-based consultancy firm that delivers strategy, scheme development, and execution in the domain of digital payments, open finance, digital identity and data sharing. • July – Oliver Wyman Group acquired Veritas Total Solutions, a Texas-based commodity trading advisory firm with expertise in risk, systems, analytics and artificial intelligence. Total purchase consideration for acquisitions made for the nine months ended September 30, 2024 was $1.3 billion, which consisted of cash paid of $1.1 billion and deferred and estimated contingent purchase consideration of $176 million. Contingent purchase consideration arrangements are generally based on earnings before interest, tax, depreciation and amortization ("EBITDA") or revenue targets over a period of 2 to 4 years. The fair value of contingent purchase consideration was based on projected revenue and earnings of the acquired entities. For the nine months ended September 30, 2024, the Company also paid $18 million of deferred purchase consideration and $163 million of contingent purchase consideration related to prior year acquisitions. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment until purchase accounting is finalized. The following table presents the preliminary allocation of purchase consideration to the assets acquired and liabilities assumed in 2024, based on the estimated fair values for the acquisitions as of their respective acquisition dates. Amounts in the table primarily reflect the impact of the Horton Group and FBBI acquisitions. Acquisitions through September 30, 2024 (In millions) Cash $ 1,078 Estimated fair value of deferred/contingent purchase consideration 176 Total consideration $ 1,254 Allocation of purchase price: Cash and cash equivalents $ 28 Cash and cash equivalents held in a fiduciary capacity 8 Net receivables 67 Other current assets 30 Goodwill 826 Other intangible assets 371 Fixed assets, net 5 Right of use assets 9 Other assets 2 Total assets acquired 1,346 Current liabilities 29 Fiduciary liabilities 8 Other liabilities 55 Total liabilities assumed 92 Net assets acquired $ 1,254 The purchase price allocation for assets acquired and liabilities assumed is based on estimates that are preliminary in nature and subject to adjustments, which could be material. Any necessary adjustments must be finalized during the measurement period, which for a particular asset, liability, or non-controlling interest ends once the acquirer determines that either (1) the necessary information has been obtained or (2) the information is not available. However, the measurement period for all items is limited to one year from the acquisition date. Items subject to change include: • amounts of intangible assets, fixed assets, capitalized software assets and right-of-use assets, subject to finalization of valuation efforts; • amounts for contingencies, pending the finalization of the Company’s assessment of the portfolio of contingencies; • amounts for deferred tax assets and liabilities, pending the finalization of valuations of the assets acquired, liabilities assumed and associated goodwill; and • amounts for income tax assets, receivables and liabilities, pending the filing of the acquired companies' pre-acquisition income tax returns and receipt of information from taxing authorities which may change certain estimates and assumptions used. The estimation of fair value requires numerous judgments, assumptions and estimates about future events and uncertainties, which could materially impact these values, and the related amortization, where applicable, in the Company’s results of operations. The following table provides information about other intangible assets acquired in 2024: Other intangible assets through September 30, 2024 (In millions) Amount Weighted Average Amortization Period Client relationships $ 349 12.3 years Other 22 2.8 years Total other intangible assets $ 371 The consolidated statements of income include the results of operations of acquired companies since their respective acquisition dates. The consolidated statements of income for the three and nine months ended September 30, 2024 include revenue of approximately $82 million and $144 million, respectively, and operating losses of $2 million and $5 million, respectively, for acquisitions made in 2024. The consolidated statements of income for both the three and nine months ended September 30, 2023, include revenue of approximately $50 million and $91 million respectively, and operating income of $5 million and $14 million for acquisitions made in 2023. The Company incurred approximately $20 million and $49 million of acquisition related expenses for the three and nine months ended September 30, 2024, respectively. For the three and nine months ended September 30, 2023, the Company incurred integration costs of $5 million and $32 million, respectively, for the acquisition of Westpac Banking Corporation's ("Westpac") financial advisory business, Advance Asset Management, and the transfer from Westpac of BT Financial Group's personal corporate pension funds to the Mercer Super Trust managed by Mercer Australia (referred to collectively, as the "Westpac Transaction"). The expenses for the Westpac Transaction related primarily to technology, consulting, legal and people related costs. Acquisition and integration costs are included in other operating expenses in the Company's consolidated statements of income. Pending Acquisition On September 30, 2024, the Company announced that it had reached an agreement to acquire McGriff Insurance Services, LLC ("McGriff"), an affiliate of TIH Insurance Holdings (the "Transaction"). McGriff is an insurance broking and risk management services provider in the U.S. Under the terms of the Transaction, the Company will acquire McGriff for an aggregate purchase price of $7.75 billion in cash consideration, funded by a combination of cash proceeds and debt financing. In conjunction with the Transaction, the Company expects to assume a deferred tax asset valued at approximately $500 million. The Transaction is targeted to close by the end of 2024, subject to regulatory clearance and other standard closing conditions. Dispositions On January 1, 2024, the Company sold its Mercer U.K. pension administration and U.S. health and benefits administration businesses for approximately $114 million and recorded a net gain of $21 million, which is included in revenue in the consolidated statements of income. As part of the disposition of the businesses, the Company incurred exit costs of $18 million in the first quarter of 2024. These costs are included in expenses in the Company's consolidated statements of income. Prior year acquisitions The Risk and Insurance Services segment completed 9 acquisitions in 2023: • May – Marsh acquired Austral Insurance Brokers Pty Ltd, an Australia-based insurance broker that provides risk advice services and business insurance solutions in the labor hire, mining services, transport, manufacturing, agribusiness, retail and professional services sectors. • June – Guy Carpenter acquired Re Solutions, an Israel-based reinsurance broker with actuarial and analytics capabilities and solutions, including an extensive facultative reinsurance offering, and MMA acquired SOLV Risk Solutions, LLC, a Texas-based risk management advisory services firm. • July – MMA acquired Integrity HR, Inc., a Kentucky-based human resources consulting firm and Trideo Systems, an Illinois-based risk management information systems provider for health care organizations, and Marsh acquired Asprose Corredora de Seguros, a Costa Rica-based insurance broker that provides insurance brokerage and risk advisory services to commercial organizations. • August – MMA acquired Graham Company, a Pennsylvania-based risk management consultancy and insurance and employee benefits broker, specializing in construction, real estate, manufacturing and distribution, health and human services and professional services. • September – MMA acquired Blue Water Insurance LLC, a Kentucky-based employee health and benefits insurance broker. • November – Marsh acquired HIG Australia Holdco Pty Ltd ("Honan Insurance Group"), an Australia-based insurance broker in the areas of corporate risk, employee benefits, and strata and real estate insurance. The Consulting segment completed 5 acquisitions in 2023: • March – Mercer acquired Leapgen LLC, a Minnesota-based human resources consulting technology advisory firm focused on digital strategy and transformation, workforce solutions, and improving employee experience. • April – Mercer acquired Westpac Banking Corporation’s ("Westpac") financial advisory business, Advance Asset Management, and completed the transfer from Westpac of BT Financial Group's personal and corporate pension funds to the Mercer Super Trust managed by Mercer Australia (referred to collectively, as the "Westpac Transaction"). Oliver Wyman Group acquired the business of Gorman Actuarial, Inc., a Massachusetts-based life and health actuarial consultant business. • July – Oliver Wyman Group acquired the actuarial consulting business of ISC Strategies Consulting, Inc., a Florida-based life insurance and actuarial consulting firm. • October – Mercer acquired BT Financial Group's Private Portfolio Management, an Australia-based wealth management business that provides investment solutions to not-for-profit organizations, high-net worth clients and their financial advisers. Total purchase consideration for acquisitions made for the nine months ended September 30, 2023 was $711 million, which consisted of cash paid of $682 million and deferred and estimated contingent purchase consideration of $29 million. Contingent purchase consideration arrangements are generally based primarily on EBITDA or revenue targets over a period of 2 to 4 years. For the first nine months of 2023, the Company also paid $52 million of deferred purchase consideration and $176 million of contingent purchase consideration related to acquisitions made in prior years. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment when purchase accounting is finalized. Prior year dispositions In January 2023, the Company entered into an agreement for the sale of an individual financial advisory business in Canada which was completed in May 2023. As a result, the Company recorded a loss of $17 million for the nine months ended September 30, 2023, primarily related to the write-down of the customer relationship intangible assets. The loss is included in revenue in the consolidated statements of income. In connection with the disposition of the Mercer U.S. affinity business in 2022, the Company transferred to the buyer an additional $20 million of cash and cash equivalents held in a fiduciary capacity in the first quarter of 2023. Deconsolidation of Russia In the third quarter of 2024, the Company obtained regulatory approval and completed its definite agreement to exit its businesses in Russia and transfer ownership to local management entered into in June 2022. Purchase of remaining non-controlling interest In the second quarter of 2023, the Company purchased the remaining interest in a subsidiary for $139 million. Pro-Forma Information The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company in 2024 and 2023. In accordance with accounting guidance related to pro-forma disclosures, the information presented for acquisitions made in 2024 is as if they occurred on January 1, 2023, and reflects acquisitions made in 2023, as if they occurred on January 1, 2022. The unaudited pro-forma information includes the effects of amortization of acquired intangibles in all years. The unaudited pro-forma financial data is presented for illustrative purposes only and is not necessarily indicative of the operating results that would have been achieved if such acquisitions had occurred on the dates indicated, nor is it necessarily indicative of future consolidated results. Three Months Ended Nine Months Ended (In millions, except per share data) 2024 2023 2024 2023 Revenue $ 5,707 $ 5,494 $ 18,535 $ 17,621 Net income attributable to the Company $ 755 $ 749 $ 3,309 $ 3,065 Basic net income per share attributable to the Company $ 1.54 $ 1.52 $ 6.73 $ 6.20 Diluted net income per share attributable to the Company $ 1.52 $ 1.50 $ 6.67 $ 6.14

Goodwill and Other Intangibles

Goodwill and Other Intangibles	9 Months Ended
	Sep. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Other Intangibles	Goodwill and Other Intangibles The Company is required to assess goodwill and any indefinite-lived intangible assets for impairment annually, or more frequently if circumstances indicate an impairment may have occurred. The Company performs the annual impairment assessment for each of its reporting units during the third quarter of each year. The reporting unit level is defined at the same level as the Company's operating segments. In accordance with applicable accounting guidance, a company can assess qualitative factors to determine whether it is necessary to perform a quantitative goodwill impairment test. Alternatively, a company may elect to proceed directly to the quantitative goodwill impairment test. In the third quarter of 2024, the Company completed a qualitative impairment assessment and concluded that goodwill was not impaired. As part of its assessment, the Company considered numerous factors, including: • that the fair value of each reporting unit exceeds its carrying value by a substantial margin based on its most recent quantitative assessment in 2023; • whether significant acquisitions or dispositions occurred which might alter the fair value of its reporting units; • macroeconomic conditions and their potential impact on reporting unit fair values; • actual performance compared with budget and prior projections used in its estimation of reporting unit fair values; • industry and market conditions; and • the year-over-year change in the Company’s share price. Other intangible assets that are not deemed to have an indefinite life are amortized over their estimated lives and assessed for impairment upon the occurrence of certain triggering events in accordance with applicable accounting literature. Based on its assessment, the Company concluded that other intangible assets were not impaired. The Company had no indefinite lived intangible assets at September 30, 2024 and December 31, 2023. Changes in the carrying amount of goodwill are as follows: (In millions) 2024 2023 Balance at January 1, $ 17,231 $ 16,251 Goodwill acquired 826 480 Other adjustments (a) 178 (76) Balance at September 30, $ 18,235 $ 16,655 (a) Primarily reflects the impact of foreign exchange. The goodwill from acquisitions in 2024 and 2023 consists largely of the synergies and economies of scale expected from combining the operations of the Company and the acquired entities and the trained and assembled workforce acquired. The goodwill acquired in 2024 included approxi mately $263 million and $88 million in t he Risk and Insurance Services and Consulting segments, respectively, which is deductible for tax purposes. Goodwill allocated to the Company’s reportable segments at September 30, 2024 is $14.0 billion for Risk and Insurance Services and $4.2 billion for Consulting. The gross cost and accumulated amortization of other identified intangible assets at September 30, 2024 and December 31, 2023 are as follows: September 30, 2024 December 31, 2023 (In millions) Gross Accumulated Net Gross Accumulated Net Client relationships $ 4,614 $ 1,937 $ 2,677 $ 4,337 $ 1,761 $ 2,576 Other (a) 386 343 43 391 337 54 Other intangible assets $ 5,000 $ 2,280 $ 2,720 $ 4,728 $ 2,098 $ 2,630 (a) Primarily reflects non-compete agreements, trade names and developed technology. Aggregate amortization expense for the three and nine months ended September 30, 2024 was $90 million and $269 million, respectively, compared to $85 million and $257 million, respectively, for the corresponding periods in the prior year. The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2024 (excludes amortization through September 30, 2024) $ 91 2025 337 2026 317 2027 308 2028 285 Subsequent years 1,382 Total future amortization $ 2,720

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements Fair Value Hierarchy The Company has categorized its assets and liabilities that are valued at fair value on a recurring basis into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets and liabilities (Level 1) and lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy, for disclosure purposes, is determined based on the lowest level input that is significant to the fair value measurement. Assets and liabilities recorded in the consolidated balance sheets at fair value are categorized based on the inputs in the valuation techniques as follows: Level 1. Assets and liabilities whose values are based on unadjusted quoted prices for identical assets or liabilities in an active market (examples include active exchange-traded equity securities and exchange-traded money market mutual funds). Assets and liabilities measured using Level 1 inputs include exchange-traded equity securities, exchange-traded mutual funds and money market funds. Level 2. Assets and liabilities whose values are based on the following: a) quoted prices for similar assets or liabilities in active markets; b) quoted prices for identical or similar assets or liabilities in non-active markets (examples include corporate and municipal bonds, which trade infrequently); c) pricing models whose inputs are observable for substantially the full term of the asset or liability (examples include most over-the-counter derivatives, including interest rate and currency swaps); and d) pricing models whose inputs are derived principally from or corroborated by observable market data through correlation or other means for substantially the full asset or liability (for example, certain mortgage loans). Level 3. Assets and liabilities whose values are based on prices, or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs reflect management’s own assumptions about the assumptions a market participant would use in pricing the asset or liability. Assets and liabilities measured using Level 3 inputs relate to assets and liabilities for contingent purchase consideration. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued at a readily determinable price. Contingent Purchase Consideration Assets and Liabilities – Level 3 Purchase consideration for some acquisitions and dispositions made by the Company include contingent consideration arrangements. Contingent consideration arrangements are based primarily on EBITDA or revenue targets over a period of 2 to 4 years. The fair value of the contingent purchase consideration asset and liability is estimated as the present value of future cash flows to be paid, based on projections of revenue and earnings and related targets of the acquired and disposed entities. The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis at September 30, 2024 and December 31, 2023: Identical Assets Observable Inputs Unobservable Inputs Total (In millions) 09/30/24 12/31/23 09/30/24 12/31/23 09/30/24 12/31/23 09/30/24 12/31/23 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 8 $ 5 $ — $ — $ — $ — $ 8 $ 5 Mutual funds (a) 189 178 — — — — 189 178 Money market funds (b) 440 606 — — — — 440 606 Contingent purchase consideration assets (c) — — — — — 1 — 1 Total assets measured at fair value $ 637 $ 789 $ — $ — $ — $ 1 $ 637 $ 790 Fiduciary Assets: Money market funds $ 66 $ 180 $ — $ — $ — $ — $ 66 $ 180 Total fiduciary assets measured $ 66 $ 180 $ — $ — $ — $ — $ 66 $ 180 Liabilities: Contingent purchase consideration liabilities (d) $ — $ — $ — $ — $ 168 $ 252 $ 168 $ 252 Total liabilities measured at fair value $ — $ — $ — $ — $ 168 $ 252 $ 168 $ 252 (a) Included in other assets in the consolidated balance sheets. (b) Included in cash and cash equivalents in the consolidated balance sheets. (c) Included in other receivables in the consolidated balance sheets. (d) Included in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets. The Level 3 assets in the table reflect contingent purchase consideration from the sale of businesses. During the nine months ended September 30, 2024 and 2023, there were no assets or liabilities that were transferred between levels. The change in the contingent purchase consideration assets from December 31, 2023 is driven primarily by cash receipts of approximately $1 million. The following table sets forth a summary of the changes in fair value of the Company’s Level 3 liabilities for the three and nine months ended September 30, 2024 and 2023: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Balance at beginning of period $ 121 $ 223 $ 252 $ 377 Net additions 43 5 60 9 Payments (2) (1) (163) (176) Revaluation impact 6 4 21 21 Other — — (2) — Balance at end of period $ 168 $ 231 $ 168 $ 231 Long-Term Investments The Company has investments in public and private companies as well as certain private equity investments that are accounted for using the equity method of accounting. The carrying value of these investments was $275 million and $266 million at September 30, 2024 and December 31, 2023, respectively. Investments in Public and Private Companies The Company has investments in private insurance and consulting companies with a carrying value of $74 million and $63 million at September 30, 2024 and December 31, 2023, respectively. These investments are accounted for using the equity method of accounting, the results of which are included in revenue in the consolidated statements of income and the carrying value of which is included in other assets in the consolidated balance sheets. The Company records its share of income or loss on its equity method investments, some of which are on a one quarter lag basis. Private Equity Investments The Company's investments in private equity funds were $201 million and $203 million at September 30, 2024 and December 31, 2023, respectively. The carrying values of these private equity investments approximate fair value. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. The Company records in earnings its proportionate share of the change in fair value of the funds on the investment income line in the consolidated statements of income. These investments are included in other assets in the consolidated balance sheets. At September 30, 2024, the Company has commitments of potential future investments of approximately $120 million in private equity funds that invest primarily in financial services companies. Other Investments The Company held equity investments with readily determinable market values at September 30, 2024 and December 31, 2023, of $19 million and $16 million, respectively.

Derivatives

Derivatives	9 Months Ended
	Sep. 30, 2024
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives Net Investment Hedge The Company has investments in various subsidiaries with Euro functional currencies. As a result, the Company is exposed to the risk of fluctuations between the Euro and U.S. dollar exchange rates. The Company designated its €1.1 billion senior note debt instruments ("Euro notes") as a net investment hedge (the "hedge") of its Euro denominated subsidiaries. The hedge effectiveness is re-assessed each quarter to confirm that the designated equity balance at the beginning of each period continues to equal or exceed 80% of the outstanding balance of the Euro debt instrument and that all the critical terms of the hedging instrument and the hedged net investment continue to match. If the hedge is highly effective, the change in the debt balance related to foreign exchange fluctuations is recorded in accumulated other comprehensive loss in the consolidated balance sheets.

Leases

Leases	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Leases	Leases The Company leases office facilities under non-cancelable operating leases with terms generally ranging between 10 and 25 years. The Company utilizes these leased office facilities for use by its employees in countries in which the Company conducts its business. The Company’s leases have no restrictions on the payment of dividends, the acquisition of debt or additional lease obligations, or entering into additional lease obligations. The leases also do not contain significant purchase options. Operating leases are recognized on the consolidated balance sheets as ROU assets and operating lease liabilities based on the present value of the remaining future minimum payments over the lease term at commencement date of the lease. For the three and nine months ended September 30, 2024 and 2023, the Company determined that $7 million and $9 million, respectively, and $6 million and $19 million, respectively, of the ROU assets were impaired and recorded a charge to the consolidated statements of income with an offsetting reduction to ROU assets. The following table provides additional information about the Company’s property leases: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Lease Cost: Operating lease cost (a) $ 84 $ 82 $ 247 $ 243 Short-term lease cost 1 1 4 4 Variable lease cost 31 31 85 94 Sublease income (2) (2) (10) (8) Net lease cost $ 114 $ 112 $ 326 $ 333 Other information: Operating cash outflows from operating leases $ 278 $ 284 Right of use assets obtained in exchange for new operating lease liabilities $ 135 $ 177 Weighted average remaining lease term – real estate 7.8 years 8.1 years Weighted average discount rate – real estate leases 3.64 % 3.28 % (a) Excludes ROU asset impairment charges. Future minimum lease payments for the Company’s operating leases at September 30, 2024 are as follows: (In millions) Real Estate Leases 2024 (excludes payments through September 30, 2024) $ 95 2025 371 2026 343 2027 305 2028 229 2029 183 Subsequent years 678 Total future lease payments 2,204 Less: Imputed interest (273) Total $ 1,931 Current lease liabilities $ 313 Long-term lease liabilities 1,618 Total lease liabilities $ 1,931 Note: The above table excludes obligations for leases with original terms of 12 months or less which have not been recognized as a ROU asset or liability in the consolidated balance sheets.

Retirement Benefits

Retirement Benefits	9 Months Ended
	Sep. 30, 2024
Retirement Benefits [Abstract]
Retirement Benefits	Retirement Benefits The Company maintains qualified and non-qualified defined benefit pension plans for its U.S. and non-U.S. eligible employees. The Company’s policy for funding its tax-qualified defined benefit retirement plans is to contribute amounts at least sufficient to meet the funding requirements set forth by U.S. law and the laws of the non-U.S. jurisdictions in which the Company offers defined benefit plans. The weighted average actuarial assumptions utilized to calculate the net periodic benefit costs for the U.S. and significant non-U.S. defined benefit plans are as follows: Combined U.S. and significant non-U.S. Plans Pension Benefits September 30, 2024 2023 Weighted average assumptions: Expected return on plan assets 5.44 % 5.31 % Discount rate 4.95 % 5.16 % Rate of compensation increase * 3.16 % 3.16 % (*) There are no rate of compensation increase assumptions for the U.S. defined benefit plans since future benefit accruals were discontinued for those plans after December 31, 2016 and earned benefits are not subject to final salary level adjustments. The target asset allocation for the U.S. plans is 50% equities and equity alternatives, and 50% fixed income. At September 30, 2024, the actual allocation for the U.S. plans was 50% equities and equity alternatives, and 50% fixed income. The target allocation for the U.K. plans at September 30, 2024 is 13% equities and equity alternatives, and 87% fixed income. At September 30, 2024, the actual allocation for the U.K. plans was 14% equities and equity alternatives and 86% fixed income. The Company's U.K. plans comprised approximately 79% of non-U.S. plan assets at December 31, 2023. The assets of the Company's defined benefit plans are diversified and are managed in accordance with applicable laws and with the goal of maximizing the plans' real return within acceptable risk parameters. The Company uses threshold-based portfolio re-balancing to ensure the actual portfolio remains consistent with target asset allocation ranges. The net benefit cost or credit of the Company's defined benefit plans is measured on an actuarial basis using various methods and assumptions. The components of the net benefit credit for defined benefit plans are as follows: Combined U.S. and significant non-U.S. Plans For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 5 $ 7 Interest cost 146 151 Expected return on plan assets (222) (218) Recognized actuarial loss 8 5 Net periodic benefit credit $ (63) $ (55) Settlement loss 1 — Net benefit credit $ (62) $ (55) Combined U.S. and significant non-U.S. Plans For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 17 $ 18 Interest cost 434 449 Expected return on plan assets (657) (645) Amortization of prior service cost 1 — Recognized actuarial loss 23 16 Net periodic benefit credit $ (182) $ (162) Settlement loss 1 — Net benefit credit $ (181) $ (162) The following tables provide the amounts reported in the consolidated statements of income: Combined U.S. and significant non-U.S. Plans For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Compensation and benefits expense $ 5 $ 7 Other net benefit credits (67) (62) Net benefit credit $ (62) $ (55) Combined U.S. and significant non-U.S. Plans For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Compensation and benefits expense $ 17 $ 18 Other net benefit credits (198) (180) Net benefit credit $ (181) $ (162) The components of the net benefit credit for the U.S. defined benefit plans are as follows: U.S. Plans only For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Interest cost $ 62 $ 65 Expected return on plan assets (76) (78) Recognized actuarial loss 5 5 Net benefit credit $ (9) $ (8) U.S. Plans only For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Interest cost $ 187 $ 195 Expected return on plan assets (227) (233) Recognized actuarial loss 15 14 Net benefit credit $ (25) $ (24) The components of the net benefit credit for the non-U.S. defined benefit plans are as follows: Significant non-U.S. Plans only For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 5 $ 7 Interest cost 84 86 Expected return on plan assets (146) (140) Recognized actuarial loss 3 — Net periodic benefit credit $ (54) $ (47) Settlement loss 1 — Net benefit credit $ (53) $ (47) Significant non-U.S. Plans only For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 17 $ 18 Interest cost 247 254 Expected return on plan assets (430) (412) Amortization of prior service cost 1 — Recognized actuarial loss 8 2 Net periodic benefit credit $ (157) $ (138) Settlement loss 1 — Net benefit credit $ (156) $ (138) The Company made contributions to its U.S. and non-U.S. defined benefit pension plans for the three and nine months ended September 30, 2024 of approximately $16 million and $67 million, respectively, compared to contributions of $26 million and $73 million, respectively, for the corresponding periods in the prior year. The Company expects to contribute approximately $25 million to its U.S. and non-U.S. defined benefit pension plans during the remainder of 2024. Defined Contribution Plans The Company maintains defined contribution plans ("DC Plans") for its employees, the most significant being in the U.S. and the U.K. The cost of the U.S. DC Plans for the three and nine months ended September 30, 2024 was $45 million and $142 million, respectively, and $45 million and $133 million, respectively, for the corresponding periods in the prior year. The cost of the U.K. DC Plans for the three and nine months ended September 30, 2024 was $39 million and $130 million, respectively, and $39 million and $120 million, respectively, for the corresponding periods in the prior year.

Debt

Debt	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Debt	Debt The Company’s outstanding debt is as follows: (In millions) September 30, December 31, 2023 Short-term: Current portion of long-term debt $ 518 $ 1,619 $ 518 $ 1,619 Long-term: Senior notes – 3.50% due 2024 $ — $ 600 Senior notes – 3.875% due 2024 — 1,000 Senior notes – 3.50% due 2025 500 499 Senior notes – 1.349% due 2026 623 617 Senior notes – 3.75% due 2026 599 599 Senior notes – 4.375% due 2029 1,499 1,499 Senior notes – 1.979% due 2030 603 601 Senior notes – 2.25% due 2030 742 741 Senior notes – 2.375% due 2031 397 397 Senior notes – 5.750% due 2032 493 493 Senior notes – 5.875% due 2033 298 298 Senior notes – 5.400% due 2033 593 592 Senior notes – 5.150% due 2034 495 — Senior notes – 4.75% due 2039 496 496 Senior notes – 4.35% due 2047 494 494 Senior notes – 4.20% due 2048 593 593 Senior notes – 4.90% due 2049 1,239 1,239 Senior notes – 2.90% due 2051 346 346 Senior notes – 6.25% due 2052 491 491 Senior notes – 5.450% due 2053 591 591 Senior notes – 5.700% due 2053 988 988 Senior notes – 5.450% due 2054 493 — Mortgage – 5.70% due 2035 271 284 Other 4 5 12,848 13,463 Less: current portion 518 1,619 $ 12,330 $ 11,844 The senior notes in the table above are registered by the Company with the Securities and Exchange Commission and are not guaranteed. In November 2023, the Company increased its short-term commercial paper financing program (the "Program") to $3.5 billion from $2.8 billion. The Company did not have any commercial paper outstanding at September 30, 2024 and December 31, 2023. Credit Facilities In October 2023, the Company increased its multi-currency unsecured five-year credit facility (the "Credit Facility") capacity to $3.5 billion from $2.8 billion and extended the expiration to October 2028. The interest rate on the Credit Facility was initially based on LIBOR plus a fixed margin which varied with the Company's credit rating. In the second quarter of 2023, the Credit Facility was amended so that borrowings under the Credit Facility bear interest at a rate per annum, equal, at the Company's option, either at (a) SOFR benchmark rate for U.S. dollar borrowings, or (b) a currency specific benchmark rate, plus an applicable margin which varies with the Company's credit ratings. The Company is required to maintain certain coverage and leverage ratios for the Credit Facility, which are evaluated quarterly. The Credit Facility includes provisions for determining a benchmark replacement rate in the event existing benchmark rates are no longer available, or in certain other circumstances, in which an alternative rate may be required. At September 30, 2024 and December 31, 2023, the Company had no borrowings under this facility. In October 2023, the Company terminated its one-year uncommitted revolving credit facility ("Uncommitted Credit Facility"). In the third quarter of 2023, the Company repaid $200 million of borrowings outstanding under this facility with a weighted average interest rate of 5.50%. There were no borrowings outstanding under the Uncommited Credit Facility at September 30, 2023. The Company also maintains other credit and overdraft facilities with various financial institutions aggregating $124 million and $113 million, at September 30, 2024 and December 31, 2023, respectively. There were no outstanding borrowings under these facilities at September 30, 2024 and December 31, 2023. The Company also has outstanding guarantees and letters of credit with various banks aggregating $153 million and $139 million, at September 30, 2024 and December 31, 2023, respectively. Senior Notes In June 2024, the Company repaid $600 million of 3.50% senior notes at maturity. In March 2024, the Company repaid $1 billion of 3.875% senior notes at maturity. In February 2024, the Company issued $500 million of 5.150% senior notes due 2034 and $500 million of 5.450% senior notes due 2054. The Company used the net proceeds from these issuances for general corporate purposes. In October 2023, the Company repaid $250 million of 4.05% senior notes at maturity. In September 2023, the Company issued $600 million of 5.400% senior notes due 2033 and $1 billion of 5.700% senior notes due 2053. In March 2023, the Company issued $600 million of 5.450% senior notes due 2053. The Company used the net proceeds from this issuance for general corporate purposes. Pending Acquisition In connection with the pending McGriff Transaction, on September 29, 2024, the Company entered into a Bridge Loan Commitment Letter (the “Commitment Letter”) to provide the Company with 100% of the loans under a 364-day unsecured bridge term loan facility in an amount not to exceed $7.75 billion (the “Bridge Loan Facility”). The Company paid approximately $23 million for customary upfront fees related to the Commitment Letter, which will be amortized as interest expense based on the period of time the Bridge Loan Facility is expected to be in effect. Any borrowing under the Bridge Loan Facility will mature 364 days from the funding date, and the Company will be required to comply with certain covenants including maintaining an interest coverage ratio and leverage ratio within specified levels. The loans will bear interest at a rate per annum, equal to, at the Company’s election, either (a) SOFR-based rate, or (b) an alternative base rate, in each case, plus an applicable margin which varies with the Company's credit ratings. At September 30, 2024, there has not been any funding of bridge loans under the Commitment Letter. The commitments under the Bridge Loan Facility are expected to be reduced, or any loans borrowed repaid, with long-term financing, equity issuances, or disposition of assets. Fair Value of Short-term and Long-term Debt The estimated fair value of the Company's short-term and long-term debt is provided below. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts shown in the following table are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or need to dispose of the financial instrument. September 30, 2024 December 31, 2023 (In millions) Carrying Fair Carrying Fair Short-term debt $ 518 $ 515 $ 1,619 $ 1,610 Long-term debt $ 12,330 $ 12,279 $ 11,844 $ 11,723 The fair value of the Company's short-term debt consists primarily of commercial and term debt maturing within the next year and its fair value approximates its carrying value. The estimated fair value of a primary portion of the Company's long-term debt is based on discounted future cash flows using current interest rates available for debt with similar terms and remaining maturities. Short-term and long-term debt would be classified as Level 2 in the fair value hierarchy.

Restructuring Costs

Restructuring Costs	9 Months Ended
	Sep. 30, 2024
Restructuring and Related Activities [Abstract]
Restructuring Costs	Restructuring Costs In the fourth quarter of 2022, the Company initiated activities focused on workforce actions, rationalization of technology and functional services, and reductions in real estate. In the third quarter of 2024, the Company finalized its detailed plans and anticipates total charges related to these activities to be approximately $650 million. The Company has incurred approximately $540 million of these restructuring costs through September 30, 2024, primarily severance and lease exit charges, of which $36 million and $96 million were incurred for the three and nine months ended September 30, 2024, respectively. The Company is expected to complete these activities by the end of 2024. The Company incurred a total of $54 million and $140 million for restructuring activities for the three and nine months ended September 30, 2024, respectively, compared to $52 million and $170 million, for the corresponding periods in the prior year. The Company incurred costs related to these initiatives as follows: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Risk and Insurance Services $ 22 $ 26 $ 73 $ 89 Consulting 14 17 30 33 Corporate 18 9 37 48 Total $ 54 $ 52 $ 140 $ 170 Details of the restructuring activity from January 1, 2023 through September 30, 2024, are as follows: (In millions) Severance Real Estate Related Costs (a) Information Technology Consulting and Other Outside Services Total Liability at January 1, 2023 $ 88 $ 56 $ — $ 2 $ 146 2023 charges 148 96 15 42 301 Cash payments (147) (69) (13) (42) (271) Non-cash charges — (44) (2) — (46) Liability at December 31, 2023 $ 89 $ 39 $ — $ 2 $ 130 2024 charges 63 41 19 17 140 Cash payments (123) (34) (19) (19) (195) Non-cash charges — (9) — — (9) Liability at September 30, 2024 $ 29 $ 37 $ — $ — $ 66 (a) Includes ROU and fixed asset impairments and other real estate related costs.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Common Stock	Common Stock The Company has a share repurchases program authorized by the Board of Directors. For the first nine months of 2024, the Company repurchased 4.3 million shares of its common stock for $900 million. At September 30, 2024, the Company remained authorized to repurchase up to approximately $2.3 billion in shares of its common stock. There is no time limit on the authorization. For the first nine months of 2023, the Company repurchased 5.1 million shares of its common stock for $900 million. The Company issued approximately 3.3 million shares related to stock compensation and employee stock purchase plans for the first nine months of both 2024 and 2023. In January and March of 2024, the Board of Directors of the Company declared quarterly dividends of $0.710 per share on outstanding common stock, which were paid in February and May 2024, respectively. In July 2024, the Board of Directors of the Company declared a quarterly dividend of $0.815 per share on outstanding common stock, paid in August 2024. In September 2024, the Board of Directors of the Company declared a quarterly dividend of $0.815 per share on outstanding common stock, payable in November 2024.

Claims, Lawsuits and Other Cont

Claims, Lawsuits and Other Contingencies	9 Months Ended
	Sep. 30, 2024
Commitments and Contingencies Disclosure [Abstract]
Claims, Lawsuits and Other Contingencies	Claims, Lawsuits and Other Contingencies Nature of Contingencies The Company and its subsidiaries are subject to a significant number of claims, lawsuits and proceedings in the course of our business. Such claims and lawsuits consist principally of alleged errors and omissions in connection with the performance of professional services, including the placement of insurance, the provision of actuarial services for corporate and public sector clients, the provision of investment advice and investment management services to pension plans, the provision of advice relating to pension buy-out transactions and the provision of consulting services relating to the drafting and interpretation of trust deeds and other documentation governing pension plans. These claims often seek damages, including punitive and treble damages, in amounts that could be significant. In establishing liabilities for errors and omissions claims, the Company utilizes case level reviews by inside and outside counsel, and internal actuarial analysis by Oliver Wyman Group, a subsidiary of the Company, and other methods to estimate potential losses. A liability is established when a loss is both probable and reasonably estimable. The liability is reviewed quarterly and adjusted as developments warrant. In many cases, the Company has not recorded a liability, other than for legal fees to defend the claim, because we are unable, at the present time, to make a determination that a loss is both probable and reasonably estimable. To the extent that expected losses exceed our deductible in any policy year, the Company also records an asset for the amount that we expect to recover under any available third-party insurance programs. The Company has varying levels of third-party insurance coverage, with policy limits and coverage terms varying significantly by policy year. Our activities are regulated under the laws of the U.S. and its various states, the U.K., the European Union (E.U.) and its member states, and the many other jurisdictions in which the Company operates. The Company also receives subpoenas in the ordinary course of business, and from time to time requests for information in connection with government investigations. Current Matters Risk and Insurance Services Segment • In January 2019, the Company received a notice that the Administrative Council for Economic Defense anti-trust agency in Brazil had commenced an administrative proceeding against a number of insurance brokers, including both Marsh and JLT, and insurers "to investigate an alleged sharing of sensitive commercial and competitive confidential information" in the aviation insurance and reinsurance sector. • From 2014, Marsh Ltd. was engaged by Greensill Capital (UK) Limited and its affiliates as its insurance broker. Marsh Ltd. placed a number of trade credit insurance policies for Greensill. On March 1, 2021, Greensill filed an action against certain of its trade credit insurers in Australia seeking a mandatory injunction compelling these insurers to renew coverage under expiring policies. Later that day, the Australian court denied Greensill’s application. Since then, a number of Greensill entities have filed for, or been subject to, insolvency proceedings, and several litigations and investigations have been commenced in the U.K., Australia, Germany, Switzerland and the U.S., including claims brought by Greensill's administrators and loss payees under Greensill's trade credit insurance policies. In June 2023, White Oak, one such loss payee, filed a claim in the High Court of Justice in London against Marsh Ltd., related to White Oak’s purchase of accounts receivable from Greensill. In November 2023, Credit Suisse, another loss payee, added Marsh Ltd. as a party to the omnibus trade credit insurance policy litigation among Greensill and its insurers and loss payees in Australia. The claims by both loss payees allege that Marsh Ltd., which was not the insurance broker for either White Oak or Credit Suisse, failed to take required steps to make complete and accurate representations to them in their respective capacities as loss payees. Other Contingencies-Guarantees In connection with its acquisition of U.K.-based Sedgwick Group in 1998, the Company acquired several insurance underwriting businesses that were already in run-off, including River Thames Insurance Company Limited ("River Thames"), which the Company sold in 2001. Sedgwick guaranteed payment of claims on certain policies underwritten through the Institute of London Underwriters (the "ILU") by River Thames. The policies covered by this guarantee are partly reinsured by a related party of River Thames. Payment of claims under the reinsurance agreement is collateralized by funds withheld by River Thames from the reinsurer. To the extent River Thames or the reinsurer is unable to meet its obligations under those policies, a claimant may seek to recover from the Company under the guarantee. From 1980 to 1983, the Company owned indirectly the English & American Insurance Company ("E&A"), which was a member of the ILU. The ILU required the Company to guarantee a portion of E&A's obligations. After E&A became insolvent in 1993, the ILU agreed to discharge the guarantee in exchange for the Company's agreement to post an evergreen letter of credit that is available to pay claims by policyholders on certain E&A policies issued through the ILU and incepting between July 3, 1980 and October 6, 1983. Certain claims have been paid under the letter of credit and the Company anticipates that additional claimants may seek to recover against the letter of credit. * * * * * The pending proceedings described above and other matters not explicitly described in this Note 17 on Claims, Lawsuits and Other Contingencies may expose the Company or its subsidiaries to liability for significant monetary damages, fines, penalties or other forms of relief. Where a loss is both probable and reasonably estimable, the Company establishes liabilities in accordance with the Financial Accounting Standards Board ("FASB") guidance on Contingencies - Loss Contingencies. The Company is not able at this time to provide a reasonable estimate of the range of possible loss attributable to these matters or the impact they may have on the Company's consolidated results of operations, financial position or cash flows. This is primarily because these matters are still developing and involve complex issues subject to inherent uncertainty. Adverse determinations in one or more of these matters could have a material impact on the Company's consolidated results of operations, financial condition or cash flows in a future period.

Segment Information

Segment Information	9 Months Ended
	Sep. 30, 2024
Segment Reporting [Abstract]
Segment Information	Segment Information The Company is organized based on the types of services provided. Under this structure, the Company’s segments are: • Risk and Insurance Services , comprising insurance services (Marsh) and reinsurance services (Guy Carpenter); and • Consulting , comprising Mercer and Oliver Wyman Group. The accounting policies of the segments are the same as those used for the consolidated financial statements described in Note 1, Summary of Significant Accounting Policies, in the Company’s 2023 Form 10-K. Segment performance is evaluated based on segment operating income, which includes directly related expenses, and charges or credits related to restructuring but not the Company’s corporate-level expenses. Revenues are attributed to geographic areas on the basis of where the services are performed. Selected information about the Company’s segments for the three and nine months ended September 30, 2024 and 2023 is as follows: Three Months Ended Nine Months Ended (In millions) Revenue Operating Income/(Loss) Revenue Operating Income/(Loss) 2024 – Risk and Insurance Services $ 3,453 (a) $ 733 $ 11,748 (c) $ 3,595 Consulting 2,262 (b) 462 6,692 (d) 1,304 Total Segments 5,715 1,195 18,440 4,899 Corporate/Eliminations (18) (87) (49) (224) Total Consolidated $ 5,697 $ 1,108 $ 18,391 $ 4,675 2023 – Risk and Insurance Services $ 3,190 (a) $ 640 $ 10,818 (c) $ 3,192 Consulting 2,206 (b) 424 6,409 (d) 1,223 Total Segments 5,396 1,064 17,227 4,415 Corporate/Eliminations (14) (68) (45) (236) Total Consolidated $ 5,382 $ 996 $ 17,182 $ 4,179 (a) Includes interest income on fiduciary funds of $138 million and $131 million in 2024 and 2023, respectively, and equity method income of $7 million and $3 million in 2024 and 2023, respectively. (b) Includes inter-segment revenue of $18 million and $14 million in 2024 and 2023, respectively. (c) Includes inter-segment revenue of $5 million in both 2024 and 2023, interest income on fiduciary funds of $385 million and $330 million in 2024 and 2023, respectively, and equity method income of $17 million and $14 million in 2024 and 2023, respectively. (d) Includes inter-segment revenue of $44 million and $40 million in 2024 and 2023, respectively. Revenue in 2024 also includes a net gain of $21 million from the sale of Mercer's U.K. pension administration and U.S. health and benefits administration businesses. Details of operating segment revenue for the three and nine months ended September 30, 2024 and 2023 are as follows: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Risk and Insurance Services Marsh $ 3,023 $ 2,782 $ 9,446 $ 8,685 Guy Carpenter 430 408 2,302 2,133 Total Risk and Insurance Services 3,453 3,190 11,748 10,818 Consulting Mercer 1,452 1,425 4,256 4,143 Oliver Wyman Group 810 781 2,436 2,266 Total Consulting 2,262 2,206 6,692 6,409 Total Segments 5,715 5,396 18,440 17,227 Corporate Eliminations (18) (14) (49) (45) Total $ 5,697 $ 5,382 $ 18,391 $ 17,182

New Accounting Pronouncements

New Accounting Pronouncements	9 Months Ended
	Sep. 30, 2024
Accounting Standards Update and Change in Accounting Principle [Abstract]
New Accounting Pronouncements	New Accounting Pronouncements Recently Issued Accounting Pronouncements Not Yet Adopted In December 2023, the FASB issued an accounting standard update on income tax disclosures, primarily related to the rate reconciliation and income taxes paid information. The new guidance requires that public business entities, on an annual basis, disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. In addition, all entities are required to disclose on an annual basis the amount of income taxes paid, net of refunds received, disaggregated by federal, state and foreign taxes, and by individual jurisdictions if the amount is equal to or greater than 5% of total income taxes paid, net of refunds received. The guidance is effective for annual periods beginning after December 15, 2024. Early adoption is permitted. An entity should apply the amendments in the standard prospectively, even though retrospective application is permitted. The Company is currently evaluating the guidance and expects it to only impact disclosures with no impact to results of operations, cash flows, or financial condition.

Principles of Consolidation a_2

Principles of Consolidation and Other Matters (Policies)	9 Months Ended
	Sep. 30, 2024
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and Cash Equivalents	Cash and Cash Equivalents
Allowance for Credit Losses on Accounts Receivable	Allowance for Credit Losses on Accounts Receivable
Investments	Investments The caption "Investment income" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds.
Income Taxes	Income Taxes The Company's effective tax rate for the three months ended September 30, 2024 was 27.3%, compared with 20.6% for the corresponding quarter of 2023. The effective tax rates for the nine months ended September 30, 2024 and 2023 were 25.8% and 23.7%, respectively. The tax rate in each period reflects the impact of discrete tax items such as excess tax benefits related to share-based compensation, enacted tax legislation, changes in uncertain tax positions, deferred tax adjustments, non-taxable adjustments related to contingent consideration for acquisitions, and valuation allowances for certain tax credits and attributes. The rate for the three and nine months ended September 30, 2024 reflects the previously enacted change in the United Kingdom (U.K.) corporate income tax rate from 19% to 25%, which was effective April 1, 2023. The blended U.K. statutory tax rate for 2023 was 23.5%. The excess tax benefit related to share-based payments is the most significant discrete item for the nine months ended September 30, 2024 and 2023, reducing the effective tax rate by 1.3% and 1.2%, respectively. The reduction to the effective tax rate for the three months ended September 30, 2024 and 2023 is 0.3% and 1.0%, respectively. During the third quarter of 2023, the Company released a valuation allowance related to the realizability of deferred tax assets for its non-U.S. operations of $48 million as a discrete tax benefit, primarily due to the sustained profitability of its operations. This was the most significant discrete item for the three months ended September 30, 2023, reducing the effective tax rate by 4.8%. For the nine months ended September 30, 2023, the reduction to the effective tax rate was 1.1%. The Company's tax rate reflects its income, statutory tax rates, and tax planning in the various jurisdictions in which it operates. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions. Losses in one jurisdiction, generally, cannot offset earnings in another, and within certain jurisdictions profits and losses may not offset between entities. Consequently, losses in certain jurisdictions may require valuation allowances affecting the effective tax rate, depending on estimates of the realizability of associated deferred tax assets. The tax rate is also sensitive to changes in unrecognized tax benefits, including the impact of settled tax audits and expired statutes of limitations. The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in tax returns. The Company's gross unrecognized tax benefits were $122 million at September 30, 2024, and $124 million at December 31, 2023. It is reasonably possible that the total amount of unrecognized tax benefits could decrease up to approximately $66 million within the next twelve months due to settlement of audits and expirations of statutes of limitations. In the third quarter of 2024, the Company received closure notices and assessments from the U.K. tax authority in relation to its 2016-2020 examinations which disallowed certain interest expense deductions. The Company has appealed the assessments and resolving this matter through litigation or alternative dispute resolution may take several years. The Company believes the resolution of tax matters will not have a material effect on the consolidated financial position of the Company. However, an adverse resolution of tax matters could have a material impact on the Company's net income or cash flows and on its effective tax rate in a particular future period.
Restructuring Costs	Restructuring Costs Charges associated with restructuring activities are recognized in accordance with applicable accounting guidance which includes accounting for disposal or exit activities, guidance related to impairment of right-of-use ("ROU") assets related to real estate leases, as well as other costs resulting from accelerated depreciation or amortization of leasehold improvements and other property and equipment. Severance and related costs are recognized based on amounts due under established severance plans or estimates of one-time benefits that will be provided. Typically, severance benefits are recognized when the impacted colleagues are notified of their expected termination and such termination is expected to occur within the legally required notification period. These costs are included in compensation and benefits in the consolidated statements of income. Costs for real estate consolidation are recognized based on the type of cost, and the expected future use of the facility. For locations where the Company does not expect to sub-lease the property, the amortization of any ROU asset is accelerated from the decision date to the cease use date. For locations where the Company expects to sub-lease the properties subsequent to its vacating the property, the ROU asset is reviewed for potential impairment at the earlier of the cease use date or the date a sub-lease is signed. To determine the amount of impairment, the fair value of the ROU asset is determined based on the present value of the estimated net cash flows related to the property. Contractual costs outside of the ROU asset are recognized based on the net present value of expected future cash outflows for which the Company will not receive any benefit. Such amounts are reliant on estimates of future sub-lease income to be received and future contractual costs to be incurred. These costs are included in other operating expenses in the consolidated statements of income. Other costs related to restructuring, such as moving, legal or consulting costs are recognized as incurred. These costs are included in other operating expenses in the consolidated statements of income.
Foreign Currency	Foreign Currency
Revenue	Revenue The core principle of the revenue recognition guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this principle, the entity applies the following steps: identify the contract(s) with the customer, identify the performance obligations in the contract(s), determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. In accordance with the accounting guidance, a performance obligation is satisfied either at a "point in time" or "over time", depending on the nature of the product or service provided, and the specific terms of the contract with customers.
Fair Value Measurements	Fair Value Measurements Fair Value Hierarchy The Company has categorized its assets and liabilities that are valued at fair value on a recurring basis into a three-level fair value hierarchy. The fair value hierarchy gives the highest priority to quoted prices in active markets for identical assets and liabilities (Level 1) and lowest priority to unobservable inputs (Level 3). In some cases, the inputs used to measure fair value might fall into different levels of the fair value hierarchy. In such cases, the level in the fair value hierarchy, for disclosure purposes, is determined based on the lowest level input that is significant to the fair value measurement. Assets and liabilities recorded in the consolidated balance sheets at fair value are categorized based on the inputs in the valuation techniques as follows: Level 1. Assets and liabilities whose values are based on unadjusted quoted prices for identical assets or liabilities in an active market (examples include active exchange-traded equity securities and exchange-traded money market mutual funds). Assets and liabilities measured using Level 1 inputs include exchange-traded equity securities, exchange-traded mutual funds and money market funds. Level 2. Assets and liabilities whose values are based on the following: a) quoted prices for similar assets or liabilities in active markets; b) quoted prices for identical or similar assets or liabilities in non-active markets (examples include corporate and municipal bonds, which trade infrequently); c) pricing models whose inputs are observable for substantially the full term of the asset or liability (examples include most over-the-counter derivatives, including interest rate and currency swaps); and d) pricing models whose inputs are derived principally from or corroborated by observable market data through correlation or other means for substantially the full asset or liability (for example, certain mortgage loans). Level 3. Assets and liabilities whose values are based on prices, or valuation techniques that require inputs that are both unobservable and significant to the overall fair value measurement. These inputs reflect management’s own assumptions about the assumptions a market participant would use in pricing the asset or liability. Assets and liabilities measured using Level 3 inputs relate to assets and liabilities for contingent purchase consideration. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued at a readily determinable price. Contingent Purchase Consideration Assets and Liabilities – Level 3 Purchase consideration for some acquisitions and dispositions made by the Company include contingent consideration arrangements. Contingent consideration arrangements are based primarily on EBITDA or revenue targets over a period of 2 to 4 years. The fair value of the contingent purchase consideration asset and liability is estimated as the present value of future cash flows to be paid, based on projections of revenue and earnings and related targets of the acquired and disposed entities.
Recently Issued Accounting Pronouncements Not Yet Adopted	Recently Issued Accounting Pronouncements Not Yet Adopted In December 2023, the FASB issued an accounting standard update on income tax disclosures, primarily related to the rate reconciliation and income taxes paid information. The new guidance requires that public business entities, on an annual basis, disclose specific categories in the rate reconciliation and provide additional information for reconciling items that meet a quantitative threshold. In addition, all entities are required to disclose on an annual basis the amount of income taxes paid, net of refunds received, disaggregated by federal, state and foreign taxes, and by individual jurisdictions if the amount is equal to or greater than 5% of total income taxes paid, net of refunds received. The guidance is effective for annual periods beginning after December 15, 2024. Early adoption is permitted. An entity should apply the amendments in the standard prospectively, even though retrospective application is permitted. The Company is currently evaluating the guidance and expects it to only impact disclosures with no impact to results of operations, cash flows, or financial condition.

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2024
Revenue from Contract with Customer [Abstract]
Schedule of Disaggregation of Revenue	The following table disaggregates various components of the Company's revenue: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Marsh: EMEA $ 747 $ 692 $ 2,684 $ 2,482 Asia Pacific 342 311 1,069 980 Latin America 134 134 396 386 Total International 1,223 1,137 4,149 3,848 U.S./Canada 1,711 1,563 5,053 4,634 Total Marsh 2,934 2,700 9,202 8,482 Guy Carpenter 381 359 2,161 2,006 Subtotal 3,315 3,059 11,363 10,488 Fiduciary interest income 138 131 385 330 Total Risk and Insurance Services $ 3,453 $ 3,190 $ 11,748 $ 10,818 Mercer: Wealth $ 625 $ 635 $ 1,909 $ 1,853 Health 520 496 1,605 1,559 Career 307 294 742 731 Total Mercer 1,452 1,425 4,256 4,143 Oliver Wyman Group 810 781 2,436 2,266 Total Consulting $ 2,262 $ 2,206 $ 6,692 $ 6,409
Schedule of Contract Assets and Liabilities	The following table provides contract assets and contract liabilities information from contracts with customers: (In millions) September 30, 2024 December 31, 2023 Contract assets $ 433 $ 357 Contract liabilities $ 864 $ 869

Per Share Data (Tables)

Per Share Data (Tables)	9 Months Ended
	Sep. 30, 2024
Earnings Per Share [Abstract]
Schedule of Basic and Diluted EPS Calculation	Basic and Diluted EPS Calculation Three Months Ended Nine Months Ended (In millions, except per share data) 2024 2023 2024 2023 Net income before non-controlling interests $ 752 $ 738 $ 3,316 $ 3,037 Less: Net income attributable to non-controlling interests 5 8 44 37 Net income attributable to the Company $ 747 $ 730 $ 3,272 $ 3,000 Basic weighted average common shares outstanding 492 494 492 494 Dilutive effect of potentially issuable common shares 4 5 4 5 Diluted weighted average common shares outstanding 496 499 496 499 Average stock price used to calculate common stock equivalents $ 222.13 $ 191.66 $ 209.06 $ 178.64

Supplemental Disclosures to t_2

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Tables)	9 Months Ended
	Sep. 30, 2024
Supplemental Cash Flow Information [Abstract]
Schedule of Additional Information Concerning Acquisitions, Interest and Income Taxes Paid	The following table provides additional information concerning acquisitions, interest and income taxes paid for the nine months ended September 30, 2024 and 2023: (In millions) 2024 2023 Assets acquired, excluding cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity $ 1,310 $ 760 Fiduciary liabilities assumed (8) (14) Liabilities assumed (84) (98) Contingent/deferred purchase consideration (176) (29) Net cash outflow for acquisitions $ 1,042 $ 619 (In millions) 2024 2023 Interest paid $ 538 $ 427 Income taxes paid, net of refunds $ 922 $ 699 The following amounts are included in the consolidated statements of cash flows as operating and financing activities: For the Nine Months Ended September 30, (In millions) 2024 2023 Operating: Contingent consideration payments for prior year acquisitions $ (90) $ (41) Receipt of contingent consideration for dispositions — 1 Acquisition/disposition related net charges for adjustments 21 21 Adjustments and payments related to contingent consideration $ (69) $ (19) Financing: Contingent consideration for prior year acquisitions $ (73) $ (135) Deferred consideration related to prior year acquisitions (18) (52) Payments of deferred and contingent consideration for acquisitions $ (91) $ (187) Receipts of contingent consideration for dispositions $ 1 $ 2

Other Comprehensive (Loss) In_2

Other Comprehensive (Loss) Income (Tables)	9 Months Ended
	Sep. 30, 2024
Equity [Abstract]
Schedule of Accumulated Other Comprehensive (Loss) Income	The changes, net of tax, in the balances of each component of AOCI for the three and nine months ended September 30, 2024 and 2023, including amounts reclassified out of AOCI, are as follows: (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at July 1, 2024 $ (3,050) $ (2,477) $ (5,527) Other comprehensive (loss) income before reclassifications (135) 668 533 Amounts reclassified from accumulated other comprehensive income 4 — 4 Net current period other comprehensive (loss) income (131) 668 537 Balance at September 30, 2024 (a) $ (3,181) $ (1,809) $ (4,990) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at July 1, 2023 $ (2,811) $ (2,244) $ (5,055) Other comprehensive income (loss) before reclassifications 76 (485) (409) Amounts reclassified from accumulated other comprehensive income 4 — 4 Net current period other comprehensive income (loss) 80 (485) (405) Balance at September 30, 2023 (a) $ (2,731) $ (2,729) $ (5,460) (a) At September 30, 2024 and 2023, balances are net of deferred tax assets in pension and post-retirement plans gains (losses) of $1.5 billion and $1.3 billion, respectively. (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at January 1, 2024 $ (3,101) $ (2,194) $ (5,295) Other comprehensive (loss) income before reclassifications (93) 385 292 Amounts reclassified from accumulated other comprehensive income 13 — 13 Net current period other comprehensive (loss) income (80) 385 305 Balance at September 30, 2024 (a) $ (3,181) $ (1,809) $ (4,990) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Adjustments Total Balance at January 1, 2023 $ (2,721) $ (2,593) $ (5,314) Other comprehensive (loss) income before reclassifications (20) (136) (156) Amounts reclassified from accumulated other comprehensive income 10 — 10 Net current period other comprehensive (loss) income (10) (136) (146) Balance at September 30, 2023 (a) $ (2,731) $ (2,729) $ (5,460) (a) At September 30, 2024 and 2023, balances are net of deferred tax assets in pension and post-retirement plans gains (losses) of $1.5 billion and $1.3 billion, respectively.
Schedule of Components of Other Comprehensive (Loss) Income	The components of other comprehensive (loss) income for the three and nine months ended September 30, 2024 and 2023 are as follows: Three Months Ended September 30, 2024 2023 (In millions) Pre-Tax Tax Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 661 $ (7) $ 668 $ (473) $ 12 $ (485) Pension/post-retirement plans: Amortization of (gains) losses included in net benefit (credit) cost: Net actuarial losses (a) 6 2 4 5 1 4 Subtotal 6 2 4 5 1 4 Foreign currency translation adjustments (180) (44) (136) 102 26 76 Effect of settlement 1 — 1 — — — Pension/post-retirement plans (losses) gains (173) (42) (131) 107 27 80 Other comprehensive income (loss) $ 488 $ (49) $ 537 $ (366) $ 39 $ (405) (a) Included in other net benefit credits in the consolidated statements of income. Income tax expense on net actuarial losses are included in income tax expense. Nine Months Ended September 30, 2024 2023 (In millions) Pre-Tax Tax Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 389 $ 4 $ 385 $ (131) $ 5 $ (136) Pension/post-retirement plans: Amortization of (gains) losses included in net benefit (credit) cost: Prior service credits (a) (1) — (1) (1) — (1) Net actuarial losses (a) 19 5 14 15 4 11 Subtotal 18 5 13 14 4 10 Foreign currency translation adjustments (124) (30) (94) (20) (5) (15) Effect of settlement 1 — 1 — — — Other adjustments — — — (7) (2) (5) Pension/post-retirement plans (losses) gains (105) (25) (80) (13) (3) (10) Other comprehensive income (loss) $ 284 $ (21) $ 305 $ (144) $ 2 $ (146) (a) Included in other net benefit credits in the consolidated statements of income. Income tax expense on net actuarial losses are included in income tax expense.

Acquisitions and Dispositions (

Acquisitions and Dispositions (Tables)	9 Months Ended
	Sep. 30, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Schedule for Allocation of Acquisition Costs	The following table presents the preliminary allocation of purchase consideration to the assets acquired and liabilities assumed in 2024, based on the estimated fair values for the acquisitions as of their respective acquisition dates. Amounts in the table primarily reflect the impact of the Horton Group and FBBI acquisitions. Acquisitions through September 30, 2024 (In millions) Cash $ 1,078 Estimated fair value of deferred/contingent purchase consideration 176 Total consideration $ 1,254 Allocation of purchase price: Cash and cash equivalents $ 28 Cash and cash equivalents held in a fiduciary capacity 8 Net receivables 67 Other current assets 30 Goodwill 826 Other intangible assets 371 Fixed assets, net 5 Right of use assets 9 Other assets 2 Total assets acquired 1,346 Current liabilities 29 Fiduciary liabilities 8 Other liabilities 55 Total liabilities assumed 92 Net assets acquired $ 1,254
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	The following table provides information about other intangible assets acquired in 2024: Other intangible assets through September 30, 2024 (In millions) Amount Weighted Average Amortization Period Client relationships $ 349 12.3 years Other 22 2.8 years Total other intangible assets $ 371
Schedule of Pro-Forma Information	The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company in 2024 and 2023. In accordance with accounting guidance related to pro-forma disclosures, the information presented for acquisitions made in 2024 is as if they occurred on January 1, 2023, and reflects acquisitions made in 2023, as if they occurred on January 1, 2022. The unaudited pro-forma information includes the effects of amortization of acquired intangibles in all years. The unaudited pro-forma financial data is presented for illustrative purposes only and is not necessarily indicative of the operating results that would have been achieved if such acquisitions had occurred on the dates indicated, nor is it necessarily indicative of future consolidated results. Three Months Ended Nine Months Ended (In millions, except per share data) 2024 2023 2024 2023 Revenue $ 5,707 $ 5,494 $ 18,535 $ 17,621 Net income attributable to the Company $ 755 $ 749 $ 3,309 $ 3,065 Basic net income per share attributable to the Company $ 1.54 $ 1.52 $ 6.73 $ 6.20 Diluted net income per share attributable to the Company $ 1.52 $ 1.50 $ 6.67 $ 6.14

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	9 Months Ended
	Sep. 30, 2024
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Changes in the Carrying Amount of Goodwill	Changes in the carrying amount of goodwill are as follows: (In millions) 2024 2023 Balance at January 1, $ 17,231 $ 16,251 Goodwill acquired 826 480 Other adjustments (a) 178 (76) Balance at September 30, $ 18,235 $ 16,655 (a) Primarily reflects the impact of foreign exchange.
Schedule of Amortized Intangible Assets	The gross cost and accumulated amortization of other identified intangible assets at September 30, 2024 and December 31, 2023 are as follows: September 30, 2024 December 31, 2023 (In millions) Gross Accumulated Net Gross Accumulated Net Client relationships $ 4,614 $ 1,937 $ 2,677 $ 4,337 $ 1,761 $ 2,576 Other (a) 386 343 43 391 337 54 Other intangible assets $ 5,000 $ 2,280 $ 2,720 $ 4,728 $ 2,098 $ 2,630 (a) Primarily reflects non-compete agreements, trade names and developed technology.
Schedule of Estimated Future Aggregate Amortization Expense	The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2024 (excludes amortization through September 30, 2024) $ 91 2025 337 2026 317 2027 308 2028 285 Subsequent years 1,382 Total future amortization $ 2,720

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2024
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis at September 30, 2024 and December 31, 2023: Identical Assets Observable Inputs Unobservable Inputs Total (In millions) 09/30/24 12/31/23 09/30/24 12/31/23 09/30/24 12/31/23 09/30/24 12/31/23 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 8 $ 5 $ — $ — $ — $ — $ 8 $ 5 Mutual funds (a) 189 178 — — — — 189 178 Money market funds (b) 440 606 — — — — 440 606 Contingent purchase consideration assets (c) — — — — — 1 — 1 Total assets measured at fair value $ 637 $ 789 $ — $ — $ — $ 1 $ 637 $ 790 Fiduciary Assets: Money market funds $ 66 $ 180 $ — $ — $ — $ — $ 66 $ 180 Total fiduciary assets measured $ 66 $ 180 $ — $ — $ — $ — $ 66 $ 180 Liabilities: Contingent purchase consideration liabilities (d) $ — $ — $ — $ — $ 168 $ 252 $ 168 $ 252 Total liabilities measured at fair value $ — $ — $ — $ — $ 168 $ 252 $ 168 $ 252 (a) Included in other assets in the consolidated balance sheets. (b) Included in cash and cash equivalents in the consolidated balance sheets. (c) Included in other receivables in the consolidated balance sheets. (d) Included in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.
Schedule of Changes in Fair Value of Level 3 Liabilities Representing Acquisition Related Contingent Consideration	The following table sets forth a summary of the changes in fair value of the Company’s Level 3 liabilities for the three and nine months ended September 30, 2024 and 2023: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Balance at beginning of period $ 121 $ 223 $ 252 $ 377 Net additions 43 5 60 9 Payments (2) (1) (163) (176) Revaluation impact 6 4 21 21 Other — — (2) — Balance at end of period $ 168 $ 231 $ 168 $ 231

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2024
Leases [Abstract]
Schedule of Lease Cost and Additional Information	The following table provides additional information about the Company’s property leases: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Lease Cost: Operating lease cost (a) $ 84 $ 82 $ 247 $ 243 Short-term lease cost 1 1 4 4 Variable lease cost 31 31 85 94 Sublease income (2) (2) (10) (8) Net lease cost $ 114 $ 112 $ 326 $ 333 Other information: Operating cash outflows from operating leases $ 278 $ 284 Right of use assets obtained in exchange for new operating lease liabilities $ 135 $ 177 Weighted average remaining lease term – real estate 7.8 years 8.1 years Weighted average discount rate – real estate leases 3.64 % 3.28 % (a) Excludes ROU asset impairment charges.
Schedule of Future Minimum Lease Payments for Operating Leases	Future minimum lease payments for the Company’s operating leases at September 30, 2024 are as follows: (In millions) Real Estate Leases 2024 (excludes payments through September 30, 2024) $ 95 2025 371 2026 343 2027 305 2028 229 2029 183 Subsequent years 678 Total future lease payments 2,204 Less: Imputed interest (273) Total $ 1,931 Current lease liabilities $ 313 Long-term lease liabilities 1,618 Total lease liabilities $ 1,931 Note: The above table excludes obligations for leases with original terms of 12 months or less which have not been recognized as a ROU asset or liability in the consolidated balance sheets.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2024
Retirement Benefits [Abstract]
Schedule of Weighted Average Actuarial Assumptions Utilized to Calculate the Net Periodic Benefit Costs	The weighted average actuarial assumptions utilized to calculate the net periodic benefit costs for the U.S. and significant non-U.S. defined benefit plans are as follows: Combined U.S. and significant non-U.S. Plans Pension Benefits September 30, 2024 2023 Weighted average assumptions: Expected return on plan assets 5.44 % 5.31 % Discount rate 4.95 % 5.16 % Rate of compensation increase * 3.16 % 3.16 % (*) There are no rate of compensation increase assumptions for the U.S. defined benefit plans since future benefit accruals were discontinued for those plans after December 31, 2016 and earned benefits are not subject to final salary level adjustments.
Schedule of Net Benefit Costs	The components of the net benefit credit for defined benefit plans are as follows: Combined U.S. and significant non-U.S. Plans For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 5 $ 7 Interest cost 146 151 Expected return on plan assets (222) (218) Recognized actuarial loss 8 5 Net periodic benefit credit $ (63) $ (55) Settlement loss 1 — Net benefit credit $ (62) $ (55) Combined U.S. and significant non-U.S. Plans For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 17 $ 18 Interest cost 434 449 Expected return on plan assets (657) (645) Amortization of prior service cost 1 — Recognized actuarial loss 23 16 Net periodic benefit credit $ (182) $ (162) Settlement loss 1 — Net benefit credit $ (181) $ (162) The following tables provide the amounts reported in the consolidated statements of income: Combined U.S. and significant non-U.S. Plans For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Compensation and benefits expense $ 5 $ 7 Other net benefit credits (67) (62) Net benefit credit $ (62) $ (55) Combined U.S. and significant non-U.S. Plans For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Compensation and benefits expense $ 17 $ 18 Other net benefit credits (198) (180) Net benefit credit $ (181) $ (162) The components of the net benefit credit for the U.S. defined benefit plans are as follows: U.S. Plans only For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Interest cost $ 62 $ 65 Expected return on plan assets (76) (78) Recognized actuarial loss 5 5 Net benefit credit $ (9) $ (8) U.S. Plans only For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Interest cost $ 187 $ 195 Expected return on plan assets (227) (233) Recognized actuarial loss 15 14 Net benefit credit $ (25) $ (24) The components of the net benefit credit for the non-U.S. defined benefit plans are as follows: Significant non-U.S. Plans only For the Three Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 5 $ 7 Interest cost 84 86 Expected return on plan assets (146) (140) Recognized actuarial loss 3 — Net periodic benefit credit $ (54) $ (47) Settlement loss 1 — Net benefit credit $ (53) $ (47) Significant non-U.S. Plans only For the Nine Months Ended September 30, Pension Benefits (In millions) 2024 2023 Service cost $ 17 $ 18 Interest cost 247 254 Expected return on plan assets (430) (412) Amortization of prior service cost 1 — Recognized actuarial loss 8 2 Net periodic benefit credit $ (157) $ (138) Settlement loss 1 — Net benefit credit $ (156) $ (138)

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2024
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	The Company’s outstanding debt is as follows: (In millions) September 30, December 31, 2023 Short-term: Current portion of long-term debt $ 518 $ 1,619 $ 518 $ 1,619 Long-term: Senior notes – 3.50% due 2024 $ — $ 600 Senior notes – 3.875% due 2024 — 1,000 Senior notes – 3.50% due 2025 500 499 Senior notes – 1.349% due 2026 623 617 Senior notes – 3.75% due 2026 599 599 Senior notes – 4.375% due 2029 1,499 1,499 Senior notes – 1.979% due 2030 603 601 Senior notes – 2.25% due 2030 742 741 Senior notes – 2.375% due 2031 397 397 Senior notes – 5.750% due 2032 493 493 Senior notes – 5.875% due 2033 298 298 Senior notes – 5.400% due 2033 593 592 Senior notes – 5.150% due 2034 495 — Senior notes – 4.75% due 2039 496 496 Senior notes – 4.35% due 2047 494 494 Senior notes – 4.20% due 2048 593 593 Senior notes – 4.90% due 2049 1,239 1,239 Senior notes – 2.90% due 2051 346 346 Senior notes – 6.25% due 2052 491 491 Senior notes – 5.450% due 2053 591 591 Senior notes – 5.700% due 2053 988 988 Senior notes – 5.450% due 2054 493 — Mortgage – 5.70% due 2035 271 284 Other 4 5 12,848 13,463 Less: current portion 518 1,619 $ 12,330 $ 11,844
Schedule of Estimated Fair Value of Significant Financial Instruments	The fair value amounts shown in the following table are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or need to dispose of the financial instrument. September 30, 2024 December 31, 2023 (In millions) Carrying Fair Carrying Fair Short-term debt $ 518 $ 515 $ 1,619 $ 1,610 Long-term debt $ 12,330 $ 12,279 $ 11,844 $ 11,723

Restructuring Costs (Tables)

Restructuring Costs (Tables)	9 Months Ended
	Sep. 30, 2024
Restructuring and Related Activities [Abstract]
Schedule of Restructuring and Related Costs Incurred	The Company incurred costs related to these initiatives as follows: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Risk and Insurance Services $ 22 $ 26 $ 73 $ 89 Consulting 14 17 30 33 Corporate 18 9 37 48 Total $ 54 $ 52 $ 140 $ 170
Schedule of Restructuring Activities	Details of the restructuring activity from January 1, 2023 through September 30, 2024, are as follows: (In millions) Severance Real Estate Related Costs (a) Information Technology Consulting and Other Outside Services Total Liability at January 1, 2023 $ 88 $ 56 $ — $ 2 $ 146 2023 charges 148 96 15 42 301 Cash payments (147) (69) (13) (42) (271) Non-cash charges — (44) (2) — (46) Liability at December 31, 2023 $ 89 $ 39 $ — $ 2 $ 130 2024 charges 63 41 19 17 140 Cash payments (123) (34) (19) (19) (195) Non-cash charges — (9) — — (9) Liability at September 30, 2024 $ 29 $ 37 $ — $ — $ 66 (a) Includes ROU and fixed asset impairments and other real estate related costs.

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2024
Segment Reporting [Abstract]
Schedule of Selected Information and Details for MMC's Operating Segments	Selected information about the Company’s segments for the three and nine months ended September 30, 2024 and 2023 is as follows: Three Months Ended Nine Months Ended (In millions) Revenue Operating Income/(Loss) Revenue Operating Income/(Loss) 2024 – Risk and Insurance Services $ 3,453 (a) $ 733 $ 11,748 (c) $ 3,595 Consulting 2,262 (b) 462 6,692 (d) 1,304 Total Segments 5,715 1,195 18,440 4,899 Corporate/Eliminations (18) (87) (49) (224) Total Consolidated $ 5,697 $ 1,108 $ 18,391 $ 4,675 2023 – Risk and Insurance Services $ 3,190 (a) $ 640 $ 10,818 (c) $ 3,192 Consulting 2,206 (b) 424 6,409 (d) 1,223 Total Segments 5,396 1,064 17,227 4,415 Corporate/Eliminations (14) (68) (45) (236) Total Consolidated $ 5,382 $ 996 $ 17,182 $ 4,179 (a) Includes interest income on fiduciary funds of $138 million and $131 million in 2024 and 2023, respectively, and equity method income of $7 million and $3 million in 2024 and 2023, respectively. (b) Includes inter-segment revenue of $18 million and $14 million in 2024 and 2023, respectively. (c) Includes inter-segment revenue of $5 million in both 2024 and 2023, interest income on fiduciary funds of $385 million and $330 million in 2024 and 2023, respectively, and equity method income of $17 million and $14 million in 2024 and 2023, respectively. (d) Includes inter-segment revenue of $44 million and $40 million in 2024 and 2023, respectively. Revenue in 2024 also includes a net gain of $21 million from the sale of Mercer's U.K. pension administration and U.S. health and benefits administration businesses.
Schedule of Details of Operating Segment Revenue	Details of operating segment revenue for the three and nine months ended September 30, 2024 and 2023 are as follows: Three Months Ended Nine Months Ended (In millions) 2024 2023 2024 2023 Risk and Insurance Services Marsh $ 3,023 $ 2,782 $ 9,446 $ 8,685 Guy Carpenter 430 408 2,302 2,133 Total Risk and Insurance Services 3,453 3,190 11,748 10,818 Consulting Mercer 1,452 1,425 4,256 4,143 Oliver Wyman Group 810 781 2,436 2,266 Total Consulting 2,262 2,206 6,692 6,409 Total Segments 5,715 5,396 18,440 17,227 Corporate Eliminations (18) (14) (49) (45) Total $ 5,697 $ 5,382 $ 18,391 $ 17,182

Nature of Operations (Details)

Nature of Operations (Details)	9 Months Ended
	Sep. 30, 2024 segment
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of business segments (segment)	2

Principles of Consolidation a_3

Principles of Consolidation and Other Matters (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 507		$ 507		$ 486
Equity method investments lag period (in months)			3 months
Net investment income	$ 1	$ 1	$ 3	$ 6
Effective tax rate (as a percent)	27.30%	20.60%	25.80%	23.70%
Share-based payments of excess tax benefit (as a percent)	0.30%	1%	1.30%	1.20%
Valuation allowance		$ 48
Effective tax rate due to change in enacted income tax rate (as a percent)		4.80%		1.10%
Unrecognized tax benefits	$ 122		$ 122		$ 124
Reasonably possible decrease in unrecognized tax benefits	$ 66		$ 66

Revenue (Narrative) (Details)

Revenue (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Revenue from Contract with Customer [Abstract]
Threshold percentage of total revenue (as a percent)			1%
Revenue recognized that was included in the contract liability balance at the beginning of the period	$ 149	$ 187	$ 730	$ 698
Performance obligation satisfied in previous period	$ 18	$ 20	$ 61	$ 64

Revenue (Disaggregation of Reve

Revenue (Disaggregation of Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Disaggregation of Revenue [Line Items]
Revenue	$ 5,697	$ 5,382	$ 18,391	$ 17,182
Total Segments
Disaggregation of Revenue [Line Items]
Revenue	5,715	5,396	18,440	17,227
Risk and Insurance Services | Total Segments
Disaggregation of Revenue [Line Items]
Fiduciary interest income	138	131	385	330
Revenue	3,453	3,190	11,748	10,818
Risk and Insurance Services | Subtotal | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	3,315	3,059	11,363	10,488
Risk and Insurance Services | Total Marsh | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	2,934	2,700	9,202	8,482
Risk and Insurance Services | Guy Carpenter | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	381	359	2,161	2,006
Risk and Insurance Services | Total International | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	1,223	1,137	4,149	3,848
Risk and Insurance Services | EMEA | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	747	692	2,684	2,482
Risk and Insurance Services | Asia Pacific | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	342	311	1,069	980
Risk and Insurance Services | Latin America | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	134	134	396	386
Risk and Insurance Services | U.S./Canada | Total Segments
Disaggregation of Revenue [Line Items]
Revenue, excluding fiduciary interest income	1,711	1,563	5,053	4,634
Consulting | Total Segments
Disaggregation of Revenue [Line Items]
Revenue	2,262	2,206	6,692	6,409
Consulting | Mercer | Total Segments
Disaggregation of Revenue [Line Items]
Revenue	1,452	1,425	4,256	4,143
Consulting | Mercer | Wealth | Total Segments
Disaggregation of Revenue [Line Items]
Revenue	625	635	1,909	1,853
Consulting | Mercer | Health | Total Segments
Disaggregation of Revenue [Line Items]
Revenue	520	496	1,605	1,559
Consulting | Mercer | Career | Total Segments
Disaggregation of Revenue [Line Items]
Revenue	307	294	742	731
Consulting | Oliver Wyman Group | Total Segments
Disaggregation of Revenue [Line Items]
Revenue	$ 810	$ 781	$ 2,436	$ 2,266

Revenue (Contract Assets and Li

Revenue (Contract Assets and Liabilities) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Revenue from Contract with Customer [Abstract]
Contract assets	$ 433	$ 357
Contract liabilities	$ 864	$ 869

Fiduciary Assets and Liabilit_2

Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 15,600		$ 15,600		$ 13,800
Total Segments | Risk and Insurance Services
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	$ 138	$ 131	$ 385	$ 330

Per Share Data (Details)

Per Share Data (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Earnings Per Share [Abstract]
Net income before non-controlling interests	$ 752	$ 738	$ 3,316	$ 3,037
Less: Net income attributable to non-controlling interests	5	8	44	37
Net income attributable to the Company	$ 747	$ 730	$ 3,272	$ 3,000
Basic weighted average common shares outstanding (in shares)	492	494	492	494
Dilutive effect of potentially issuable common shares (in shares)	4	5	4	5
Diluted weighted average common shares outstanding (in shares)	496	499	496	499
Average stock price used to calculate common stock equivalents (in dollars per share)	$ 222.13	$ 191.66	$ 209.06	$ 178.64

Supplemental Disclosures to t_3

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Additional Information Concerning Acquisitions, Interest and Income Taxes Paid) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Supplemental Cash Flow Information [Abstract]
Assets acquired, excluding cash, cash equivalents, and cash and cash equivalents held in a fiduciary capacity	$ 1,310	$ 760
Fiduciary liabilities assumed	(8)	(14)
Liabilities assumed	(84)	(98)
Contingent/deferred purchase consideration	(176)	(29)
Net cash outflow for acquisitions	1,042	619
Interest paid	538	427
Income taxes paid, net of refunds	$ 922	$ 699

Supplemental Disclosures to t_4

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Supplemental Operating and Financing Cash Flow Items) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Operating:
Contingent consideration payments for prior year acquisitions	$ (90)	$ (41)
Receipt of contingent consideration for dispositions	0	1
Acquisition/disposition related net charges for adjustments	21	21
Adjustments and payments related to contingent consideration	(69)	(19)
Financing:
Contingent consideration for prior year acquisitions	(73)	(135)
Deferred consideration related to prior year acquisitions	(18)	(52)
Payments of deferred and contingent consideration for acquisitions	(91)	(187)
Receipts of contingent consideration for dispositions	$ 1	$ 2

Supplemental Disclosures to t_5

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Supplemental Cash Flow Information [Abstract]
Non-cash issuance of common stock			$ 328	$ 304
Stock-based compensation expense, equity awards	$ 90	$ 82	$ 283	$ 273

Other Comprehensive (Loss) In_3

Other Comprehensive (Loss) Income (Accumulated Other Comprehensive (Loss) Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			$ 12,370
Other comprehensive income (loss), net of tax	$ 537	$ (405)	305	$ (146)
Balance, end of period	13,882	11,586	13,882	11,586
Total
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(5,527)	(5,055)	(5,295)	(5,314)
Other comprehensive (loss) income before reclassifications	533	(409)	292	(156)
Amounts reclassified from accumulated other comprehensive income	4	4	13	10
Other comprehensive income (loss), net of tax	537	(405)	305	(146)
Balance, end of period	(4,990)	(5,460)	(4,990)	(5,460)
Pension/Post-Retirement Plans Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(3,050)	(2,811)	(3,101)	(2,721)
Other comprehensive (loss) income before reclassifications	(135)	76	(93)	(20)
Amounts reclassified from accumulated other comprehensive income	4	4	13	10
Other comprehensive income (loss), net of tax	(131)	80	(80)	(10)
Balance, end of period	(3,181)	(2,731)	(3,181)	(2,731)
Deferred tax assets, net	1,500	1,300	1,500	1,300
Foreign Currency Translation Adjustments
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(2,477)	(2,244)	(2,194)	(2,593)
Other comprehensive (loss) income before reclassifications	668	(485)	385	(136)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	668	(485)	385	(136)
Balance, end of period	$ (1,809)	$ (2,729)	$ (1,809)	$ (2,729)

Other Comprehensive (Loss) In_4

Other Comprehensive (Loss) Income (Components of Other Comprehensive (Loss) Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pre-Tax
Other comprehensive income (loss)	$ 488	$ (366)	$ 284	$ (144)
Tax
Other comprehensive income (loss)	(49)	39	(21)	2
Net of Tax
Other comprehensive income (loss), net of tax	537	(405)	305	(146)
Foreign currency translation adjustments
Pre-Tax
Other comprehensive income (loss), before reclassification	661	(473)	389	(131)
Tax
Other comprehensive income (loss), before reclassification	(7)	12	4	5
Net of Tax
Other comprehensive income (loss), before reclassification	668	(485)	385	(136)
Reclassification from AOCI	0	0	0	0
Other comprehensive income (loss), net of tax	668	(485)	385	(136)
Prior service credits
Pre-Tax
Reclassification from AOCI			(1)	(1)
Tax
Reclassification from AOCI			0	0
Net of Tax
Reclassification from AOCI			(1)	(1)
Net actuarial losses
Pre-Tax
Reclassification from AOCI	6	5	19	15
Tax
Reclassification from AOCI	2	1	5	4
Net of Tax
Reclassification from AOCI	4	4	14	11
Pension/post-retirement plans (losses) gains
Pre-Tax
Reclassification from AOCI	6	5	18	14
Other comprehensive income (loss)	(173)	107	(105)	(13)
Tax
Reclassification from AOCI	2	1	5	4
Other comprehensive income (loss)	(42)	27	(25)	(3)
Net of Tax
Other comprehensive income (loss), before reclassification	(135)	76	(93)	(20)
Reclassification from AOCI	4	4	13	10
Other comprehensive income (loss), net of tax	(131)	80	(80)	(10)
Foreign currency translation adjustments
Pre-Tax
Other comprehensive income (loss), before reclassification	(180)	102	(124)	(20)
Tax
Other comprehensive income (loss), before reclassification	(44)	26	(30)	(5)
Net of Tax
Other comprehensive income (loss), before reclassification	(136)	76	(94)	(15)
Effect of settlement
Pre-Tax
Other comprehensive income (loss), before reclassification	1	0	1	0
Tax
Other comprehensive income (loss), before reclassification	0	0	0	0
Net of Tax
Other comprehensive income (loss), before reclassification	$ 1	$ 0	1	0
Other adjustments
Pre-Tax
Other comprehensive income (loss), before reclassification			0	(7)
Tax
Other comprehensive income (loss), before reclassification			0	(2)
Net of Tax
Other comprehensive income (loss), before reclassification			$ 0	$ (5)

Acquisitions and Dispositions_2

Acquisitions and Dispositions (Narrative) (Details) $ in Millions			3 Months Ended					9 Months Ended		12 Months Ended
	Sep. 30, 2024 USD ($)	Jan. 01, 2024 USD ($)	Sep. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Sep. 30, 2023 USD ($)	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2024 USD ($) acquisition	Sep. 30, 2023 USD ($)	Dec. 31, 2023 acquisition	Dec. 31, 2024 USD ($)
Business Acquisition [Line Items]
Total consideration								$ 1,300	$ 711
Cash paid								1,100	682
Estimated fair value of deferred/contingent purchase consideration								176	29
Deferred purchase consideration from prior years' acquisitions								18	52
Contingent consideration from prior year's acquisitions								73	135
Cash divested from deconsolidation							$ 20
Purchase of non-controlling interests						$ 139		5	139
Total Segments | Small Individual Financial Advisory Business
Business Acquisition [Line Items]
Net gain (loss) on disposition of business									(17)
Discontinued Operations, Disposed of by Sale | U.S. Health And Benefits And U.K Pension Administration Businesses
Business Acquisition [Line Items]
Cash proceeds from sale		$ 114
Net gain (loss) on disposition of business		$ 21
Exit costs				$ 18
Discontinued Operations, Disposed of by Sale | U.S. Health And Benefits And U.K Pension Administration Businesses | Total Segments
Business Acquisition [Line Items]
Net gain (loss) on disposition of business								21
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions									52
Contingent consideration from prior year's acquisitions								163	176
Pro forma revenue					$ 50				91
Operating income (loss) related to acquisitions					5				14
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration								1,254
Cash paid								1,078
Estimated fair value of deferred/contingent purchase consideration								176
Pro forma revenue			$ 82					144
Operating income (loss) related to acquisitions			(2)					(5)
Westpac Transaction
Business Acquisition [Line Items]
Acquisition related costs			$ 20		$ 5			$ 49	$ 32
McGriff Insurance Services, LLC
Business Acquisition [Line Items]
Price of acquisition, expected	$ 7,750
McGriff Insurance Services, LLC | Forecast
Business Acquisition [Line Items]
Deferred tax assets											$ 500
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)								2 years	2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)								4 years	4 years
Risk and Insurance Services
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition								8		9
Consulting
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition								5		5

Acquisitions and Dispositions_3

Acquisitions and Dispositions (Allocation of Acquisition Costs) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Business Acquisition [Line Items]
Cash	$ 1,100	$ 682
Estimated fair value of deferred/contingent purchase consideration	176	29
Total consideration	1,300	711
Allocation of purchase price:
Goodwill	18,235	$ 16,655	$ 17,231	$ 16,251
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	1,078
Estimated fair value of deferred/contingent purchase consideration	176
Total consideration	1,254
Allocation of purchase price:
Cash and cash equivalents	28
Cash and cash equivalents held in a fiduciary capacity	8
Net receivables	67
Other current assets	30
Goodwill	826
Other intangible assets	371
Fixed assets, net	5
Right of use assets	9
Other assets	2
Total assets acquired	1,346
Current liabilities	29
Fiduciary liabilities	8
Other liabilities	55
Total liabilities assumed	92
Net assets acquired	$ 1,254

Acquisitions and Dispositions_4

Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2024 USD ($)
Finite-Lived Intangible Assets [Line Items]
Amount	$ 371
Client relationships
Finite-Lived Intangible Assets [Line Items]
Amount	$ 349
Weighted Average Amortization Period	12 years 3 months 18 days
Other
Finite-Lived Intangible Assets [Line Items]
Amount	$ 22
Weighted Average Amortization Period	2 years 9 months 18 days

Acquisitions and Dispositions_5

Acquisitions and Dispositions (Pro-Forma Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Revenue	$ 5,707	$ 5,494	$ 18,535	$ 17,621
Net income attributable to the Company	$ 755	$ 749	$ 3,309	$ 3,065
Basic net income per share attributable to the Company (in dollars per share)	$ 1.54	$ 1.52	$ 6.73	$ 6.20
Diluted net income per share attributable to the Company (in dollars per share)	$ 1.52	$ 1.50	$ 6.67	$ 6.14

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Dec. 31, 2022
Segment Reporting Information [Line Items]
Goodwill, impairment loss	$ 0
Indefinite-lived intangible assets	0		$ 0		$ 0
Goodwill	18,235,000,000	$ 16,655,000,000	18,235,000,000	$ 16,655,000,000	$ 17,231,000,000	$ 16,251,000,000
Aggregate amortization expense	90,000,000	$ 85,000,000	269,000,000	$ 257,000,000
Risk and Insurance Services
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	263,000,000		263,000,000
Goodwill	14,000,000,000		14,000,000,000
Consulting
Segment Reporting Information [Line Items]
Goodwill expected to be tax deductible	88,000,000		88,000,000
Goodwill	$ 4,200,000,000		$ 4,200,000,000

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Goodwill [Roll Forward]
Balance at January 1,	$ 17,231	$ 16,251
Goodwill acquired	826	480
Other adjustments	178	(76)
Balance at September 30,	$ 18,235	$ 16,655

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Finite-Lived Intangible Assets [Line Items]
Gross Cost	$ 5,000	$ 4,728
Accumulated Amortization	2,280	2,098
Net Carrying Amount	2,720	2,630
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost	4,614	4,337
Accumulated Amortization	1,937	1,761
Net Carrying Amount	2,677	2,576
Other
Finite-Lived Intangible Assets [Line Items]
Gross Cost	386	391
Accumulated Amortization	343	337
Net Carrying Amount	$ 43	$ 54

Goodwill And Other Intangible_5

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Goodwill and Intangible Assets Disclosure [Abstract]
2024 (excludes amortization through September 30, 2024)	$ 91
2025	337
2026	317
2027	308
2028	285
Subsequent years	1,382
Net Carrying Amount	$ 2,720	$ 2,630

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment	$ 275		$ 266
Equity securities	19		16
Equity investments without readily determinable market value	21		20
Private Insurance and Consulting
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment	74		63
Private Equity Investments
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment	201		203
Commitments for potential future investments	120
Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity securities	8		5
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from contingent purchase consideration, asset	1
Equity securities	$ 0		$ 0
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period (in years)	2 years	2 years
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period (in years)	4 years	4 years

Fair Value Measurements (Assets

Fair Value Measurements (Assets and Liabilities Measured at Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Financial instruments owned:
Exchange traded equity securities	$ 19	$ 16
Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	8	5
Mutual funds	189	178
Money market funds	440	606
Contingent purchase consideration assets	0	1
Total assets measured at fair value	637	790
Fiduciary Assets:
Total fiduciary assets measured at fair value	66	180
Liabilities:
Contingent purchase consideration liabilities	168	252
Total liabilities measured at fair value	168	252
Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	8	5
Mutual funds	189	178
Money market funds	440	606
Contingent purchase consideration assets	0	0
Total assets measured at fair value	637	789
Fiduciary Assets:
Total fiduciary assets measured at fair value	66	180
Liabilities:
Contingent purchase consideration liabilities	0	0
Total liabilities measured at fair value	0	0
Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Money market funds	0	0
Contingent purchase consideration assets	0	0
Total assets measured at fair value	0	0
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Liabilities:
Contingent purchase consideration liabilities	0	0
Total liabilities measured at fair value	0	0
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Money market funds	0	0
Contingent purchase consideration assets	0	1
Total assets measured at fair value	0	1
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Liabilities:
Contingent purchase consideration liabilities	168	252
Total liabilities measured at fair value	168	252
Money market funds | Fair Value, Measurements, Recurring
Fiduciary Assets:
Total fiduciary assets measured at fair value	66	180
Money market funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Total fiduciary assets measured at fair value	66	180
Money market funds | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Total fiduciary assets measured at fair value	0	0
Money market funds | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Total fiduciary assets measured at fair value	$ 0	$ 0

Fair Value Measurements (Change

Fair Value Measurements (Changes in Fair Value Of Level 3 Liabilities Representing Acquisition Related Contingent Consideration) (Details) - Contingent Consideration - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 121	$ 223	$ 252	$ 377
Net additions	43	5	60	9
Payments	(2)	(1)	(163)	(176)
Revaluation impact	6	4	21	21
Other	0	0	(2)	0
Balance at end of period	$ 168	$ 231	$ 168	$ 231

Derivatives (Details)

Derivatives (Details) - 9 months ended Sep. 30, 2024 $ in Millions, € in Billions	USD ($)	EUR (€)
Derivative [Line Items]
Net investment hedge, threshold percentage of the equity balance (as a percent)	80%
Increase in net investment hedges | $	$ 8
Net Investment Hedging
Derivative [Line Items]
Derivative, notional amount | €		€ 1.1

Leases (Narrative) (Details)

Leases (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Lessee, Lease, Description [Line Items]
ROU assets impairment loss	$ 7,000,000	$ 6,000,000	$ 9,000,000	$ 19,000,000
Lessee, operating lease, lease not yet commenced, amount	$ 0		$ 0
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (in years)	10 years		10 years
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (in years)	25 years		25 years

Leases (Lease Cost and Addition

Leases (Lease Cost and Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Leases [Abstract]
Operating lease cost	$ 84	$ 82	$ 247	$ 243
Short-term lease cost	1	1	4	4
Variable lease cost	31	31	85	94
Sublease income	(2)	(2)	(10)	(8)
Net lease cost	$ 114	$ 112	326	333
Operating cash outflows from operating leases			278	284
Right of use assets obtained in exchange for new operating lease liabilities			$ 135	$ 177
Weighted average remaining lease term – real estate	7 years 9 months 18 days	8 years 1 month 6 days	7 years 9 months 18 days	8 years 1 month 6 days
Weighted average discount rate – real estate leases	3.64%	3.28%	3.64%	3.28%

Leases (Future Minimum Payments

Leases (Future Minimum Payments for Operating Leases) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Leases [Abstract]
2024 (excludes payments through September 30, 2024)	$ 95
2025	371
2026	343
2027	305
2028	229
2029	183
Subsequent years	678
Total future lease payments	2,204
Less: Imputed interest	(273)
Total	1,931
Current lease liabilities	313	$ 312
Long-term lease liabilities	$ 1,618	$ 1,661

Retirement Benefits (Weighted A

Retirement Benefits (Weighted Average Actuarial Assumptions Utilized to Calculate the Net Periodic Benefit Costs) (Details) - Pension Benefits	9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023
Weighted average assumptions:
Expected return on plan assets	5.44%	5.31%
Discount rate	4.95%	5.16%
United States
Weighted average assumptions:
Rate of compensation increase	0%	0%
Foreign Plan
Weighted average assumptions:
Rate of compensation increase	3.16%	3.16%

Retirement Benefits (Narrative)

Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Dec. 31, 2023	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer		$ 16	$ 26	$ 67	$ 73
Estimated future employer contributions in current fiscal year		25		25
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		45	45	142	133
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 39	$ 39	$ 130	$ 120
United Kingdom | Defined Benefit Plan Assets Benchmark | Geographic Concentration Risk
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage (as a percent)	79%
Equity Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		50%		50%
Actual asset allocation percentage of equity (as a percent)		50%		50%
Equity Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		13%		13%
Actual asset allocation percentage of equity (as a percent)		14%		14%
Fixed Income Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		50%		50%
Actual asset allocation percentage of equity (as a percent)		50%		50%
Fixed Income Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage (as a percent)		87%		87%
Actual asset allocation percentage of equity (as a percent)		86%		86%

Retirement Benefits (Defined Be

Retirement Benefits (Defined Benefit Plan Net Periodic Benefit Cost Combined U.S. and Significant Non-U.S. Plans) (Details) - Pension Benefits - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 5	$ 7	$ 17	$ 18
Interest cost	146	151	434	449
Expected return on plan assets	(222)	(218)	(657)	(645)
Amortization of prior service cost			1	0
Recognized actuarial loss	8	5	23	16
Net benefit credit	(63)	(55)	(182)	(162)
Settlement loss	1	0	1	0
Net benefit credit	(62)	(55)	(181)	(162)
United States
Defined Benefit Plan Disclosure [Line Items]
Interest cost	62	65	187	195
Expected return on plan assets	(76)	(78)	(227)	(233)
Recognized actuarial loss	5	5	15	14
Net benefit credit	(9)	(8)	(25)	(24)
Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	7	17	18
Interest cost	84	86	247	254
Expected return on plan assets	(146)	(140)	(430)	(412)
Amortization of prior service cost			1	0
Recognized actuarial loss	3	0	8	2
Net benefit credit	(54)	(47)	(157)	(138)
Settlement loss	1	0	1	0
Net benefit credit	$ (53)	$ (47)	$ (156)	$ (138)

Retirement Benefits (Defined _2

Retirement Benefits (Defined Benefit Plan Net Periodic Benefit Cost Amounts Recorded in Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense	$ (1,108)	$ (996)	$ (4,675)	$ (4,179)
Other net benefit credits	(68)	(62)	(201)	(180)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense	5	7	17	18
Other net benefit credits	(67)	(62)	(198)	(180)
Net benefit credit	$ (62)	$ (55)	$ (181)	$ (162)

Debt (Outstanding Debt) (Detail

Debt (Outstanding Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Jun. 30, 2024	Feb. 29, 2024	Dec. 31, 2023	Sep. 30, 2023	Mar. 31, 2023
Debt Instrument [Line Items]
Current portion of long-term debt	$ 518			$ 1,619
Short-term debt	518			1,619
Long-term debt	12,848			13,463
Long-term debt, net	12,330			11,844
Senior notes – 3.50% due 2024
Debt Instrument [Line Items]
Long-term debt	$ 0			600
Interest rate (as a percent)	3.50%	3.50%
Senior notes – 3.875% due 2024
Debt Instrument [Line Items]
Long-term debt	$ 0			1,000
Interest rate (as a percent)	3.875%
Senior notes – 3.50% due 2025
Debt Instrument [Line Items]
Long-term debt	$ 500			499
Interest rate (as a percent)	3.50%
Senior notes – 1.349% due 2026
Debt Instrument [Line Items]
Long-term debt	$ 623			617
Interest rate (as a percent)	1.349%
Senior notes – 3.75% due 2026
Debt Instrument [Line Items]
Long-term debt	$ 599			599
Interest rate (as a percent)	3.75%
Senior notes – 4.375% due 2029
Debt Instrument [Line Items]
Long-term debt	$ 1,499			1,499
Interest rate (as a percent)	4.375%
Senior notes – 1.979% due 2030
Debt Instrument [Line Items]
Long-term debt	$ 603			601
Interest rate (as a percent)	1.979%
Senior notes – 2.25% due 2030
Debt Instrument [Line Items]
Long-term debt	$ 742			741
Interest rate (as a percent)	2.25%
Senior notes – 2.375% due 2031
Debt Instrument [Line Items]
Long-term debt	$ 397			397
Interest rate (as a percent)	2.375%
Senior notes – 5.750% due 2032
Debt Instrument [Line Items]
Long-term debt	$ 493			493
Interest rate (as a percent)	5.75%
Senior notes – 5.875% due 2033
Debt Instrument [Line Items]
Long-term debt	$ 298			298
Interest rate (as a percent)	5.875%
Senior notes – 5.400% due 2033
Debt Instrument [Line Items]
Long-term debt	$ 593			592
Interest rate (as a percent)	5.40%				5.40%
Senior notes – 5.150% due 2034
Debt Instrument [Line Items]
Long-term debt	$ 495			0
Interest rate (as a percent)	5.15%		5.15%
Senior notes – 4.75% due 2039
Debt Instrument [Line Items]
Long-term debt	$ 496			496
Interest rate (as a percent)	4.75%
Senior notes – 4.35% due 2047
Debt Instrument [Line Items]
Long-term debt	$ 494			494
Interest rate (as a percent)	4.35%
Senior notes – 4.20% due 2048
Debt Instrument [Line Items]
Long-term debt	$ 593			593
Interest rate (as a percent)	4.20%
Senior notes – 4.90% due 2049
Debt Instrument [Line Items]
Long-term debt	$ 1,239			1,239
Interest rate (as a percent)	4.90%
Senior notes – 2.90% due 2051
Debt Instrument [Line Items]
Long-term debt	$ 346			346
Interest rate (as a percent)	2.90%
Senior notes – 6.25% due 2052
Debt Instrument [Line Items]
Long-term debt	$ 491			491
Interest rate (as a percent)	6.25%
Senior notes – 5.450% due 2053
Debt Instrument [Line Items]
Long-term debt	$ 591			591
Interest rate (as a percent)	5.45%					5.45%
Senior notes – 5.700% due 2053
Debt Instrument [Line Items]
Long-term debt	$ 988			988
Interest rate (as a percent)	5.70%				5.70%
Senior notes – 5.450% due 2054
Debt Instrument [Line Items]
Long-term debt	$ 493			0
Interest rate (as a percent)	5.45%		5.45%
Mortgage – 5.70% due 2035
Debt Instrument [Line Items]
Long-term debt	$ 271			284
Interest rate (as a percent)	5.70%
Other
Debt Instrument [Line Items]
Long-term debt	$ 4			$ 5

Debt (Narrative) (Details)

Debt (Narrative) (Details)		1 Months Ended			3 Months Ended	9 Months Ended
	Sep. 29, 2024 USD ($)	Jun. 30, 2024 USD ($)	Mar. 31, 2024 USD ($)	Oct. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2024 USD ($)	Sep. 30, 2023 USD ($)	Feb. 29, 2024 USD ($)	Dec. 31, 2023 USD ($)	Nov. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)
Debt Instrument [Line Items]
Commercial paper outstanding						$ 0			$ 0
Upfront fees						23,000,000	$ 0
Other Debt Facilities
Debt Instrument [Line Items]
Revolving credit facility, amount outstanding						0			0
Other credit and overdraft facilities						124,000,000			113,000,000
Letters of credit						$ 153,000,000			139,000,000
Senior notes – 3.50% due 2024
Debt Instrument [Line Items]
Interest rate (as a percent)		3.50%				3.50%
Senior notes – 3.50% due 2024 | Senior Notes
Debt Instrument [Line Items]
Repayments of debt		$ 600,000,000
3.875% Senior Debt Obligations October 2024
Debt Instrument [Line Items]
Interest rate (as a percent)			3.875%
3.875% Senior Debt Obligations October 2024 | Senior Notes
Debt Instrument [Line Items]
Repayments of debt			$ 1,000,000,000
Senior notes – 5.150% due 2034
Debt Instrument [Line Items]
Interest rate (as a percent)						5.15%		5.15%
Senior notes – 5.150% due 2034 | Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount								$ 500,000,000
Senior notes – 5.450% due 2054
Debt Instrument [Line Items]
Interest rate (as a percent)						5.45%		5.45%
Senior notes – 5.450% due 2054 | Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount								$ 500,000,000
4.05% Senior Debt Obligations October 2023
Debt Instrument [Line Items]
Interest rate (as a percent)				4.05%
4.05% Senior Debt Obligations October 2023 | Senior Notes
Debt Instrument [Line Items]
Repayments of debt				$ 250,000,000
Senior notes – 5.400% due 2033
Debt Instrument [Line Items]
Interest rate (as a percent)					5.40%	5.40%	5.40%
Senior notes – 5.400% due 2033 | Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount					$ 600,000,000		$ 600,000,000
Senior notes – 5.700% due 2053
Debt Instrument [Line Items]
Interest rate (as a percent)					5.70%	5.70%	5.70%
Senior notes – 5.700% due 2053 | Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount					$ 1,000,000,000		$ 1,000,000,000
Senior notes – 5.450% due 2053
Debt Instrument [Line Items]
Interest rate (as a percent)						5.45%					5.45%
Senior notes – 5.450% due 2053 | Senior Notes
Debt Instrument [Line Items]
Debt instrument face amount											$ 600,000,000
Revolving Credit Facility
Debt Instrument [Line Items]
Debt instrument, term (in years)				5 years
Revolving credit facility, borrowing capacity				$ 3,500,000,000
Revolving Credit Facility | New Facility
Debt Instrument [Line Items]
Revolving credit facility, borrowing capacity					2,800,000,000		2,800,000,000
Revolving credit facility, amount outstanding						$ 0			$ 0
Revolving Credit Facility | Uncommitted Credit Facility
Debt Instrument [Line Items]
Debt instrument, term (in years)				1 year
Revolving credit facility, amount outstanding					0		$ 0
Repayments of lines of credit					$ 200,000,000
Debt, weighted average interest rate (as a percent)					5.50%		5.50%
Commercial Paper
Debt Instrument [Line Items]
Short-term debt				$ 2,800,000,000						$ 3,500,000,000
Line of Credit | Bridge Loan Facility
Debt Instrument [Line Items]
Debt instrument, term (in years)	364 days
Revolving credit facility, borrowing capacity	$ 7,750,000,000
Percentage of loans acquired with credit facility (as a percent)	1
Upfront fees	$ 23,000,000

Debt (Estimated Fair Value of S

Debt (Estimated Fair Value of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 518	$ 1,619
Long-term debt	12,330	11,844
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	515	1,610
Long-term debt	$ 12,279	$ 11,723

Restructuring Costs (Narrative)

Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost	$ 650		$ 650
Restructuring and related cost, cost incurred to date	540		540
Costs incurred	54	$ 52	140	$ 170	$ 301
Severance and Lease Exit Charges
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 36		$ 96

Restructuring Costs (Restructur

Restructuring Costs (Restructuring and Related Costs Incurred) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Restructuring Cost and Reserve [Line Items]
Total	$ 54	$ 52	$ 140	$ 170	$ 301
Corporate
Restructuring Cost and Reserve [Line Items]
Total	18	9	37	48
Risk and Insurance Services
Restructuring Cost and Reserve [Line Items]
Total	22	26	73	89
Consulting
Restructuring Cost and Reserve [Line Items]
Total	$ 14	$ 17	$ 30	$ 33

Restructuring Costs (Restruct_2

Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023
Restructuring Reserve [Roll Forward]
Liability at beginning of period			$ 130	$ 146	$ 146
Restructuring charges	$ 54	$ 52	140	170	301
Cash payments			(195)		(271)
Non-cash charges			(9)		(46)
Liability at end of period	66		66		130
Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period			89	88	88
Restructuring charges			63		148
Cash payments			(123)		(147)
Non-cash charges			0		0
Liability at end of period	29		29		89
Real Estate Related Costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period			39	56	56
Restructuring charges			41		96
Cash payments			(34)		(69)
Non-cash charges			(9)		(44)
Liability at end of period	37		37		39
Information Technology
Restructuring Reserve [Roll Forward]
Liability at beginning of period			0	0	0
Restructuring charges			19		15
Cash payments			(19)		(13)
Non-cash charges			0		(2)
Liability at end of period	0		0		0
Consulting and Other Outside Services
Restructuring Reserve [Roll Forward]
Liability at beginning of period			2	$ 2	2
Restructuring charges			17		42
Cash payments			(19)		(42)
Non-cash charges			0		0
Liability at end of period	$ 0		$ 0		$ 2

Common Stock (Details)

Common Stock (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended			3 Months Ended		9 Months Ended
	Aug. 31, 2024	May 31, 2024	Feb. 29, 2024	Sep. 30, 2024	Mar. 31, 2024	Sep. 30, 2024	Sep. 30, 2023
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)							5.1
Purchase of treasury shares						$ 900	$ 900
Stock-based compensation, shares issued during period (in shares)						3.3	3.3
Dividends, per share, cash paid (in dollars per share)	$ 0.815	$ 0.710	$ 0.710
Dividends, per share, payable (in dollars per share)				$ 0.815		$ 0.815
2024 Q1 January Dividends
Equity, Class of Treasury Stock [Line Items]
Dividend per share (in dollars per share)					$ 0.710
2024 Q1 March Dividends
Equity, Class of Treasury Stock [Line Items]
Dividend per share (in dollars per share)					$ 0.710
O 2024 Q2 1 Dividends
Equity, Class of Treasury Stock [Line Items]
Dividend per share (in dollars per share)				0.815
O 2024 Q2 2 Dividends
Equity, Class of Treasury Stock [Line Items]
Dividend per share (in dollars per share)				$ 0.815
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)						4.3
Stock repurchase program, remaining authorized repurchase amount				$ 2,300		$ 2,300

Segment Information (Selected I

Segment Information (Selected Information and Details for MMC's Operating Segments) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
	Jan. 01, 2024	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenue		$ 5,697	$ 5,382	$ 18,391	$ 17,182
Operating Income/(Loss)		1,108	996	4,675	4,179
Discontinued Operations, Disposed of by Sale | U.S. Health And Benefits And U.K Pension Administration Businesses
Segment Reporting Information [Line Items]
Net gain includes in revenue consolidated statements of income	$ 21
Total Segments
Segment Reporting Information [Line Items]
Revenue		5,715	5,396	18,440	17,227
Operating Income/(Loss)		1,195	1,064	4,899	4,415
Total Segments | Discontinued Operations, Disposed of by Sale | U.S. Health And Benefits And U.K Pension Administration Businesses
Segment Reporting Information [Line Items]
Net gain includes in revenue consolidated statements of income				21
Total Segments | Risk and Insurance Services
Segment Reporting Information [Line Items]
Revenue		3,453	3,190	11,748	10,818
Operating Income/(Loss)		733	640	3,595	3,192
Interest on fiduciary funds		138	131	385	330
Equity method investment income (loss)		7	3	17	14
Total Segments | Consulting
Segment Reporting Information [Line Items]
Revenue		2,262	2,206	6,692	6,409
Operating Income/(Loss)		462	424	1,304	1,223
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue		(18)	(14)	(49)	(45)
Operating Income/(Loss)		(87)	(68)	(224)	(236)
Intersegment Eliminations | Risk and Insurance Services
Segment Reporting Information [Line Items]
Revenue				5	5
Intersegment Eliminations | Consulting
Segment Reporting Information [Line Items]
Revenue		$ 18	$ 14	$ 44	$ 40

Segment Information (Details of

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Segment Reporting Information [Line Items]
Revenue	$ 5,697	$ 5,382	$ 18,391	$ 17,182
Total Segments
Segment Reporting Information [Line Items]
Revenue	5,715	5,396	18,440	17,227
Total Segments | Risk and Insurance Services
Segment Reporting Information [Line Items]
Revenue	3,453	3,190	11,748	10,818
Total Segments | Risk and Insurance Services | Marsh
Segment Reporting Information [Line Items]
Revenue	3,023	2,782	9,446	8,685
Total Segments | Risk and Insurance Services | Guy Carpenter
Segment Reporting Information [Line Items]
Revenue	430	408	2,302	2,133
Total Segments | Consulting
Segment Reporting Information [Line Items]
Revenue	2,262	2,206	6,692	6,409
Total Segments | Consulting | Mercer
Segment Reporting Information [Line Items]
Revenue	1,452	1,425	4,256	4,143
Total Segments | Consulting | Oliver Wyman Group
Segment Reporting Information [Line Items]
Revenue	810	781	2,436	2,266
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (18)	$ (14)	$ (49)	$ (45)