Marsh & McLennan Companies (MMC) 10-Q 22 Jul 21 2021 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2021	Jul. 16, 2021
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2021
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		506,625,935
Entity Central Index Key	0000062709
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q2
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 (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Income Statement [Abstract]
Revenue	$ 5,017	$ 4,189	$ 10,100	$ 8,840
Expense:
Compensation and benefits	2,860	2,429	5,667	4,984
Other operating expenses	929	875	1,847	1,901
Operating expenses	3,789	3,304	7,514	6,885
Operating income	1,228	885	2,586	1,955
Other net benefit credits	71	63	142	127
Interest income	1	2	1	4
Interest expense	(110)	(132)	(228)	(259)
Investment income (loss)	19	(31)	30	(33)
Income before income taxes	1,209	787	2,531	1,794
Income tax expense	382	207	706	447
Net income before non-controlling interests	827	580	1,825	1,347
Less: Net income attributable to non-controlling interests	7	8	22	21
Net income attributable to the Company	$ 820	$ 572	$ 1,803	$ 1,326
Net income per share attributable to the Company:
Basic (usd per share)	$ 1.61	$ 1.13	$ 3.55	$ 2.62
Diluted (usd per share)	$ 1.60	$ 1.12	$ 3.51	$ 2.60
Average number of shares outstanding:
Basic (in shares)	508	506	508	505
Diluted (in shares)	513	511	514	510
Shares outstanding (in shares)	507	506	507	506

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Statement of Comprehensive Income [Abstract]
Net income before non-controlling interests	$ 827	$ 580	$ 1,825	$ 1,347
Other comprehensive income (loss), before tax:
Foreign currency translation adjustments	24	241	(67)	(700)
Gain related to pension/post-retirement plans	24	34	30	209
Other comprehensive income (loss), before tax	48	275	(37)	(491)
Income tax expense on other comprehensive income	4	10	6	36
Other comprehensive income (loss), net of tax	44	265	(43)	(527)
Comprehensive income	871	845	1,782	820
Less: comprehensive income attributable to non-controlling interest	7	8	22	21
Comprehensive income attributable to the Company	$ 864	$ 837	$ 1,760	$ 799

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 888	$ 2,089
Receivables
Commissions and fees	5,359	4,679
Advanced premiums and claims	113	112
Other	515	677
Gross receivables	5,987	5,468
Less-allowance for credit losses	(148)	(142)
Net receivables	5,839	5,326
Other current assets	846	740
Total current assets	7,573	8,155
Goodwill	15,775	15,517
Other intangible assets	2,717	2,699
Fixed assets (net of accumulated depreciation and amortization of $2,317 at June 30, 2021 and $2,159 at December 31, 2020)	816	856
Pension related assets	1,911	1,768
Right of use assets	1,983	1,894
Deferred tax assets	669	702
Other assets	1,509	1,458
Total assets	32,953	33,049
Current liabilities:
Short-term debt	516	517
Accounts payable and accrued liabilities	2,830	3,050
Accrued compensation and employee benefits	1,775	2,400
Current lease liabilities	342	342
Accrued income taxes	353	247
Total current liabilities	5,816	6,556
Fiduciary liabilities	9,936	8,585
Less – cash and investments held in a fiduciary capacity	(9,936)	(8,585)
Net fiduciary liabilities	0	0
Long-term debt	10,257	10,796
Pension, post-retirement and post-employment benefits	2,539	2,662
Long-term lease liabilities	1,992	1,924
Liabilities for errors and omissions	365	366
Other liabilities	1,720	1,485
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 June 30, 2021 and December 31, 2020	561	561
Additional paid-in capital	945	943
Retained earnings	17,597	16,272
Accumulated other comprehensive loss	(5,153)	(5,110)
Non-controlling interests	156	156
Stockholders' equity before treasury stock	14,106	12,822
Less – treasury shares, at cost, 53,676,347 shares at June 30, 2021 and 52,914,550 shares at December 31, 2020	(3,842)	(3,562)
Total equity	10,264	9,260
Total liabilities and stockholders' equity	$ 32,953	$ 33,049

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Fixed assets, accumulated depreciation and amortization	$ 2,317	$ 2,159
Preferred stock, par value (usd per share)	$ 1	$ 1
Preferred stock, shares authorized	6,000,000	6,000,000
Preferred stock, shares issued	0	0
Common stock, par value (usd per share)	$ 1	$ 1
Common stock, shares authorized	1,600,000,000	1,600,000,000
Common stock, shares issued	560,641,640	560,641,640
Treasury shares, shares	53,676,347	52,914,550

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Operating cash flows:
Net income before non-controlling interests	$ 1,825	$ 1,347
Adjustments to reconcile net income used for operations:
Depreciation and amortization of fixed assets and capitalized software	201	188
Amortization of intangible assets	189	174
Non cash lease expense	158	165
Adjustments and payments related to contingent consideration assets and liabilities	7	(30)
Provision for deferred income taxes	119	7
Net (gain) loss on investments	(30)	33
Net (gain) loss on disposition of assets	(43)	5
Share-based compensation expense	176	147
Changes in assets and liabilities:
Net receivables	(551)	(389)
Other current assets	(106)	(81)
Other assets	(180)	140
Accounts payable and accrued liabilities	(116)	(129)
Accrued compensation and employee benefits	(642)	(848)
Accrued income taxes	109	204
Contributions to pension and other benefit plans in excess of current year credit	(187)	(165)
Other liabilities	88	(20)
Operating lease liabilities	(172)	(164)
Effect of exchange rate changes	(95)	(6)
Net cash provided by operations	750	578
Financing cash flows:
Purchase of treasury shares	(434)	0
Borrowings from term-loan and credit facilities	0	1,000
Proceeds from issuance of debt	0	737
Repayments of debt	(509)	(507)
Purchase of non-controlling interests	0	(3)
Shares withheld for taxes on vested units – treasury shares	(98)	(115)
Issuance of common stock from treasury shares	75	66
Net payments of deferred and contingent consideration for acquisitions and dispositions	(26)	(69)
Distributions of non-controlling interests	(21)	(22)
Dividends paid	(478)	(466)
Net cash (used for) provided by financing activities	(1,491)	621
Investing cash flows:
Capital expenditures	(151)	(200)
Net (purchase) sale of long term investments	(2)	103
Dispositions	81	93
Acquisitions	(363)	(562)
Other, net	(2)	2
Net cash used for investing activities	(437)	(564)
Effect of exchange rate changes on cash and cash equivalents	(23)	(79)
(Decrease) increase in cash and cash equivalents	(1,201)	556
Cash and cash equivalents at beginning of period	2,089	1,155
Cash and cash equivalents at end of period	$ 888	$ 1,711

Consolidated Statements of Equi

Consolidated Statements of Equity (Unaudited) - USD ($) $ in Millions	Total	COMMON STOCK	ADDITIONAL PAID-IN CAPITAL	RETAINED EARNINGS	ACCUMULATED OTHER COMPREHENSIVE (LOSS) INCOME	TREASURY SHARES	NON-CONTROLLING INTERESTS
Balance, beginning of period at Dec. 31, 2019		$ 561	$ 862	$ 15,199	$ (5,055)	$ (3,774)	$ 150
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(63)
Issuance of shares under stock compensation plans and employee stock purchase plans			16			147
Other			(1)
Net income attributable to the Company	$ 1,347			1,326			21
Dividend equivalents declared				(6)
Dividends declared				(459)
Other comprehensive income (loss), net of tax	(527)				(527)
Purchase of treasury shares						0
Net non-controlling interests acquired (disposed)							(1)
Distributions and other changes							(4)
Balance, end of period at Jun. 30, 2020	$ 8,392	561	814	16,060	(5,582)	(3,627)	166
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0.910
Balance, beginning of period at Mar. 31, 2020		561	746	15,490	(5,847)	(3,655)	156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			66
Issuance of shares under stock compensation plans and employee stock purchase plans			2			28
Other			0
Net income attributable to the Company	$ 580			572			8
Dividend equivalents declared				(2)
Dividends declared				0
Other comprehensive income (loss), net of tax	265				265
Purchase of treasury shares						0
Net non-controlling interests acquired (disposed)							2
Distributions and other changes							0
Balance, end of period at Jun. 30, 2020	$ 8,392	561	814	16,060	(5,582)	(3,627)	166
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0
Balance, beginning of period at Dec. 31, 2020	$ 9,260	561	943	16,272	(5,110)	(3,562)	156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(48)
Issuance of shares under stock compensation plans and employee stock purchase plans			50			154
Other			0
Net income attributable to the Company	1,825			1,803			22
Dividend equivalents declared				(6)
Dividends declared				(472)
Other comprehensive income (loss), net of tax	(43)				(43)
Purchase of treasury shares	(445)					(434)
Net non-controlling interests acquired (disposed)							0
Distributions and other changes							(22)
Balance, end of period at Jun. 30, 2021	$ 10,264	561	945	17,597	(5,153)	(3,842)	156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0.930
Balance, beginning of period at Mar. 31, 2021		561	851	16,780	(5,197)	(3,561)	162
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			85
Issuance of shares under stock compensation plans and employee stock purchase plans			9			41
Other			0
Net income attributable to the Company	$ 827			820			7
Dividend equivalents declared				(3)
Dividends declared				0
Other comprehensive income (loss), net of tax	44				44
Purchase of treasury shares						(322)
Net non-controlling interests acquired (disposed)							0
Distributions and other changes							(13)
Balance, end of period at Jun. 30, 2021	$ 10,264	$ 561	$ 945	$ 17,597	$ (5,153)	$ (3,842)	$ 156
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0.465

Nature of Operations

Nature of Operations	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations Marsh & McLennan Companies, Inc. (the "Company" or "Marsh McLennan"), 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") provides risk management solutions, services, advice and insurance broking, reinsurance broking and insurance program management 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 advises individual and commercial clients of all sizes on insurance broking and innovative risk management solutions. Guy Carpenter develops advanced risk, reinsurance and capital strategies that help clients grow profitably and pursue emerging opportunities. The Company conducts business in its Consulting segment through Mercer and Oliver Wyman Group. Mercer provides consulting expertise, advice, services and solutions in the areas of health, wealth and career consulting services and products. Oliver Wyman Group provides specialized management and economic and brand consulting services. Business Update Related To COVID-19 It has been well over a year since the World Health Organization declared COVID-19 a pandemic in March 2020, and the pandemic continues to impact virtually every geography in which the Company operates. The safety and well-being of our colleagues remains our first priority, while we continue to serve the needs of our clients. In certain parts of the world, governments continue to ease restrictions or fully reopen their economies as initial distribution and uptake of vaccinations contribute to reduced infection rate of the virus. While the vaccines are effective, uneven distribution has left many countries vulnerable to continued outbreaks and the emergence of variants of the virus has led to increased infection rates, even in areas where the vaccination rate is relatively high. Although the vast majority of colleagues continue to work in a remote environment, the Company will provide guidelines on a gradual and phased return to the office depending on the level of virus containment and local health and safety regulations. The Company expects to continue to service clients effectively in the current remote environment and as colleagues gradually return to the office. Although the pandemic is ongoing, the Company had strong revenue growth through the first six months of 2021 and benefited from the continued recovery of the global economy. However, uncertainty remains in the economic outlook and the ultimate extent of COVID-19 impact to the Company will depend on future developments that it is unable to predict, including new “waves” of infection from emerging variants of the virus, potential renewed restrictions by various governments or agencies, and the effectiveness and distribution rate of vaccines .

Principles of Consolidation and

Principles of Consolidation and Other Matters	6 Months Ended
	Jun. 30, 2021
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 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, 2020 (the "2020 Form 10-K"). 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 six month periods ended June 30, 2021 and 2020. Estimates: 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: • the allowance for current expected credit losses on receivables, • 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, • useful lives assigned to long-lived assets, and depreciation and amortization, • 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 any COVID-19 potential impacts to its customer base in various industries and geographies and has concluded through June 30, 2021, that COVID-19 did not have a material adverse impact on the Company's financial position or estimates. During the second quarter of 2020, the Company recorded a revenue reduction of $36 million for estimated commission revenue accounted for on a point in time basis. The reduction relates to policy periods incepted from the third quarter of 2019 through the second quarter of 2020. 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 data and industry specific economic data reflecting the impact of the COVID-19 pandemic . The ultimate extent to which COVID-19 will directly or indirectly impact the Company’s businesses, results of operations and financial condition will depend on numerous evolving factors and future developments that it is not able to predict. 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 United States or as collateral under captive insurance arrangements. At June 30, 2021, the Company maintained $304 million compared to $270 million at December 31, 2020 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 immaterial to the consolidated statement of income for the three and six month periods ended June 30, 2021. Investments The caption "Investment income (loss)" 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 that 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 the Company's proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for using the equity method of accounting are included in "other assets" in the consolidated balance sheets. The Company recorded net investment income of $19 million and $30 million for the three and six months ended June 30, 2021 compared to net investment losses of $31 million and $33 million for the same periods last year. The income in 2021 is primarily driven by gains in the Company's private equity investments compared to losses for the same periods in prior year. The three and six month periods ending June 30, 2020 include a loss of $23 million from the sale of shares of Alexander Forbes and losses related to the Company's private equity fund investments. Income Taxes On June 10, 2021, the U.K. enacted tax legislation commonly referred to as the “Finance Act 2021”. The legislation provides for an increase in the corporate income tax rate applicable to U.K. based entities from 19% to 25%, effective April 1, 2023. The Company recorded a net charge of $100 million in the second quarter of 2021, which reflects the re-measurement of the Company's U.K. deferred tax assets and liabilities upon enactment of the legislation. The Company's effective tax rate in the second quarter of 2021 was 31.6% compared with 26.2% in the second quarter of 2020. The effective tax rates for the first six months of 2021 and 2020 were 27.9% and 24.9%, respectively. The rate in the second quarter of 2021 reflects the charge of re-measuring the Company’s U.K. deferred tax assets and liabilities upon the enactment of legislation increasing the U.K. corporate income tax rate from 19% to 25%, effective April 1, 2023. This was the most significant discrete item in the second quarter, increasing the Company’s effective tax rate by 8.3% and 4% for the three and six month periods ended June 30, 2020, respectively. The tax rates in both periods reflect 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 and nontaxable adjustments to contingent acquisition consideration. 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 limitation. Changes in tax laws or tax rulings may have a significant impact on our effective tax rate. 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 was $94 million at June 30, 2021 and $98 million at December 31, 2020. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $33 million within the next twelve months due to settlements of audits and expirations of statutes of limitation. Integration and Restructuring Charges 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 right-of-use 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 right-of-use 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 right-of-use asset is determined based on the present value of the estimated net cash flows related to the property. Contractual costs outside of the right-of-use 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 based 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 integration and 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.

Revenue

Revenue	6 Months Ended
	Jun. 30, 2021
Revenue from Contract with Customer [Abstract]
Revenue	RevenueThe 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. The entity applies the following steps to achieve that principle: 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. 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. The Company's revenue recognition guidance is provided in more detail in Note 2 of the consolidated financial statements and the notes thereto included in Form 10-K for the year ended December 31, 2020. The following schedule disaggregates components of the Company's revenue: Three Months Ended Six Months Ended (In millions) 2021 2020 2021 2020 Marsh: EMEA $ 796 $ 597 $ 1,633 $ 1,351 Asia Pacific 347 298 621 536 Latin America 103 99 193 190 Total International 1,246 994 2,447 2,077 U.S./Canada 1,404 1,167 2,528 2,145 Total Marsh 2,650 2,161 4,975 4,222 Guy Carpenter 488 433 1,383 1,260 Subtotal 3,138 2,594 6,358 5,482 Fiduciary interest income 3 9 8 32 Total Risk and Insurance Services $ 3,141 $ 2,603 $ 6,366 $ 5,514 Mercer: Wealth $ 625 $ 561 $ 1,248 $ 1,153 Health 462 432 949 918 Career 187 156 365 329 Total Mercer 1,274 1,149 2,562 2,400 Oliver Wyman Group 618 467 1,203 978 Total Consulting $ 1,892 $ 1,616 $ 3,765 $ 3,378 The Company recognizes commission revenue from arrangements for a significant portion of its brokerage arrangements at a point in time on the effective date of the underlying policy. Commission revenue is estimated using historical information about the risks to be covered over the policy period, some of which are dependent on variable factors such as number of employees covered, covered payroll, airline passenger miles flown, shipped tonnage of marine cargo and others. The following schedule provides contract assets and contract liabilities information from contracts with customers: (In millions) June 30, 2021 December 31, 2020 Contract assets $ 323 $ 236 Contract liabilities $ 759 $ 676 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. 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 in the first six months of 2021 and 2020 that was included in the contract liability balance at the beginning of each of those years was $380 million and $418 million, respectively. The amount of revenue recognized in the first six months of 2021 and 2020 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 $72 million and $67 million, respectively.

Fiduciary Assets and Liabilitie

Fiduciary Assets and Liabilities	6 Months Ended
	Jun. 30, 2021
Fiduciary Assets And Liabilities [Abstract]
Fiduciary Assets and Liabilities	Fiduciary Assets and Liabilities In its capacity as an insurance broker or agent, the Company 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. Un-remitted insurance premiums and claims proceeds are held by the Company in a fiduciary capacity. Risk and Insurance Services revenue includes interest on fiduciary funds ("fiduciary interest income") of $3 million and $8 million for the three month and six month periods ended June 30, 2021, respectively, and $9 million and $32 million for the three and six month periods ended June 30, 2020, respectively. The decrease in 2021 compared to 2020 reflects the impact of lower interest rates partially offset by a higher level of average invested funds. Since fiduciary assets are not available for corporate use, they are shown in the consolidated balance sheets as an offset to fiduciary liabilities. Net uncollected premiums and claims and the related payables amounted to $14.2 billion at June 30, 2021 and $11.2 billion at December 31, 2020. The Company is not a principal to the contracts under which the right to receive premiums or the right to receive reimbursement of insured losses arises. Accordingly, net uncollected premiums and claims and the related payables are not assets and liabilities of the Company and are not included in the accompanying consolidated balance sheets. In certain instances, the Company advances premiums, refunds or claims to insurance underwriters or insureds prior to collection. These advances are made from corporate funds and are reflected in the accompanying consolidated balance sheets as receivables.

Per Share Data

Per Share Data	6 Months Ended
	Jun. 30, 2021
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 Six Months Ended (In millions, except per share amounts) 2021 2020 2021 2020 Net income before non-controlling interests $ 827 $ 580 $ 1,825 $ 1,347 Less: Net income attributable to non-controlling interests 7 8 22 21 Net income attributable to the Company $ 820 $ 572 $ 1,803 $ 1,326 Basic weighted average common shares outstanding 508 506 508 505 Dilutive effect of potentially issuable common shares 5 5 6 5 Diluted weighted average common shares outstanding 513 511 514 510 Average stock price used to calculate common stock equivalents $ 134.04 $ 101.17 $ 124.50 $ 104.14

Supplemental Disclosures to the

Supplemental Disclosures to the Consolidated Statements of Cash Flows	6 Months Ended
	Jun. 30, 2021
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 schedule provides additional information concerning acquisitions, interest and income taxes paid for the six-month periods ended June 30, 2021 and 2020. (In millions) 2021 2020 Assets acquired, excluding cash $ 561 $ 752 Liabilities assumed (60) (29) Contingent/deferred purchase consideration (138) (161) Net cash outflow for current year acquisitions $ 363 $ 562 (In millions) 2021 2020 Interest paid $ 234 $ 248 Income taxes paid, net of refunds $ 403 $ 227 The classification of contingent consideration in the statement of cash flows is dependent upon whether the 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 a financing activity. The Company paid deferred and contingent consideration of $97 million for the six months ended June 30, 2021. This consisted of deferred purchase consideration related to prior years' acquisitions of $84 million and contingent purchase consideration of $13 million. Cash flows from financing activities also reflect the receipt of contingent consideration of $71 million related to prior year dispositions. For the six months ended June 30, 2020, the Company paid deferred and contingent consideration of $69 million, consisting of deferred purchase consideration related to prior years' acquisitions of $27 million and contingent consideration of $42 million. The following amounts are included in the operating section of the consolidated statements of cash flows. For the six months ended June 30, 2021, the Company recorded an expense for adjustments to contingent consideration liabilities of $17 million and made contingent consideration payments of $4 million. In addition, the Company recorded income of $24 million, primarily related to the settlement of contingent consideration receivables and received cash of $18 million related to prior year dispositions. For the six months ended June 30, 2020, the Company recorded an expense for adjustments to contingent consideration liabilities of $6 million and made contingent consideration payments of $36 million. The Company had non-cash issuances of common stock under its share-based payment plan of $228 million and $213 million for the six months ended June 30, 2021 and 2020, respectively. The Company recorded stock-based compensation expense for equity awards related to restricted stock units, performance stock units and stock options of $176 million and $147 million for the six-months ended June 30, 2021 and 2020, respectively.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The changes, net of tax, in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the three and six month periods ended June 30, 2021 and 2020, including amounts reclassified out of AOCI, are as follows: (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of April 1, 2021 $ (4,122) $ (1,075) $ (5,197) Other comprehensive (loss) income before reclassifications (16) 24 8 Amounts reclassified from accumulated other comprehensive income 36 — 36 Net current period other comprehensive income 20 24 44 Balance as of June 30, 2021 $ (4,102) $ (1,051) $ (5,153) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of April 1, 2020 $ (3,374) $ (2,473) $ (5,847) Other comprehensive (loss) income before reclassifications (3) 237 234 Amounts reclassified from accumulated other comprehensive income 31 — 31 Net current period other comprehensive income 28 237 265 Balance as of June 30, 2020 $ (3,346) $ (2,236) $ (5,582) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2020 $ (4,126) $ (984) $ (5,110) Other comprehensive loss before reclassifications (52) (67) (119) Amounts reclassified from accumulated other comprehensive income 76 — 76 Net current period other comprehensive income (loss) 24 (67) (43) Balance as of June 30, 2021 $ (4,102) $ (1,051) $ (5,153) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2019 $ (3,512) $ (1,543) $ (5,055) Other comprehensive income (loss) before reclassifications 106 (693) (587) Amounts reclassified from accumulated other comprehensive income 60 — 60 Net current period other comprehensive income (loss) 166 (693) (527) Balance as of June 30, 2020 $ (3,346) $ (2,236) $ (5,582) The components of other comprehensive income (loss) for the three and six-month periods ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, 2021 2020 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 24 $ — $ 24 $ 241 $ 4 $ 237 Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (1) — (1) (1) — (1) Net actuarial losses (a) 52 15 37 40 8 32 Subtotal 51 15 36 39 8 31 Foreign currency translation adjustments (44) (12) (32) (5) (2) (3) Effect of remeasurement 15 1 14 — — — Effect of settlement 2 — 2 — — — Pension/post-retirement plans gains 24 4 20 34 6 28 Other comprehensive income $ 48 $ 4 $ 44 $ 275 $ 10 $ 265 (a) Components of net periodic pension cost are 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. Six Months Ended June 30, 2021 2020 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (67) $ — $ (67) $ (700) $ (7) $ (693) Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (1) — (1) (1) — (1) Net actuarial losses (a) 104 27 77 80 19 61 Subtotal 103 27 76 79 19 60 Foreign currency translation adjustments (81) (20) (61) 130 24 106 Other adjustments (7) (2) (5) — — — Effect of remeasurement 13 1 12 — — — Effect of settlement 2 — 2 — — — Pension/post-retirement plans gains 30 6 24 209 43 166 Other comprehensive (loss) income $ (37) $ 6 $ (43) $ (491) $ 36 $ (527) (a) Components of net periodic pension cost are 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	6 Months Ended
	Jun. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Acquisitions and Dispositions	Acquisitions and DispositionsThe 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 two acquisitions during the first six months ended June 30, 2021: • April – Marsh McLennan Agency ("MMA") acquired PayneWest Insurance, Inc., a Montana-based full-service broker providing business insurance, surety, employee benefits and personal insurance services to companies and individuals, and The Pryor Group, LLC, a Texas-based full-service broker providing business insurance with a specialty in quick service restaurants and the personal lines of franchise owners. Total purchase consideration for acquisitions made during the six months ended June 30, 2021 was $505 million, which consisted of cash paid of $367 million and deferred purchase consideration and estimated contingent consideration of $138 million. Contingent consideration arrangements are based primarily on earnings before interest, tax, depreciation and amortization ("EBITDA") or revenue targets over a period of two The following table presents the preliminary allocation of purchase consideration to the assets acquired and liabilities assumed during 2021 based on the estimated fair values for the acquisitions as of their respective acquisition dates: Acquisitions through June 30, 2021 (In millions) Cash $ 367 Estimated fair value of deferred/contingent consideration 138 Total consideration $ 505 Allocation of purchase price: Cash and cash equivalents $ 4 Accounts receivable, net 30 Other current assets 1 Fixed assets, net 4 Other intangible assets 188 Goodwill 338 Total assets acquired 565 Current liabilities 23 Other liabilities 37 Total liabilities assumed 60 Net assets acquired $ 505 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. 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 chart provides information about intangible assets acquired during 2021: Intangible assets through June 30, 2021 (In millions) Amount Weighted Average Amortization Period Client relationships $ 169 14.0 years Other 19 3.9 years $ 188 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 six month period ended June 30, 2021 include revenue of approximately $35 million and operating income of $2 million for acquisitions made in 2021. The consolidated statements of income for the three and six month periods ended June 30, 2020 included approximately $48 million and $63 million of revenue, respectively, and operating income of $7 million and $11 million, respectively, related to acquisitions made in 2020. Dispositions During the first six months of 2021, the Company sold certain businesses in the U.S. and the U.K. for cash proceeds of approximately $81 million and recognized a net gain of approximately $50 million, primarily related to the commercial networks business in the U.K that provided broking and back-office solutions for small independent brokers. Prior-Year Acquisitions The Risk and Insurance Services segment completed seven acquisitions during 2020: • January – MMA acquired Momentous Insurance Brokerage Inc., a California-based full-service risk management and employee benefits firm specializing in high net worth private client services and insurance solutions for the entertainment industry, and Ironwood Insurance Services, LLC, an Atlanta-based broker that provides commercial property/casualty insurance, employee benefits, and private client solutions to mid-size businesses and individuals across the U.S. • April – MMA acquired Assurance Holdings, Inc., an Illinois-based full service brokerage providing business insurance, employee benefits, private client insurance, and retirement services to businesses and individuals across the U.S. • June – MMA acquired Nico Insurance Services, Inc., a California-based agency providing employee benefits solutions to groups and individuals. • December – MMA acquired Heritage Insurance Services, Inc., a Kentucky-based full service broker that provides commercial property and casualty and personal lines primarily in the trucking and transportation industry, Inspro Insurance, Inc., a Nebraska-based full service broker that provides commercial property and casualty insurance, personal lines and employee benefits services, and Compass Financial Partners, LLC, a North Carolina-based retirement consulting and investment advisory firm. Total purchase consideration for acquisitions made during the six months ended June 30, 2020 was approximately $737 million, which consisted of cash paid of $576 million and deferred purchase and estimated contingent consideration of $161 million. Contingent consideration arrangements are based primarily on earnings before interest, tax, depreciation and amortization ("EBITDA") or revenue targets over a period of two Prior year dispositions In the first six months of 2020, the Company sold certain businesses primarily in the U.S., U.K. and Canada for cash proceeds of approximately $93 million. Pro-Forma Information The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during 2021 and 2020. In accordance with accounting guidance related to pro-forma disclosures, the information presented for acquisitions made in 2021 is as if they occurred on January 1, 2020 and reflects acquisitions made in 2020 is as if they occurred on January 1, 2019. The unaudited pro-forma information adjusts for the effects of amortization of acquired intangibles. 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 Six Months Ended (In millions, except per share figures) 2021 2020 2021 2020 Revenue $ 5,017 $ 4,231 $ 10,137 $ 8,970 Net income attributable to the Company $ 820 $ 577 $ 1,806 $ 1,332 Basic net income per share attributable to the Company $ 1.61 $ 1.14 $ 3.55 $ 2.64 Diluted net income per share attributable to the Company $ 1.60 $ 1.13 $ 3.52 $ 2.61

Goodwill and Other Intangibles

Goodwill and Other Intangibles	6 Months Ended
	Jun. 30, 2021
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 impairment may have occurred. The Company performs the annual impairment assessment for each of its reporting units during the third quarter of each year. 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, the Company may elect to proceed directly to the quantitative goodwill impairment test. In 2020, the Company elected to perform a qualitative impairment assessment. 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 2019; • 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. The Company completed its qualitative assessment in the third quarter of 2020 and concluded that goodwill was not impaired. 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 does not have any indefinite lived intangible assets. Changes in the carrying amount of goodwill are as follows: June 30, (In millions) 2021 2020 Balance as of January 1, $ 15,517 $ 14,671 Goodwill acquired 338 466 Other adjustments (a) (80) (340) Balance at June 30, $ 15,775 $ 14,797 (a) Primarily reflects the impact of foreign exchange. The goodwill arising from the acquisitions in 2021 and 2020 consist 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 2021 and 2020 included approximately $338 million and $466 million, respectively, of which approximately $1 million and $141 million is deductible for tax purposes, and is primarily related to the Risk and Insurance Services segment. Goodwill allocable to the Company’s reportable segments at June 30, 2021 is as follows: Risk and Insurance Services, $11.9 billion and Consulting, $3.9 billion. The gross cost and accumulated amortization of identified intangible assets at June 30, 2021 and December 31, 2020 are as follows: June 30, 2021 December 31, 2020 (In millions) Gross Accumulated Net Gross Accumulated Net Client relationships $ 3,882 $ 1,320 $ 2,562 $ 3,713 $ 1,170 $ 2,543 Other (a) 407 252 155 386 230 156 Amortized intangibles $ 4,289 $ 1,572 $ 2,717 $ 4,099 $ 1,400 $ 2,699 (a) Primarily non-compete agreements, trade names and developed technology. Aggregate amortization expense for the six months ended June 30, 2021 and 2020 was $189 million and $174 million, respectively. The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2021 (excludes amortization through June 30, 2021) $ 182 2022 337 2023 309 2024 289 2025 251 Subsequent years 1,349 $ 2,717

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2021
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 as defined by the FASB. 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). Assets and liabilities using Level 2 inputs are related to an equity security. 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 Mutual 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 mutual funds are valued using a valuation technique that results in price per share at $1.00. 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 two The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis as of June 30, 2021 and December 31, 2020: Identical Assets Observable Inputs Unobservable Total (In millions) 06/30/21 12/31/20 06/30/21 12/31/20 06/30/21 12/31/20 06/30/21 12/31/20 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 63 $ 59 $ — $ — $ — $ — $ 63 $ 59 Mutual funds (a) 186 186 — — — — 186 186 Money market funds (b) 75 587 — — — — 75 587 Other equity investment (a) — — 8 8 — — 8 8 Contingent purchase consideration assets (c) — — — — 6 68 6 68 Total assets measured at fair value $ 324 $ 832 $ 8 $ 8 $ 6 $ 68 $ 338 $ 908 Fiduciary Assets: U.S. treasury bills $ — $ 150 $ — $ — $ — $ — $ — $ 150 Money market funds 243 173 — — — — 243 173 Total fiduciary assets measured $ 243 $ 323 $ — $ — $ — $ — $ 243 $ 323 Liabilities: Contingent purchase consideration liability (d) $ — $ — $ — $ — $ 340 $ 243 $ 340 $ 243 Total liabilities measured at fair value $ — $ — $ — $ — $ 340 $ 243 $ 340 $ 243 (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 chart reflect contingent purchase consideration from the sale of businesses during 2019. The change in the contingent purchase consideration assets from December 31, 2020 is driven primarily by cash receipts of approximately $89 million. This decrease was partially offset by the impact of accretion and adjustments to the fair value of the contingent purchase consideration assets. During the six months ended June 30, 2021, there were no assets or liabilities that were transferred between any of the levels. The following table sets forth a summary of the changes in fair value of the Company’s Level 3 liabilities for the three and six month periods ended June 30, 2021 and 2020: Three Months Ended Six Months Ended (In millions) 2021 2020 2021 2020 Balance at beginning of period $ 233 $ 239 $ 243 $ 225 Net additions 97 66 97 96 Payments (6) (65) (17) (78) Revaluation impact 16 (11) 17 (10) Other (a) — 4 — — Balance at June 30, $ 340 $ 233 $ 340 $ 233 (a) Primarily reflects the impact of foreign exchange. Long-Term Investments The Company holds 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 $315 million and $280 million at June 30, 2021 and December 31, 2020, respectively. Investments in Public and Private Companies The Company has investments in private insurance and consulting companies with a carrying value of $175 million and $169 million at June 30, 2021 and December 31, 2020, 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 $140 million and $111 million at June 30, 2021 and December 31, 2020, 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 (loss) line in the consolidated statements of income. These investments are included in other assets in the consolidated balance sheets. The Company recorded net investment gains of $17 million and $27 million for the three and six month periods ended June 30, 2021, respectively, and losses of $6 million and $7 million from these investments for the same periods in 2020. Other Investments At June 30, 2021 and December 31, 2020, the Company held certain equity investments with readily determinable market values of $76 million and $72 million, respectively, including an investment in the common stock of Alexander Forbes ("AF") of $58 million at June 30, 2021 and $54 million at December 31, 2020. The Company also held investments without readily determinable market values of $34 million at June 30, 2021 and $33 million at December 31, 2020.

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2021
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

Leases

Leases	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Leases	Leases A lease is defined as a party obtaining the right to use an asset legally owned by another party. The Company determines if an arrangement is a lease at inception. Operating leases are recognized on the balance sheet as Right-of-Use ("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. The Company uses discount rates to determine the present value of future lease payments. The Company primarily uses its incremental borrowing rate adjusted to reflect a secured rate, based on the information available for leases, including the lease term and interest rate environment in the country in which the lease exists. The lease terms used to calculate the ROU asset and lease liability may include options to extend or terminate when it is reasonably certain that the Company will exercise that option. 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. Leases are negotiated with third-parties and, in some instances contain renewal, expansion and termination options. The Company also subleases certain office facilities to third-parties when the Company no longer utilizes the space. None of the Company’s leases restrict the payment of dividends or the incurrence of debt or additional lease obligations, or contain significant purchase options. In addition to the base rental costs, our lease agreements generally provide for rent escalations resulting from increased assessments for real estate taxes and other charges. A portion of our real estate lease portfolio contains base rents subject to annual changes in the Consumer Price Index ("CPI") as well as charges for operating expenses which are reimbursable to the landlord based on actual usage. Changes to the CPI and payments for such reimbursable operating expenses are considered variable and are recognized as variable lease costs in the period in which the obligation for those payments is incurred. Approximately 99% of the Company’s lease obligations are for the use of office space. All of the Company’s material leases are operating leases. As a practical expedient, the Company elected an accounting policy not to separate non-lease components from lease components and instead account as a single lease component. The Company also elected not to recognize ROU assets and lease liabilities for leases that, at the commencement date, are for 12 months or less. The following chart provides additional information about the Company’s property leases: Three Months Ended June 30, Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Lease Cost: Operating lease cost $ 95 $ 97 $ 189 $ 189 Short-term lease cost 2 1 3 2 Variable lease cost 26 27 63 64 Sublease income (5) (5) (13) (10) Net lease cost $ 118 $ 120 $ 242 $ 245 Other information: Operating cash outflows from operating leases $ 204 $ 197 Right of use assets obtained in exchange for new operating lease liabilities $ 251 $ 129 Weighted-average remaining lease term – real estate 9.1 years 8.5 years Weighted-average discount rate – real estate leases 2.76 % 3.05 % Future minimum lease payments for the Company’s operating leases as of June 30, 2021 are as follows: Payment Dates (In millions) Real Estate Leases Remainder of 2021 $ 208 2022 388 2023 340 2024 297 2025 265 2026 244 Subsequent years 901 Total future lease payments 2,643 Less: Imputed interest (309) Total $ 2,334 Current lease liabilities $ 342 Long-term lease liabilities 1,992 Total lease liabilities $ 2,334 Note: Table excludes obligations for leases with original terms of 12 months or less which have not been recognized as a right of use asset or liability in the consolidated balance sheets.

Retirement Benefits

Retirement Benefits	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Retirement Benefits	Retirement Benefits The Company maintains qualified and non-qualified defined benefit pension plans for some of its U.S. and non-U.S. eligible employees. The Company’s policy for funding its tax-qualified defined benefit pension plans is to contribute amounts at least sufficient to meet the funding requirements set forth in accordance with applicable law. The target asset allocation for the Company's U.S. plans is 64% equities and equity alternatives and 36% fixed income. At June 30, 2021 the actual allocation for the Company's U.S. Plan was 65% equities and equity alternatives and 35% fixed income. The target allocation for the U.K. Plans at June 30, 2021 is 27% equities and equity alternatives and 73% fixed income. At June 30, 2021, the actual allocation for the U.K. Plans was 29% equities and equity alternatives and 71% fixed income. The Company's U.K. Plans comprised approximately 81% of non-U.S. plan assets at December 31, 2020. 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 generally uses threshold-based portfolio re-balancing to ensure the actual portfolio remains consistent with target asset allocation ranges. The components of the net periodic benefit cost for defined benefit and other post-retirement plans are as follows: Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 10 $ 9 $ — $ — Interest cost 86 104 1 — Expected return on plan assets (211) (207) — — Recognized actuarial loss 51 40 — — Net periodic benefit (credit) cost $ (64) $ (54) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (62) $ (54) $ 1 $ — Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 20 $ 17 $ — $ — Interest cost 171 210 1 1 Expected return on plan assets (419) (417) — — Amortization of prior service credit — — (1) (1) Recognized actuarial loss 103 80 1 — Net periodic benefit (credit) cost $ (125) $ (110) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (123) $ (110) $ 1 $ — Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Compensation and benefits expense $ 10 $ 9 $ — $ — Other net benefit (credit) cost (72) (63) 1 — Total (credit) cost $ (62) $ (54) $ 1 $ — Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Compensation and benefits expense $ 20 $ 17 $ — $ — Other net benefit (credit) cost (143) (127) 1 — Total (credit) cost $ (123) $ (110) $ 1 $ — U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Interest cost $ 46 $ 54 $ — $ — Expected return on plan assets (81) (87) — — Recognized actuarial loss 22 18 — — Net periodic benefit credit $ (13) $ (15) $ — $ — U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Interest cost $ 92 $ 107 $ — $ — Expected return on plan assets (163) (173) — — Recognized actuarial loss 45 36 — — Net periodic benefit credit $ (26) $ (30) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 10 $ 9 $ — $ — Interest cost 40 50 1 — Expected return on plan assets (130) (120) — — Recognized actuarial loss 29 22 — — Net periodic benefit (credit) cost $ (51) $ (39) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (49) $ (39) $ 1 $ — Significant non-U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 20 $ 17 $ — $ — Interest cost 79 103 1 1 Expected return on plan assets (256) (244) — — Amortization of prior service credit — — (1) (1) Recognized actuarial loss 58 44 1 — Net periodic benefit (credit) cost $ (99) $ (80) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (97) $ (80) $ 1 $ — 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 Post-retirement June 30, 2021 2020 2021 2020 Weighted average assumptions: Expected return on plan assets 4.72 % 5.31 % — — Discount rate 1.92 % 2.57 % 2.42 % 2.72 % Rate of compensation increase 1.85 % 1.76 % — — The Company made approximately $57 million of contributions to its U.S. and non-U.S. defined benefit pension plans for the six months ended June 30, 2021. The Company expects to contribute approximat ely $72 million to its U.S. and non-U.S. defined benefit pension plans during the remainder of 2021. Defined Contribution Plans The Company maintains certain 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 was $78 million and $73 million for the six months ended June 30, 2021 and 2020, respectively. The cost of the U.K. DC Plans was $73 million and $64 million for the six months ended June 30, 2021 and 2020, respectively.

Debt

Debt	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Debt	Debt The Company’s outstanding debt is as follows: (In millions) June 30, December 31, Short-term: Current portion of long-term debt $ 516 $ 517 516 517 Long-term: Senior notes – 4.80% due 2021 — 500 Senior notes – 2.75% due 2022 499 499 Senior notes – 3.30% due 2023 349 349 Senior notes – 4.05% due 2023 249 249 Senior notes – 3.50% due 2024 598 598 Senior notes – 3.875% due 2024 996 995 Senior notes – 3.50% due 2025 498 498 Senior notes – 1.349% due 2026 660 677 Senior notes – 3.75% due 2026 598 597 Senior notes – 4.375% due 2029 1,499 1,499 Senior notes – 1.979% due 2030 645 664 Senior notes – 2.250% due 2030 738 737 Senior notes – 5.875% due 2033 298 298 Senior notes – 4.75% due 2039 495 495 Senior notes – 4.35% due 2047 493 493 Senior notes – 4.20% due 2048 592 592 Senior notes – 4.90% due 2049 1,237 1,237 Mortgage – 5.70% due 2035 324 331 Other 5 5 10,773 11,313 Less current portion 516 517 $ 10,257 $ 10,796 The senior notes in the table are registered by the Company with the Securities and Exchange Commission and are not guaranteed. On April 9, 2021, the Company increased its short-term commercial paper financing program to $2.0 billion from $1.5 billion. The Company had no commercial paper outstanding at June 30, 2021. Credit Facilities On April 2, 2021, the Company entered into an amended and restated multi-currency unsecured $2.8 billion five-year revolving credit facility ("New Facility"). The interest rate on the New Facility is based on LIBOR plus a fixed margin which varies with the Company’s credit ratings. The New Facility expires in April 2026 and requires the Company to maintain certain coverage and leverage ratios which are tested quarterly. The New Facility includes provisions for determining a LIBOR successor rate in the event LIBOR reference rates are no longer available or in certain other circumstances which are determined to make using an alternative rate desirable. As of June 30, 2021, the Company had no borrowings under this facility. In connection with the New Facility, the Company terminated its previous multicurrency unsecured $1.8 billion five-year revolving credit facility and its unsecured $1 billion 364-day unsecured revolving credit facility (“364-day Facility"). In January 2020, the Company closed on a $500 million one-year and $500 million two-year term loan facilities. In the first quarter of 2020 the Company borrowed $1 billion against these facilities, which were subsequently repaid during the third and fourth quarters of 2020. These two facilities were terminated as of December 31, 2020 after repayment of the initial draw down. Additional credit facilities, guarantees and letters of credit are maintained with various banks, primarily related to operations located outside the United States, aggregating $511 million at June 30, 2021 and $573 million at December 31, 2020. There were no outstanding borrowings under these facilities at June 30, 2021 and December 31, 2020. Senior Notes On April 15, 2021, the Company repaid $500 million of senior notes maturing in July 2021. In May 2020, the Company issued $750 million of Senior Notes due 2030. In March 2020, the Company repaid $500 million of maturing senior notes. Fair Value of Short-term and Long-term Debt The following table reflects the carrying values and estimated fair value of the Company’s short-term and long-term debt. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts 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. June 30, 2021 December 31, 2020 (In millions) Carrying Fair Carrying Fair Short-term debt $ 516 $ 523 $ 517 $ 523 Long-term debt $ 10,257 $ 11,853 $ 10,796 $ 12,858 The fair value of the Company's short-term debt consists primarily of term debt maturing within the next year and its fair value approximates its carrying value. The estimated fair value 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	6 Months Ended
	Jun. 30, 2021
Restructuring and Related Activities [Abstract]
Restructuring Costs	Restructuring Costs Jardine Lloyd Thompson Group plc ("JLT") Related Integration and Restructuring The Company is in the final stages of its integration of JLT, which the Company acquired in April 2019. The costs incurred in connection with the integration and restructuring of the combined businesses, primarily related to severance, real estate rationalization and technology, consulting fees related to the management of the integration processes and legal fees related to the rationalization of legal entity structures. Since the acquisition of JLT, the Company has incurred JLT integration and restructuring costs of $628 million through June 30, 2021. This reflects $19 million and $42 million of costs incurred for the three and six months ended June 30, 2021, respectively, compared to $57 million and $137 million, respectively, for the same period in the prior year. Costs recognized are based on applicable accounting guidance which includes accounting for disposal or exit activities, guidance related to impairment of long lived assets (for right of use 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. In connection with the JLT integration and restructuring, the Company incurred costs of $19 million and $42 million: $11 million and $27 million in RIS, $6 million and $12 million in Consulting, and $2 million and $3 million in Corporate for the three and six month periods ended June 30, 2021. The severance and related costs were included in compensation and benefits and the other costs were included in other operating expenses in the consolidated statement of income. Details of the JLT integration and restructuring activity from January 1, 2020 through June 30, 2021, are as follows: (In millions) Severance Real Estate Related Costs (a) Information Technology (a) Consulting and Other Outside Services (b) Total Liability at 1/1/20 $ 42 $ 5 $ — $ — $ 47 2020 charges 43 69 62 77 251 Cash payments (69) (25) (55) (77) (226) Non-cash charges — (42) (5) — (47) Liability at 12/31/20 $ 16 $ 7 $ 2 $ — $ 25 2021 charges 4 12 11 15 42 Cash payments (9) (7) (13) (15) (44) Non-cash charges — (8) — — (8) Liability at 6/30/21 $ 11 $ 4 $ — $ — $ 15 (a) Includes ROU asset impairments, data center contract termination costs and temporary infrastructure leasing costs. (b) Includes consulting fees related to the management of the integration processes and legal fees related to the rationalization of legal entity structures. Other Restructuring The Company incurred costs of $12 million and $23 million for the three and six month periods ended June 30, 2021 which reflect costs associated with the Company's global information technology and HR functions, and adjustments to restructuring liabilities for future rent under non-cancellable leases. The following details other restructuring liabilities for actions initiated prior to 2021: (In millions) Liability at Amounts Cash Non-Cash/Other Liability at 12/31/20 Amounts Cash Non-Cash/Other Liability at 6/30/21 Severance $ 51 $ 39 $ (54) $ — $ 36 $ 9 $ (28) $ — $ 17 Future rent under non-cancelable leases and other costs 51 50 (46) (10) 45 14 (19) (2) 38 Total $ 102 $ 89 $ (100) $ (10) $ 81 $ 23 $ (47) $ (2) $ 55

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Common Stock	Common Stock In November 2019, the Board of Directors of the Company authorized the Company to repurchase up to $2.5 billion in shares of the Company's common stock, which superseded any prior authorizations. During the first six months of 2021, the Company repurchased 3.4 million shares of its common stock for $445 million of which approximately $434 million was paid through June 30, 2021. As of June 30, 2021, the Company remained authorized to repurchase up to approximately $2 billion in shares of its common stock. There is no time limit on the authorization. During the first six months of 2020 there were no repurchases of the Company's common stock. The Company issued approximately 2.6 million and 2.8 million shares related to stock compensation and employee stock purchase plans during the first six months of 2021 and 2020, respectively.

Claims, Lawsuits And Other Cont

Claims, Lawsuits And Other Contingencies	6 Months Ended
	Jun. 30, 2021
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 in accordance with FASB guidance on Contingencies - Loss Contingencies, the Company uses case level reviews by inside and outside counsel, and internal actuarial analysis by Oliver Wyman, 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 United States and its various states, the European Union 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, receives requests for information in connection with governmental 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. • In 2017, JLT identified payments to a third-party introducer that had been directed to unapproved bank accounts. These payments related to reinsurance placements made on behalf of an Ecuadorian state-owned insurer between 2014 and 2017. In early 2018, JLT voluntarily reported this matter to law enforcement authorities. In February and March 2020, money laundering charges were filed in the United States against a former employee of JLT, the principals of the third-party introducer and a former official of the state-owned insurer. These individuals, including the former JLT employee, have since pleaded guilty to criminal charges. We are cooperating with all ongoing investigations related to this matter. • From 2014, Marsh Ltd. was engaged by Greensill Capital (UK) Limited 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 in the U.K., Australia, Germany and the U.S. Consulting Segment • In 2014, the FCA conducted an industry-wide review of the suitability of financial advice provided to individuals by a number of companies, including JLT, relating to enhanced transfer value ("ETV") defined benefit pension transfers. In January 2015, the FCA notified JLT that it was commissioning a Skilled Person review of ETV pension transfer advice given by JLT and a business acquired by JLT in 2012. Following the Skilled Person review which took place between 2015 and 2018, JLT engaged a compliance consulting firm to conduct an analysis of approximately 14,000 individual files to assess the suitability of the advice provided and, where appropriate, the amount of redress to be paid. In February 2019, prior to the completion of its acquisition by the Company, JLT recorded a gross liability of £59 million (or $77 million). This preliminary estimate by JLT, which reflected the projected redress amounts contained in the Skilled Person report, was based on a review of a limited number of files. Thereafter, the FCA expanded the scope of the thematic review. As of December 31, 2020, the updated redress liability, including the projected costs of completing the review, increased to £155 million (or $210 million) resulting from the expansion in the scop e of the review, and the significant progress made in completing the individual suitability reviews. Payments of redress and expenses during the first half of 2021 reduced the recorded liability to £99 million (or $137 million) as of June 30, 2021. We expect to finalize the suitability review and redress calculations for the limited number of files that remain outstanding and make the majority of redress payments by the end of the third quarter of 2021. We anticipate this gross liability will be partially offset by a contractual indemnity and insurance recoveries from third-party E&O insurers. At this time, we are unable to predict the likely timing, outcome or ultimate impact of the foregoing matters. 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. 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 describ ed 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 FASB guidance on Contingencies - Loss Contingencies. Except as described above, 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	6 Months Ended
	Jun. 30, 2021
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 to the Company’s 2020 Form 10-K. Segment performance is evaluated based on segment operating income, which includes directly related expenses, and charges or credits related to integration and 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 operating segments for the three and six month periods ended June 30, 2021 and 2020 are as follows: Three Months Ended Six Months Ended (In millions) Revenue Operating Income Revenue Operating Income 2021– Risk and Insurance Services $ 3,141 (a) $ 950 $ 6,366 (c) $ 2,010 Consulting 1,892 (b) 344 3,765 (d) 705 Total Operating Segments 5,033 1,294 10,131 2,715 Corporate/Eliminations (16) (66) (31) (129) Total Consolidated $ 5,017 $ 1,228 $ 10,100 $ 2,586 2020– Risk and Insurance Services $ 2,603 (a) $ 696 $ 5,514 (c) $ 1,550 Consulting 1,616 (b) 255 3,378 (d) 537 Total Operating Segments 4,219 951 8,892 2,087 Corporate/Eliminations (30) (66) (52) (132) Total Consolidated $ 4,189 $ 885 $ 8,840 $ 1,955 (a) Includes inter-segment revenue of $4 million in both 2021 and 2020, interest income on fiduciary funds of $3 million and $9 million in 2021 and 2020, respectively, and equity method income of $14 million in both 2021 and 2020. (b) Includes inter-segment revenue of $12 million and $26 million in 2021 and 2020, respectively. (c) Includes inter-segment revenue of $4 million and $5 million in 2021 and 2020, respectively, interest income on fiduciary funds of $8 million and $32 million in 2021 and 2020, respectively, and equity method income of $17 million and $13 million in 2021 and 2020, respectively. (d) Includes inter-segment revenue of $27 million and $47 million in 2021 and 2020, respectively, and equity method income of $4 million in 2020 and none in 2021. Details of operating segment revenue for the three and six-month periods ended June 30, 2021 and 2020 are as follows: Three Months Ended Six Months Ended (In millions) 2021 2020 2021 2020 Risk and Insurance Services Marsh $ 2,652 $ 2,168 $ 4,981 $ 4,244 Guy Carpenter 489 435 1,385 1,270 Total Risk and Insurance Services 3,141 2,603 6,366 5,514 Consulting Mercer 1,274 1,149 2,562 2,400 Oliver Wyman Group 618 467 1,203 978 Total Consulting 1,892 1,616 3,765 3,378 Total Operating Segments 5,033 4,219 10,131 8,892 Corporate/Eliminations (16) (30) (31) (52) Total $ 5,017 $ 4,189 $ 10,100 $ 8,840

New Accounting Guidance

New Accounting Guidance	6 Months Ended
	Jun. 30, 2021
Accounting Standards Update and Change in Accounting Principle [Abstract]
New Accounting Guidance	New Accounting Guidance New Accounting Pronouncements Adopted Effective January 1, 2021: In January 2020, the FASB issued guidance that addresses accounting for the transition into and out of the equity method and measuring certain purchased options and forward contracts to acquire investments. The standard takes effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The adoption of this standard did not have a material impact on the Company’s financial position or its results of operations. In December 2019, the FASB issued guidance related to the accounting for income taxes. The standard removes specific exceptions in the current rules and eliminates the need for an organization to analyze whether the following apply in a given period: (a) exception to the incremental approach for intraperiod tax allocation; (b) exceptions to accounting for basis differences when there are ownership changes in foreign investments and (c) exception in interim period income tax accounting for year-to-date losses that exceed anticipated losses. The standard also is designed to improve financial statement preparers’ application of income tax-related guidance and simplify GAAP for (a) franchise taxes that are partially based on income; (b) transactions with a government that result in a step-up in the tax basis of goodwill; (c) separate financial statements of legal entities that are not subject to tax and (d) enacted changes in tax laws in interim periods. The standard takes effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The adoption of this standard did not have a material impact on the Company’s financial position or its results of operations. New Accounting Pronouncements Adopted Effective January 1, 2020: In August 2018, the FASB issued new guidance that amends required fair value measurement disclosures. The guidance adds new requirements, eliminates some current disclosures and modifies other required disclosures. The new disclosure requirements, along with modifications made to disclosures as a result of the change in requirements for narrative descriptions of measurement uncertainty, must be applied on a prospective basis. The effects of all other amendments included in the guidance must be applied retrospectively for all periods presented. The adoption of this guidance impacted disclosures only and did not have an impact on the Company's financial position or results of operations. In January 2017, the FASB issued new guidance to simplify the test for goodwill impairment. The new guidance eliminates the second step in the current two-step goodwill impairment process, under which a goodwill impairment loss is measured by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill for that reporting unit. The new guidance requires a one-step impairment test, in which the goodwill impairment charge is based on the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. The guidance should be applied on a prospective basis with the nature of and reason for the change in accounting principle disclosed upon transition. The adoption of this standard did not have an impact on the Company's financial position or results of operations. In June 2016, the FASB issued new guidance on the impairment of financial instruments. The new guidance adds an allowance for credit losses ("CECL") impairment model that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of lifetime expected credit losses, which the FASB believes will result in more timely recognition of such losses. The new standard is also intended to reduce the complexity of U.S. GAAP by decreasing the number of credit impairment models that entities use to account for debt instruments. Further, the new standard makes targeted changes to the impairment model for available-for-sale debt securities. The adoption of this standard did not have a material impact on the Company’s financial position or results of operations.

Principles of Consolidation a_2

Principles of Consolidation and Other Matters (Policies)	6 Months Ended
	Jun. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
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 United States or as collateral under captive insurance arrangements.
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.
Investments	The caption "Investment income (loss)" 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 that 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 the Company's proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for using the equity method of accounting are included in "other assets" in the consolidated balance sheets.
Income Taxes	The Company's effective tax rate in the second quarter of 2021 was 31.6% compared with 26.2% in the second quarter of 2020. The effective tax rates for the first six months of 2021 and 2020 were 27.9% and 24.9%, respectively. The rate in the second quarter of 2021 reflects the charge of re-measuring the Company’s U.K. deferred tax assets and liabilities upon the enactment of legislation increasing the U.K. corporate income tax rate from 19% to 25%, effective April 1, 2023. This was the most significant discrete item in the second quarter, increasing the Company’s effective tax rate by 8.3% and 4% for the three and six month periods ended June 30, 2020, respectively. The tax rates in both periods reflect 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 and nontaxable adjustments to contingent acquisition consideration. 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 limitation.
Integration and Restructuring Charges	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 right-of-use 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 right-of-use 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 right-of-use asset is determined based on the present value of the estimated net cash flows related to the property. Contractual costs outside of the right-of-use 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 based 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 integration and 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.
Fair Value Measurement	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 as defined by the FASB. 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). Assets and liabilities using Level 2 inputs are related to an equity security. 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 Mutual 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 mutual funds are valued using a valuation technique that results in price per share at $1.00. 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 two
New Accounting Pronouncements	New Accounting Guidance New Accounting Pronouncements Adopted Effective January 1, 2021: In January 2020, the FASB issued guidance that addresses accounting for the transition into and out of the equity method and measuring certain purchased options and forward contracts to acquire investments. The standard takes effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The adoption of this standard did not have a material impact on the Company’s financial position or its results of operations. In December 2019, the FASB issued guidance related to the accounting for income taxes. The standard removes specific exceptions in the current rules and eliminates the need for an organization to analyze whether the following apply in a given period: (a) exception to the incremental approach for intraperiod tax allocation; (b) exceptions to accounting for basis differences when there are ownership changes in foreign investments and (c) exception in interim period income tax accounting for year-to-date losses that exceed anticipated losses. The standard also is designed to improve financial statement preparers’ application of income tax-related guidance and simplify GAAP for (a) franchise taxes that are partially based on income; (b) transactions with a government that result in a step-up in the tax basis of goodwill; (c) separate financial statements of legal entities that are not subject to tax and (d) enacted changes in tax laws in interim periods. The standard takes effect for public business entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2020. The adoption of this standard did not have a material impact on the Company’s financial position or its results of operations. New Accounting Pronouncements Adopted Effective January 1, 2020: In August 2018, the FASB issued new guidance that amends required fair value measurement disclosures. The guidance adds new requirements, eliminates some current disclosures and modifies other required disclosures. The new disclosure requirements, along with modifications made to disclosures as a result of the change in requirements for narrative descriptions of measurement uncertainty, must be applied on a prospective basis. The effects of all other amendments included in the guidance must be applied retrospectively for all periods presented. The adoption of this guidance impacted disclosures only and did not have an impact on the Company's financial position or results of operations. In January 2017, the FASB issued new guidance to simplify the test for goodwill impairment. The new guidance eliminates the second step in the current two-step goodwill impairment process, under which a goodwill impairment loss is measured by comparing the implied fair value of a reporting unit’s goodwill with the carrying amount of that goodwill for that reporting unit. The new guidance requires a one-step impairment test, in which the goodwill impairment charge is based on the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. The guidance should be applied on a prospective basis with the nature of and reason for the change in accounting principle disclosed upon transition. The adoption of this standard did not have an impact on the Company's financial position or results of operations. In June 2016, the FASB issued new guidance on the impairment of financial instruments. The new guidance adds an allowance for credit losses ("CECL") impairment model that is based on expected losses rather than incurred losses. Under the new guidance, an entity recognizes as an allowance its estimate of lifetime expected credit losses, which the FASB believes will result in more timely recognition of such losses. The new standard is also intended to reduce the complexity of U.S. GAAP by decreasing the number of credit impairment models that entities use to account for debt instruments. Further, the new standard makes targeted changes to the impairment model for available-for-sale debt securities. The adoption of this standard did not have a material impact on the Company’s financial position or results of operations.

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2021
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following schedule disaggregates components of the Company's revenue: Three Months Ended Six Months Ended (In millions) 2021 2020 2021 2020 Marsh: EMEA $ 796 $ 597 $ 1,633 $ 1,351 Asia Pacific 347 298 621 536 Latin America 103 99 193 190 Total International 1,246 994 2,447 2,077 U.S./Canada 1,404 1,167 2,528 2,145 Total Marsh 2,650 2,161 4,975 4,222 Guy Carpenter 488 433 1,383 1,260 Subtotal 3,138 2,594 6,358 5,482 Fiduciary interest income 3 9 8 32 Total Risk and Insurance Services $ 3,141 $ 2,603 $ 6,366 $ 5,514 Mercer: Wealth $ 625 $ 561 $ 1,248 $ 1,153 Health 462 432 949 918 Career 187 156 365 329 Total Mercer 1,274 1,149 2,562 2,400 Oliver Wyman Group 618 467 1,203 978 Total Consulting $ 1,892 $ 1,616 $ 3,765 $ 3,378
Contract with Customer, Asset and Liability	The following schedule provides contract assets and contract liabilities information from contracts with customers: (In millions) June 30, 2021 December 31, 2020 Contract assets $ 323 $ 236 Contract liabilities $ 759 $ 676

Per Share Data (Tables)

Per Share Data (Tables)	6 Months Ended
	Jun. 30, 2021
Earnings Per Share [Abstract]
Basic and Diluted EPS Calculation	Basic and Diluted EPS Calculation Three Months Ended Six Months Ended (In millions, except per share amounts) 2021 2020 2021 2020 Net income before non-controlling interests $ 827 $ 580 $ 1,825 $ 1,347 Less: Net income attributable to non-controlling interests 7 8 22 21 Net income attributable to the Company $ 820 $ 572 $ 1,803 $ 1,326 Basic weighted average common shares outstanding 508 506 508 505 Dilutive effect of potentially issuable common shares 5 5 6 5 Diluted weighted average common shares outstanding 513 511 514 510 Average stock price used to calculate common stock equivalents $ 134.04 $ 101.17 $ 124.50 $ 104.14

Supplemental Disclosures to t_2

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Tables)	6 Months Ended
	Jun. 30, 2021
Supplemental Cash Flow Information [Abstract]
Additional Information Concerning Acquisitions, Interest and Income Taxes Paid	The following schedule provides additional information concerning acquisitions, interest and income taxes paid for the six-month periods ended June 30, 2021 and 2020. (In millions) 2021 2020 Assets acquired, excluding cash $ 561 $ 752 Liabilities assumed (60) (29) Contingent/deferred purchase consideration (138) (161) Net cash outflow for current year acquisitions $ 363 $ 562 (In millions) 2021 2020 Interest paid $ 234 $ 248 Income taxes paid, net of refunds $ 403 $ 227

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2021
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes, net of tax, in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the three and six month periods ended June 30, 2021 and 2020, including amounts reclassified out of AOCI, are as follows: (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of April 1, 2021 $ (4,122) $ (1,075) $ (5,197) Other comprehensive (loss) income before reclassifications (16) 24 8 Amounts reclassified from accumulated other comprehensive income 36 — 36 Net current period other comprehensive income 20 24 44 Balance as of June 30, 2021 $ (4,102) $ (1,051) $ (5,153) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of April 1, 2020 $ (3,374) $ (2,473) $ (5,847) Other comprehensive (loss) income before reclassifications (3) 237 234 Amounts reclassified from accumulated other comprehensive income 31 — 31 Net current period other comprehensive income 28 237 265 Balance as of June 30, 2020 $ (3,346) $ (2,236) $ (5,582) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2020 $ (4,126) $ (984) $ (5,110) Other comprehensive loss before reclassifications (52) (67) (119) Amounts reclassified from accumulated other comprehensive income 76 — 76 Net current period other comprehensive income (loss) 24 (67) (43) Balance as of June 30, 2021 $ (4,102) $ (1,051) $ (5,153) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2019 $ (3,512) $ (1,543) $ (5,055) Other comprehensive income (loss) before reclassifications 106 (693) (587) Amounts reclassified from accumulated other comprehensive income 60 — 60 Net current period other comprehensive income (loss) 166 (693) (527) Balance as of June 30, 2020 $ (3,346) $ (2,236) $ (5,582)
Schedule of Components of Comprehensive Income (Loss)	The components of other comprehensive income (loss) for the three and six-month periods ended June 30, 2021 and 2020 are as follows: Three Months Ended June 30, 2021 2020 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 24 $ — $ 24 $ 241 $ 4 $ 237 Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (1) — (1) (1) — (1) Net actuarial losses (a) 52 15 37 40 8 32 Subtotal 51 15 36 39 8 31 Foreign currency translation adjustments (44) (12) (32) (5) (2) (3) Effect of remeasurement 15 1 14 — — — Effect of settlement 2 — 2 — — — Pension/post-retirement plans gains 24 4 20 34 6 28 Other comprehensive income $ 48 $ 4 $ 44 $ 275 $ 10 $ 265 (a) Components of net periodic pension cost are 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. Six Months Ended June 30, 2021 2020 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (67) $ — $ (67) $ (700) $ (7) $ (693) Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (1) — (1) (1) — (1) Net actuarial losses (a) 104 27 77 80 19 61 Subtotal 103 27 76 79 19 60 Foreign currency translation adjustments (81) (20) (61) 130 24 106 Other adjustments (7) (2) (5) — — — Effect of remeasurement 13 1 12 — — — Effect of settlement 2 — 2 — — — Pension/post-retirement plans gains 30 6 24 209 43 166 Other comprehensive (loss) income $ (37) $ 6 $ (43) $ (491) $ 36 $ (527) (a) Components of net periodic pension cost are 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)	6 Months Ended
	Jun. 30, 2021
Business Combination and Asset Acquisition [Abstract]
Schedule For Allocation of Acquisition Costs	The following table presents the preliminary allocation of purchase consideration to the assets acquired and liabilities assumed during 2021 based on the estimated fair values for the acquisitions as of their respective acquisition dates: Acquisitions through June 30, 2021 (In millions) Cash $ 367 Estimated fair value of deferred/contingent consideration 138 Total consideration $ 505 Allocation of purchase price: Cash and cash equivalents $ 4 Accounts receivable, net 30 Other current assets 1 Fixed assets, net 4 Other intangible assets 188 Goodwill 338 Total assets acquired 565 Current liabilities 23 Other liabilities 37 Total liabilities assumed 60 Net assets acquired $ 505
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	The following chart provides information about intangible assets acquired during 2021: Intangible assets through June 30, 2021 (In millions) Amount Weighted Average Amortization Period Client relationships $ 169 14.0 years Other 19 3.9 years $ 188
Pro-Forma Information	The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during 2021 and 2020. In accordance with accounting guidance related to pro-forma disclosures, the information presented for acquisitions made in 2021 is as if they occurred on January 1, 2020 and reflects acquisitions made in 2020 is as if they occurred on January 1, 2019. The unaudited pro-forma information adjusts for the effects of amortization of acquired intangibles. 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 Six Months Ended (In millions, except per share figures) 2021 2020 2021 2020 Revenue $ 5,017 $ 4,231 $ 10,137 $ 8,970 Net income attributable to the Company $ 820 $ 577 $ 1,806 $ 1,332 Basic net income per share attributable to the Company $ 1.61 $ 1.14 $ 3.55 $ 2.64 Diluted net income per share attributable to the Company $ 1.60 $ 1.13 $ 3.52 $ 2.61

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	6 Months Ended
	Jun. 30, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the Carrying Amount of Goodwill	Changes in the carrying amount of goodwill are as follows: June 30, (In millions) 2021 2020 Balance as of January 1, $ 15,517 $ 14,671 Goodwill acquired 338 466 Other adjustments (a) (80) (340) Balance at June 30, $ 15,775 $ 14,797 (a) Primarily reflects the impact of foreign exchange.
Amortized Intangible Assets	The gross cost and accumulated amortization of identified intangible assets at June 30, 2021 and December 31, 2020 are as follows: June 30, 2021 December 31, 2020 (In millions) Gross Accumulated Net Gross Accumulated Net Client relationships $ 3,882 $ 1,320 $ 2,562 $ 3,713 $ 1,170 $ 2,543 Other (a) 407 252 155 386 230 156 Amortized intangibles $ 4,289 $ 1,572 $ 2,717 $ 4,099 $ 1,400 $ 2,699 (a) Primarily non-compete agreements, trade names and developed technology.
Estimated Future Aggregate Amortization Expense	The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2021 (excludes amortization through June 30, 2021) $ 182 2022 337 2023 309 2024 289 2025 251 Subsequent years 1,349 $ 2,717

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2021
Fair Value Disclosures [Abstract]
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 as of June 30, 2021 and December 31, 2020: Identical Assets Observable Inputs Unobservable Total (In millions) 06/30/21 12/31/20 06/30/21 12/31/20 06/30/21 12/31/20 06/30/21 12/31/20 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 63 $ 59 $ — $ — $ — $ — $ 63 $ 59 Mutual funds (a) 186 186 — — — — 186 186 Money market funds (b) 75 587 — — — — 75 587 Other equity investment (a) — — 8 8 — — 8 8 Contingent purchase consideration assets (c) — — — — 6 68 6 68 Total assets measured at fair value $ 324 $ 832 $ 8 $ 8 $ 6 $ 68 $ 338 $ 908 Fiduciary Assets: U.S. treasury bills $ — $ 150 $ — $ — $ — $ — $ — $ 150 Money market funds 243 173 — — — — 243 173 Total fiduciary assets measured $ 243 $ 323 $ — $ — $ — $ — $ 243 $ 323 Liabilities: Contingent purchase consideration liability (d) $ — $ — $ — $ — $ 340 $ 243 $ 340 $ 243 Total liabilities measured at fair value $ — $ — $ — $ — $ 340 $ 243 $ 340 $ 243 (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.
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 six month periods ended June 30, 2021 and 2020: Three Months Ended Six Months Ended (In millions) 2021 2020 2021 2020 Balance at beginning of period $ 233 $ 239 $ 243 $ 225 Net additions 97 66 97 96 Payments (6) (65) (17) (78) Revaluation impact 16 (11) 17 (10) Other (a) — 4 — — Balance at June 30, $ 340 $ 233 $ 340 $ 233 (a) Primarily reflects the impact of foreign exchange.

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2021
Leases [Abstract]
Lease Cost and Additional Information	The following chart provides additional information about the Company’s property leases: Three Months Ended June 30, Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Lease Cost: Operating lease cost $ 95 $ 97 $ 189 $ 189 Short-term lease cost 2 1 3 2 Variable lease cost 26 27 63 64 Sublease income (5) (5) (13) (10) Net lease cost $ 118 $ 120 $ 242 $ 245 Other information: Operating cash outflows from operating leases $ 204 $ 197 Right of use assets obtained in exchange for new operating lease liabilities $ 251 $ 129 Weighted-average remaining lease term – real estate 9.1 years 8.5 years Weighted-average discount rate – real estate leases 2.76 % 3.05 %
Future Minimum Lease Payments for Operating Leases	Future minimum lease payments for the Company’s operating leases as of June 30, 2021 are as follows: Payment Dates (In millions) Real Estate Leases Remainder of 2021 $ 208 2022 388 2023 340 2024 297 2025 265 2026 244 Subsequent years 901 Total future lease payments 2,643 Less: Imputed interest (309) Total $ 2,334 Current lease liabilities $ 342 Long-term lease liabilities 1,992 Total lease liabilities $ 2,334 Note: Table excludes obligations for leases with original terms of 12 months or less which have not been recognized as a right of use asset or liability in the consolidated balance sheets.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	6 Months Ended
	Jun. 30, 2021
Retirement Benefits [Abstract]
Schedule of Net Benefit Costs	The components of the net periodic benefit cost for defined benefit and other post-retirement plans are as follows: Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 10 $ 9 $ — $ — Interest cost 86 104 1 — Expected return on plan assets (211) (207) — — Recognized actuarial loss 51 40 — — Net periodic benefit (credit) cost $ (64) $ (54) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (62) $ (54) $ 1 $ — Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 20 $ 17 $ — $ — Interest cost 171 210 1 1 Expected return on plan assets (419) (417) — — Amortization of prior service credit — — (1) (1) Recognized actuarial loss 103 80 1 — Net periodic benefit (credit) cost $ (125) $ (110) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (123) $ (110) $ 1 $ — Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Compensation and benefits expense $ 10 $ 9 $ — $ — Other net benefit (credit) cost (72) (63) 1 — Total (credit) cost $ (62) $ (54) $ 1 $ — Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Compensation and benefits expense $ 20 $ 17 $ — $ — Other net benefit (credit) cost (143) (127) 1 — Total (credit) cost $ (123) $ (110) $ 1 $ — U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Interest cost $ 46 $ 54 $ — $ — Expected return on plan assets (81) (87) — — Recognized actuarial loss 22 18 — — Net periodic benefit credit $ (13) $ (15) $ — $ — U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Interest cost $ 92 $ 107 $ — $ — Expected return on plan assets (163) (173) — — Recognized actuarial loss 45 36 — — Net periodic benefit credit $ (26) $ (30) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 10 $ 9 $ — $ — Interest cost 40 50 1 — Expected return on plan assets (130) (120) — — Recognized actuarial loss 29 22 — — Net periodic benefit (credit) cost $ (51) $ (39) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (49) $ (39) $ 1 $ — Significant non-U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2021 2020 2021 2020 Service cost $ 20 $ 17 $ — $ — Interest cost 79 103 1 1 Expected return on plan assets (256) (244) — — Amortization of prior service credit — — (1) (1) Recognized actuarial loss 58 44 1 — Net periodic benefit (credit) cost $ (99) $ (80) $ 1 $ — Settlement loss 2 — — — Total (credit) cost $ (97) $ (80) $ 1 $ —
Schedule of Assumptions Used	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 Post-retirement June 30, 2021 2020 2021 2020 Weighted average assumptions: Expected return on plan assets 4.72 % 5.31 % — — Discount rate 1.92 % 2.57 % 2.42 % 2.72 % Rate of compensation increase 1.85 % 1.76 % — —

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2021
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	The Company’s outstanding debt is as follows: (In millions) June 30, December 31, Short-term: Current portion of long-term debt $ 516 $ 517 516 517 Long-term: Senior notes – 4.80% due 2021 — 500 Senior notes – 2.75% due 2022 499 499 Senior notes – 3.30% due 2023 349 349 Senior notes – 4.05% due 2023 249 249 Senior notes – 3.50% due 2024 598 598 Senior notes – 3.875% due 2024 996 995 Senior notes – 3.50% due 2025 498 498 Senior notes – 1.349% due 2026 660 677 Senior notes – 3.75% due 2026 598 597 Senior notes – 4.375% due 2029 1,499 1,499 Senior notes – 1.979% due 2030 645 664 Senior notes – 2.250% due 2030 738 737 Senior notes – 5.875% due 2033 298 298 Senior notes – 4.75% due 2039 495 495 Senior notes – 4.35% due 2047 493 493 Senior notes – 4.20% due 2048 592 592 Senior notes – 4.90% due 2049 1,237 1,237 Mortgage – 5.70% due 2035 324 331 Other 5 5 10,773 11,313 Less current portion 516 517 $ 10,257 $ 10,796
Estimated Fair Value Of Significant Financial Instruments	The following table reflects the carrying values and estimated fair value of the Company’s short-term and long-term debt. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts 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. June 30, 2021 December 31, 2020 (In millions) Carrying Fair Carrying Fair Short-term debt $ 516 $ 523 $ 517 $ 523 Long-term debt $ 10,257 $ 11,853 $ 10,796 $ 12,858

Restructuring Costs (Tables)

Restructuring Costs (Tables)	6 Months Ended
	Jun. 30, 2021
Restructuring and Related Activities [Abstract]
Restructuring Activities	Details of the JLT integration and restructuring activity from January 1, 2020 through June 30, 2021, are as follows: (In millions) Severance Real Estate Related Costs (a) Information Technology (a) Consulting and Other Outside Services (b) Total Liability at 1/1/20 $ 42 $ 5 $ — $ — $ 47 2020 charges 43 69 62 77 251 Cash payments (69) (25) (55) (77) (226) Non-cash charges — (42) (5) — (47) Liability at 12/31/20 $ 16 $ 7 $ 2 $ — $ 25 2021 charges 4 12 11 15 42 Cash payments (9) (7) (13) (15) (44) Non-cash charges — (8) — — (8) Liability at 6/30/21 $ 11 $ 4 $ — $ — $ 15 (a) Includes ROU asset impairments, data center contract termination costs and temporary infrastructure leasing costs. (b) Includes consulting fees related to the management of the integration processes and legal fees related to the rationalization of legal entity structures. The following details other restructuring liabilities for actions initiated prior to 2021: (In millions) Liability at Amounts Cash Non-Cash/Other Liability at 12/31/20 Amounts Cash Non-Cash/Other Liability at 6/30/21 Severance $ 51 $ 39 $ (54) $ — $ 36 $ 9 $ (28) $ — $ 17 Future rent under non-cancelable leases and other costs 51 50 (46) (10) 45 14 (19) (2) 38 Total $ 102 $ 89 $ (100) $ (10) $ 81 $ 23 $ (47) $ (2) $ 55

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2021
Segment Reporting [Abstract]
Selected Information And Details For MMC's Operating Segments	Selected information about the Company’s operating segments for the three and six month periods ended June 30, 2021 and 2020 are as follows: Three Months Ended Six Months Ended (In millions) Revenue Operating Income Revenue Operating Income 2021– Risk and Insurance Services $ 3,141 (a) $ 950 $ 6,366 (c) $ 2,010 Consulting 1,892 (b) 344 3,765 (d) 705 Total Operating Segments 5,033 1,294 10,131 2,715 Corporate/Eliminations (16) (66) (31) (129) Total Consolidated $ 5,017 $ 1,228 $ 10,100 $ 2,586 2020– Risk and Insurance Services $ 2,603 (a) $ 696 $ 5,514 (c) $ 1,550 Consulting 1,616 (b) 255 3,378 (d) 537 Total Operating Segments 4,219 951 8,892 2,087 Corporate/Eliminations (30) (66) (52) (132) Total Consolidated $ 4,189 $ 885 $ 8,840 $ 1,955 (a) Includes inter-segment revenue of $4 million in both 2021 and 2020, interest income on fiduciary funds of $3 million and $9 million in 2021 and 2020, respectively, and equity method income of $14 million in both 2021 and 2020. (b) Includes inter-segment revenue of $12 million and $26 million in 2021 and 2020, respectively. (c) Includes inter-segment revenue of $4 million and $5 million in 2021 and 2020, respectively, interest income on fiduciary funds of $8 million and $32 million in 2021 and 2020, respectively, and equity method income of $17 million and $13 million in 2021 and 2020, respectively. (d) Includes inter-segment revenue of $27 million and $47 million in 2021 and 2020, respectively, and equity method income of $4 million in 2020 and none in 2021.
Details of Operating Segment Revenue	Details of operating segment revenue for the three and six-month periods ended June 30, 2021 and 2020 are as follows: Three Months Ended Six Months Ended (In millions) 2021 2020 2021 2020 Risk and Insurance Services Marsh $ 2,652 $ 2,168 $ 4,981 $ 4,244 Guy Carpenter 489 435 1,385 1,270 Total Risk and Insurance Services 3,141 2,603 6,366 5,514 Consulting Mercer 1,274 1,149 2,562 2,400 Oliver Wyman Group 618 467 1,203 978 Total Consulting 1,892 1,616 3,765 3,378 Total Operating Segments 5,033 4,219 10,131 8,892 Corporate/Eliminations (16) (30) (31) (52) Total $ 5,017 $ 4,189 $ 10,100 $ 8,840

Nature of Operations (Details)

Nature of Operations (Details)	6 Months Ended
	Jun. 30, 2021segment
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 ($)	Jun. 10, 2021	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Revenue reduction for estimated commission revenue			$ 36,000,000
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements		$ 304,000,000		$ 304,000,000		$ 270,000,000
Equity method investments lag period				3 months
Gain (loss) on investment income, net		$ 19,000,000	$ (31,000,000)	$ 30,000,000	$ (33,000,000)
Charge related to revaluation of deferred tax assets and liabilities	$ 100,000,000
Effective tax rate (as a percent)		31.60%	26.20%	27.90%	24.90%
Increase in effective tax rate due to change in U.K. corporate income tax rate, percent		8.30%		4.00%
Unrecognized tax benefits		$ 94,000,000		$ 94,000,000		$ 98,000,000
Minimum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits		0		0
Maximum
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Reasonably possible decrease in unrecognized tax benefits		$ 33,000,000		$ 33,000,000
Alexander Forbes Group Holdings Limited
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Gain (loss) on investment income, net			$ (23,000,000)		$ (23,000,000)

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 5,017	$ 4,189	$ 10,100	$ 8,840
Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	3,141	2,603	6,366	5,514
Fiduciary interest income	3	9	8	32
Risk and Insurance Services Segment | Total International
Disaggregation of Revenue [Line Items]
Revenue	1,246	994	2,447	2,077
Risk and Insurance Services Segment | EMEA
Disaggregation of Revenue [Line Items]
Revenue	796	597	1,633	1,351
Risk and Insurance Services Segment | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	347	298	621	536
Risk and Insurance Services Segment | Latin America
Disaggregation of Revenue [Line Items]
Revenue	103	99	193	190
Risk and Insurance Services Segment | U.S./Canada
Disaggregation of Revenue [Line Items]
Revenue	1,404	1,167	2,528	2,145
Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,892	1,616	3,765	3,378
Consulting Segment | Wealth
Disaggregation of Revenue [Line Items]
Revenue	625	561	1,248	1,153
Consulting Segment | Health
Disaggregation of Revenue [Line Items]
Revenue	462	432	949	918
Consulting Segment | Career
Disaggregation of Revenue [Line Items]
Revenue	187	156	365	329
Marsh & Guy Carpenter | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	3,138	2,594	6,358	5,482
Marsh Insurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	2,650	2,161	4,975	4,222
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	488	433	1,383	1,260
Mercer Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,274	1,149	2,562	2,400
Oliver Wyman Group Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 618	$ 467	$ 1,203	$ 978

Revenue - Contract Assets and C

Revenue - Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Contract assets	$ 323	$ 236
Contract liabilities	$ 759	$ 676

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Disaggregation of Revenue [Line Items]
Revenue recognized that was included in the contract liability balance at the beginning of the period	$ 380	$ 418
Performance obligation satisfied in previous period	72	$ 67
Marsh Insurance Group
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	56
Mercer Consulting Group
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	178
Oliver Wyman Group Consulting Group
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	$ 1

Revenue - Estimated Revenue Exp

Revenue - Estimated Revenue Expected to Be Recognized Related to Performance Obligations (Details) $ in Millions	Jun. 30, 2021USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 128
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 68
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 28
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2025-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 8
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2026-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 3
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)

Fiduciary Assets and Liabilit_2

Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 14,200		$ 14,200		$ 11,200
Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	3	$ 9	8	$ 32
Operating Segments | Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	$ 3	$ 9	$ 8	$ 32

Per Share Data (Basic and Dilut

Per Share Data (Basic and Diluted EPS Calculation Continuing Operations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Earnings Per Share [Abstract]
Net income before non-controlling interests	$ 827	$ 580	$ 1,825	$ 1,347
Less: Net income attributable to non-controlling interests	7	8	22	21
Net income attributable to the Company	$ 820	$ 572	$ 1,803	$ 1,326
Basic weighted average common shares outstanding (in shares)	508	506	508	505
Dilutive effect of potentially issuable common shares (in shares)	5	5	6	5
Diluted weighted average common shares outstanding (in shares)	513	511	514	510
Average stock price used to calculate common stock equivalents (in dollars per share)	$ 134.04	$ 101.17	$ 124.50	$ 104.14

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	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Supplemental Cash Flow Information [Abstract]
Assets acquired, excluding cash	$ 561	$ 752
Liabilities assumed	(60)	(29)
Contingent/deferred purchase consideration	(138)	(161)
Net cash outflow for current year acquisitions	363	562
Interest paid	234	248
Income taxes paid, net of refunds	$ 403	$ 227

Supplemental Disclosures to t_4

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 97	$ 69
Deferred purchase consideration from prior years' acquisitions	84	27
Contingent consideration from prior year's acquisitions	13	42
Contingent consideration from prior year's dispositions	71
Credit adjustment related to contingent consideration liabilities	17	6
Payment of contingent consideration	4	36
Adjustments related to contingent consideration receivable	24
Proceeds from contingent consideration, prior period dispositions	18
Non-cash issuance of common stock	228	213
Stock-based compensation expense, equity awards	$ 176	$ 147

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			$ 9,260
Other comprehensive income (loss), net of tax	$ 44	$ 265	(43)	$ (527)
Balance, end of period	10,264	8,392	10,264	8,392
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(5,197)	(5,847)	(5,110)	(5,055)
Other comprehensive income (loss), before reclassification, net of tax	8	234	(119)	(587)
Amounts reclassified from accumulated other comprehensive income	36	31	76	60
Other comprehensive income (loss), net of tax	44	265	(43)	(527)
Balance, end of period	(5,153)	(5,582)	(5,153)	(5,582)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(4,122)	(3,374)	(4,126)	(3,512)
Other comprehensive income (loss), before reclassification, net of tax	(16)	(3)	(52)	106
Amounts reclassified from accumulated other comprehensive income	36	31	76	60
Other comprehensive income (loss), net of tax	20	28	24	166
Balance, end of period	(4,102)	(3,346)	(4,102)	(3,346)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(1,075)	(2,473)	(984)	(1,543)
Other comprehensive income (loss), before reclassification, net of tax	24	237	(67)	(693)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	24	237	(67)	(693)
Balance, end of period	$ (1,051)	$ (2,236)	$ (1,051)	$ (2,236)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) (Schedule Of Components Of Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before tax	$ 48	$ 275	$ (37)	$ (491)
Other comprehensive income (loss), tax	4	10	6	36
Other comprehensive income (loss), net of tax	44	265	(43)	(527)
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassification, before tax	24	241	(67)	(700)
Other comprehensive income (loss), before reclassification, tax	0	4	0	(7)
Other comprehensive income (loss), before reclassification, net of tax	24	237	(67)	(693)
Reclassification from AOCI, net of tax	0	0	0	0
Other comprehensive income (loss), net of tax	24	237	(67)	(693)
Pension/Post-Retirement Plans Gains (Losses)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassification, net of tax	(16)	(3)	(52)	106
Reclassification from AOCI, before Tax	51	39	103	79
Reclassification from AOCI, tax	15	8	27	19
Reclassification from AOCI, net of tax	36	31	76	60
Other comprehensive income (loss), before tax	24	34	30	209
Other comprehensive income (loss), tax	4	6	6	43
Other comprehensive income (loss), net of tax	20	28	24	166
Prior service credits
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	(1)	(1)	(1)	(1)
Reclassification from AOCI, tax	0	0	0	0
Reclassification from AOCI, net of tax	(1)	(1)	(1)	(1)
Net actuarial losses
Accumulated Other Comprehensive Income (Loss) [Line Items]
Reclassification from AOCI, before Tax	52	40	104	80
Reclassification from AOCI, tax	15	8	27	19
Reclassification from AOCI, net of tax	37	32	77	61
Foreign currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassification, before tax	(44)	(5)	(81)	130
Other comprehensive income (loss), before reclassification, tax	(12)	(2)	(20)	24
Other comprehensive income (loss), before reclassification, net of tax	(32)	(3)	(61)	106
Other adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassification, before tax			(7)	0
Other comprehensive income (loss), before reclassification, tax			(2)	0
Other comprehensive income (loss), before reclassification, net of tax			(5)	0
Effect of remeasurement
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassification, before tax	15	0	13	0
Other comprehensive income (loss), before reclassification, tax	1	0	1	0
Other comprehensive income (loss), before reclassification, net of tax	14	0	12	0
Effect of settlement
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other comprehensive income (loss), before reclassification, before tax	2	0	2	0
Other comprehensive income (loss), before reclassification, tax	0	0	0	0
Other comprehensive income (loss), before reclassification, net of tax	$ 2	$ 0	$ 2	$ 0

Acquisitions and Dispositions_2

Acquisitions and Dispositions (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2021USD ($)acquisition	Jun. 30, 2020USD ($)	Dec. 31, 2020acquisition
Business Acquisition [Line Items]
Total consideration			$ 505	$ 737
Cash paid			367	576
Deferred purchase consideration from prior years' acquisitions			84	27
Estimated fair value of deferred/contingent consideration			138	161
Contingent consideration from prior year's acquisitions			13	42
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration			505
Cash paid			367
Estimated fair value of deferred/contingent consideration			138
Revenue related to acquisitions	$ 35		35
Operating income related to acquisitions	$ 2		2
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions				27
Estimated fair value of deferred/contingent consideration			$ 17
Revenue related to acquisitions		$ 48		63
Operating income related to acquisitions		$ 7		11
Contingent consideration from prior year's acquisitions				78
Risk and Insurance Services Segment
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition			2		7
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)			2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)			4 years
Certain Businesses Primarily in the U.S., U.K. and Canada
Business Acquisition [Line Items]
Disposal group, consideration			$ 81	$ 93
Gain on disposal			$ 50

Acquisitions and Dispositions_3

Acquisitions and Dispositions (Allocation Of Acquisition Costs) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Business Acquisition [Line Items]
Cash	$ 367	$ 576
Estimated fair value of deferred/contingent consideration	138	161
Total consideration	505	737
Allocation of purchase price:
Goodwill	15,775	$ 14,797	$ 15,517	$ 14,671
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	367
Estimated fair value of deferred/contingent consideration	138
Total consideration	505
Allocation of purchase price:
Cash and cash equivalents	4
Accounts receivable, net	30
Other current assets	1
Fixed assets, net	4
Other intangible assets	188
Goodwill	338
Total assets acquired	565
Current liabilities	23
Other liabilities	37
Total liabilities assumed	60
Net assets acquired	$ 505

Acquisitions and Dispositions_4

Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 188
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 169
Finite-lived intangible assets, remaining amortization period	14 years
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 19
Finite-lived intangible assets, remaining amortization period	3 years 10 months 24 days

Acquisitions and Dispositions_5

Acquisitions and Dispositions (Pro-Forma Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Business Combination and Asset Acquisition [Abstract]
Revenue	$ 5,017	$ 4,231	$ 10,137	$ 8,970
Net income attributable to the Company	$ 820	$ 577	$ 1,806	$ 1,332
Basic net income per share attributable to the Company (in dollars per share)	$ 1.61	$ 1.14	$ 3.55	$ 2.64
Diluted net income per share attributable to the Company (in dollars per share)	$ 1.60	$ 1.13	$ 3.52	$ 2.61

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Goodwill [Roll Forward]
Balance as of January 1,	$ 15,517	$ 14,671
Goodwill acquired	338	466
Other adjustments	(80)	(340)
Balance at June 30,	$ 15,775	$ 14,797

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Goodwill acquired			$ 338	$ 466
Goodwill, expected tax deductible amount	$ 1	$ 141	1	141
Goodwill	15,775	14,797	15,775	14,797	$ 15,517	$ 14,671
Aggregate amortization expense	189	$ 174	189	$ 174
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill	11,900		11,900
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	$ 3,900		$ 3,900

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Finite-Lived Intangible Assets [Line Items]
Gross Cost	$ 4,289	$ 4,099
Accumulated Amortization	1,572	1,400
Net Carrying Amount	2,717	2,699
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost	3,882	3,713
Accumulated Amortization	1,320	1,170
Net Carrying Amount	2,562	2,543
Other
Finite-Lived Intangible Assets [Line Items]
Gross Cost	407	386
Accumulated Amortization	252	230
Net Carrying Amount	$ 155	$ 156

Goodwill And Other Intangible_5

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Goodwill and Intangible Assets Disclosure [Abstract]
2021 (excludes amortization through June 30, 2021)	$ 182
2022	337
2023	309
2024	289
2025	251
Subsequent years	1,349
Net Carrying Amount	$ 2,717	$ 2,699

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	May 31, 2020	Feb. 29, 2020	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment			$ 315		$ 315		$ 280
Equity securities			76		76		72
Equity investments without readily determinable market value			34		34		33
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from contingent purchase consideration, asset					$ 89
Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period (in years)					2 years
Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Revenue target period (in years)					4 years
Private Insurance and Consulting
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment			175		$ 175		169
Private Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment			140		140		111
Equity method income (loss)			17	$ (6)	27	$ (7)
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, fair value			$ 58		$ 58		$ 54
Number of shares sold (shares)	193	49
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount)			$ 1		$ 1

Fair Value Measurements (Assets

Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Financial instruments owned:
Exchange traded equity securities	$ 76	$ 72
Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	338	908
Fiduciary Assets:
Fiduciary assets	243	323
Liabilities:
Total liabilities measured at fair value	340	243
Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	324	832
Fiduciary Assets:
Fiduciary assets	243	323
Liabilities:
Total liabilities measured at fair value	0	0
Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	8	8
Fiduciary Assets:
Fiduciary assets	0	0
Liabilities:
Total liabilities measured at fair value	0	0
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	6	68
Fiduciary Assets:
Fiduciary assets	0	0
Liabilities:
Total liabilities measured at fair value	340	243
US Treasury Bills | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	150
US Treasury Bills | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	150
US Treasury Bills | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	0
US Treasury Bills | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	0
Money Market Funds | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	243	173
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	243	173
Money Market Funds | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	0
Money Market Funds | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	0
Other Assets | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	63	59
Mutual funds	186	186
Other equity investments	8	8
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	63	59
Mutual funds	186	186
Other equity investments	0	0
Other Assets | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Other equity investments	8	8
Other Assets | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	0	0
Mutual funds	0	0
Other equity investments	0	0
Cash and Cash Equivalents | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	75	587
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	75	587
Cash and Cash Equivalents | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	0	0
Cash and Cash Equivalents | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	0	0
Other Receivables | Fair Value, Measurements, Recurring
Financial instruments owned:
Contingent purchase consideration asset	6	68
Other Receivables | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Contingent purchase consideration asset	0	0
Other Receivables | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Financial instruments owned:
Contingent purchase consideration asset	0	0
Other Receivables | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Contingent purchase consideration asset	6	68
Accounts Payable and Accrued Liabilities and Other Liabilities | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	340	243
Accounts Payable and Accrued Liabilities and Other Liabilities | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	$ 340	$ 243

Fair Value Measurements (Change

Fair Value Measurements (Changes In Fair Value Of Level 3 Liabilities Representing Acquisition Related Contingent Consideration) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Revaluation impact			$ 17	$ 6
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 233	$ 239	243	225
Net additions	97	66	97	96
Payments	(6)	(65)	(17)	(78)
Revaluation impact	16	(11)	17	(10)
Other	0	4	0	0
Balance at June 30,	$ 340	$ 233	$ 340	$ 233

Derivatives (Narrative) (Detail

Derivatives (Narrative) (Details) - 6 months ended Jun. 30, 2021 $ in Millions	USD ($)	EUR (€)
Derivative [Line Items]
Net investment hedge, threshold percentage of the equity balance	80.00%
Decrease in net investment hedges | $	$ 36
Net Investment Hedging
Derivative [Line Items]
Derivative, notional amount | €		€ 1,100,000,000

Leases (Narrative) (Details)

Leases (Narrative) (Details)	6 Months Ended
	Jun. 30, 2021
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (years)	10 years
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (years)	25 years
Office Space
Lessee, Lease, Description [Line Items]
Lease obligations, percent	99.00%

Leases (Lease Cost and Addition

Leases (Lease Cost and Additional Information) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 95	$ 97	$ 189	$ 189
Short-term lease cost	2	1	3	2
Variable lease cost	26	27	63	64
Sublease income	(5)	(5)	(13)	(10)
Net lease cost	$ 118	$ 120	242	245
Operating cash outflows from operating leases			204	197
Right of use assets obtained in exchange for new operating lease liabilities			$ 251	$ 129
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	9 years 1 month 6 days	8 years 6 months	9 years 1 month 6 days	8 years 6 months
Weighted-average discount rate, percent	2.76%	3.05%	2.76%	3.05%

Leases (Future Minimum Payments

Leases (Future Minimum Payments for Operating Leases) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Remainder of 2021	$ 208
2022	388
2023	340
2024	297
2025	265
2026	244
Subsequent years	901
Total future lease payments	2,643
Less: Imputed interest	(309)
Total	2,334
Current lease liabilities	342	$ 342
Long-term lease liabilities	$ 1,992	$ 1,924

Retirement Benefits (Narrative)

Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer		$ 57
Estimated future employer contributions in current fiscal year		72
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		78	$ 73
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized		$ 73	$ 64
United Kingdom | Non-U.S. Plans | Geographic Concentration Risk
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage	81.00%
Equity Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		64.00%
Actual asset allocation percentage of equity		65.00%
Equity Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		27.00%
Actual asset allocation percentage of equity		29.00%
Fixed Income Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		36.00%
Actual asset allocation percentage of equity		35.00%
Fixed Income Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage		73.00%
Actual asset allocation percentage of equity		71.00%

Retirement Benefits (Schedule O

Retirement Benefits (Schedule Of Defined Benefit Plan Net Periodic Benefit Cost Combined U.S. and Significant Non-U.S. Plans) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 9	$ 20	$ 17
Interest cost	86	104	171	210
Expected return on plan assets	(211)	(207)	(419)	(417)
Amortization of prior service (credit) cost			0	0
Recognized actuarial loss	51	40	103	80
Net periodic benefit (credit) cost	(64)	(54)	(125)	(110)
Settlement loss	2	0	2	0
Total (credit) cost	(62)	(54)	(123)	(110)
Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Interest cost	46	54	92	107
Expected return on plan assets	(81)	(87)	(163)	(173)
Recognized actuarial loss	22	18	45	36
Net periodic benefit (credit) cost	(13)	(15)	(26)	(30)
Pension Benefits | Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	9	20	17
Interest cost	40	50	79	103
Expected return on plan assets	(130)	(120)	(256)	(244)
Amortization of prior service (credit) cost			0	0
Recognized actuarial loss	29	22	58	44
Net periodic benefit (credit) cost	(51)	(39)	(99)	(80)
Settlement loss	2	0	2	0
Total (credit) cost	(49)	(39)	(97)	(80)
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service (credit) cost			(1)	(1)
Recognized actuarial loss	0	0	1	0
Net periodic benefit (credit) cost	1	0	1	0
Settlement loss	0	0	0	0
Total (credit) cost	1	0	1	0
Post-retirement Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Interest cost	0	0	0	0
Expected return on plan assets	0	0	0	0
Recognized actuarial loss	0	0	0	0
Net periodic benefit (credit) cost	0	0	0	0
Post-retirement Benefits | Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service (credit) cost			(1)	(1)
Recognized actuarial loss	0	0	1	0
Net periodic benefit (credit) cost	1	0	1	0
Settlement loss	0	0	0	0
Total (credit) cost	$ 1	$ 0	$ 1	$ 0

Retirement Benefits (Schedule_2

Retirement Benefits (Schedule Of Defined Benefit Plan Net Periodic Benefit Cost Amounts Recorded in Consolidated Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	$ (1,228)	$ (885)	$ (2,586)	$ (1,955)
Other net benefit (credits) cost	(71)	(63)	(142)	(127)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	10	9	20	17
Other net benefit (credits) cost	(72)	(63)	(143)	(127)
Total (credit) cost	(62)	(54)	(123)	(110)
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	0	0	0	0
Other net benefit (credits) cost	1	0	1	0
Total (credit) cost	$ 1	$ 0	$ 1	$ 0

Retirement Benefits (Schedule_3

Retirement Benefits (Schedule Of Defined Benefit Plan Weighted Average Assumption Used In Calculating Net Periodic Benefit Cost) (Details)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
Pension Benefits
Weighted average assumptions:
Expected return on plan assets	4.72%	5.31%
Discount rate	1.92%	2.57%
Rate of compensation increase	1.85%	1.76%
Post-retirement Benefits
Weighted average assumptions:
Expected return on plan assets	0.00%	0.00%
Discount rate	2.42%	2.72%
Rate of compensation increase	0.00%	0.00%

Debt (Schedule Of Outstanding D

Debt (Schedule Of Outstanding Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Current portion of long-term debt	$ 516	$ 517
Short-term debt	516	517
Long-term debt	10,773	11,313
Long-term debt, net	10,257	10,796
4.80% Senior Debt Obligations Due 2021
Debt Instrument [Line Items]
Long-term debt	$ 0	500
Interest rate	4.80%
2.75% Senior Debt Obligations Due 2022
Debt Instrument [Line Items]
Long-term debt	$ 499	499
Interest rate	2.75%
3.30% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Long-term debt	$ 349	349
Interest rate	3.30%
4.05% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Long-term debt	$ 249	249
Interest rate	4.05%
3.50% Senior Debt Obligations Due 2024
Debt Instrument [Line Items]
Long-term debt	$ 598	598
Interest rate	3.50%
3.875% Senior Debt Obligations Due 2024
Debt Instrument [Line Items]
Long-term debt	$ 996	995
Interest rate	3.875%
3.50% Senior Debt Obligations Due 2025
Debt Instrument [Line Items]
Long-term debt	$ 498	498
Interest rate	3.50%
1.349% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 660	677
Interest rate	1.349%
3.75% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 598	597
Interest rate	3.75%
4.375% Senior Debt Obligations Due 2029
Debt Instrument [Line Items]
Long-term debt	$ 1,499	1,499
Interest rate	4.375%
1.979% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Long-term debt	$ 645	664
Interest rate	1.979%
2.250% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Long-term debt	$ 738	737
Interest rate	2.25%
5.875% Senior Debt Obligations Due 2033
Debt Instrument [Line Items]
Long-term debt	$ 298	298
Interest rate	5.875%
4.75% Senior Debt Obligations Due 2039
Debt Instrument [Line Items]
Long-term debt	$ 495	495
Interest rate	4.75%
4.35% Senior Debt Obligation Due 2047
Debt Instrument [Line Items]
Long-term debt	$ 493	493
Interest rate	4.35%
4.20% Senior Debt Obligations Due 2048
Debt Instrument [Line Items]
Long-term debt	$ 592	592
Interest rate	4.20%
4.90% Senior Debt Obligations Due 2049
Debt Instrument [Line Items]
Long-term debt	$ 1,237	1,237
Interest rate	4.90%
5.70% Mortgage Due 2035
Debt Instrument [Line Items]
Long-term debt	$ 324	331
Interest rate	5.70%
Other
Debt Instrument [Line Items]
Long-term debt	$ 5	$ 5

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($)	Apr. 15, 2021	Apr. 02, 2021	Mar. 31, 2020	Jan. 31, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020	Apr. 09, 2021	Apr. 08, 2021	Dec. 31, 2020	May 31, 2020
Debt Instrument [Line Items]
Commercial paper outstanding						$ 0
Proceeds from lines of credit						0	$ 1,000,000,000
Other Debt Facilities
Debt Instrument [Line Items]
Long-term line of credit						0				$ 0
Debt instrument, unused borrowing capacity						511,000,000				$ 573,000,000
Commercial Paper
Debt Instrument [Line Items]
Short-term debt								$ 2,000,000,000	$ 1,500,000,000
Revolving Credit Facility | New Facility
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity		$ 2,800,000,000
Term of debt		5 years
Long-term line of credit						0
Revolving Credit Facility | Old Facility
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity						$ 1,800,000,000
Term of debt						5 years
Revolving Credit Facility | 364-day Facility
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity						$ 1,000,000,000
Term of debt						364 days
Term Loan Facility | $500 Million One-Year Term Loan and $500 Million Two-Year Term Loan
Debt Instrument [Line Items]
Proceeds from lines of credit					$ 1,000,000,000
Term Loan Facility | $500 Million One-Year Term Loan Facility
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity				$ 500,000,000
Term of debt				1 year
Term Loan Facility | $500 Million Two-Year Term Loan Facility
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity				$ 500,000,000
Term of debt				2 years
Senior Notes
Debt Instrument [Line Items]
Repayments of debt	$ 500,000,000		$ 500,000,000
Senior Notes | 2.250% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Debt instrument face amount											$ 750,000,000

Debt (Estimated Fair Value of S

Debt (Estimated Fair Value of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 516	$ 517
Long-term debt	10,257	10,796
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	523	523
Long-term debt	$ 11,853	$ 12,858

Restructuring Costs (Narrative)

Restructuring Costs (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Restructuring Cost and Reserve [Line Items]
Costs incurred			$ 23		$ 89
Global Information Technology, HR Functions and Future Rent
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 12		23
Jardine Lloyd Thompson Group plc
Restructuring Cost and Reserve [Line Items]
Costs incurred			42		$ 251
Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, cost incurred to date	628		628
Costs incurred	19	$ 57	42	$ 137
Jardine Lloyd Thompson Group plc | Acquisition related | Corporate
Restructuring Cost and Reserve [Line Items]
Costs incurred	2		3
Jardine Lloyd Thompson Group plc | Acquisition related | Risk and Insurance Services Segment
Restructuring Cost and Reserve [Line Items]
Costs incurred	11		27
Jardine Lloyd Thompson Group plc | Acquisition related | Consulting Segment
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 6		$ 12

Restructuring Costs (Restructur

Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 81	$ 102
Amounts Accrued	23	89
Cash Paid	(47)	(100)
Non-Cash/Other	(2)	(10)
Liability at end of period	55	81
Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	36	51
Amounts Accrued	9	39
Cash Paid	(28)	(54)
Non-Cash/Other	0	0
Liability at end of period	17	36
Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	45	51
Amounts Accrued	14	50
Cash Paid	(19)	(46)
Non-Cash/Other	(2)	(10)
Liability at end of period	38	45
Jardine Lloyd Thompson Group plc
Restructuring Reserve [Roll Forward]
Liability at beginning of period	25	47
Amounts Accrued	42	251
Cash Paid	(44)	(226)
Non-cash charges	(8)	(47)
Liability at end of period	15	25
Jardine Lloyd Thompson Group plc | Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	16	42
Amounts Accrued	4	43
Cash Paid	(9)	(69)
Non-cash charges	0	0
Liability at end of period	11	16
Jardine Lloyd Thompson Group plc | Real estate related costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	7	5
Amounts Accrued	12	69
Cash Paid	(7)	(25)
Non-cash charges	(8)	(42)
Liability at end of period	4	7
Jardine Lloyd Thompson Group plc | Information Technology
Restructuring Reserve [Roll Forward]
Liability at beginning of period	2	0
Amounts Accrued	11	62
Cash Paid	(13)	(55)
Non-cash charges	0	(5)
Liability at end of period	0	2
Jardine Lloyd Thompson Group plc | Consulting and other outside services
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0	0
Amounts Accrued	15	77
Cash Paid	(15)	(77)
Non-cash charges	0	0
Liability at end of period	$ 0	$ 0

Common Stock (Details)

Common Stock (Details) - USD ($)	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Nov. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)		0
Purchase of treasury shares	$ 445,000,000
Payments for repurchase of common stock	$ 434,000,000	$ 0
Stock-based compensation, shares issued during period (in shares)	2,600,000	2,800,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Share repurchases program, authorized amount (up to)			$ 2,500,000,000
Common stock repurchased (in shares)	3,400,000
Stock repurchase program, remaining authorized repurchase amount	$ 2,000,000,000

Claims, Lawsuits And Other Co_2

Claims, Lawsuits And Other Contingencies (Details) - Jardine Lloyd Thompson Group plc case in Thousands, £ in Millions, $ in Millions	48 Months Ended
	Dec. 31, 2018case	Jun. 30, 2021GBP (£)	Jun. 30, 2021USD ($)	Dec. 31, 2020GBP (£)	Dec. 31, 2020USD ($)	Feb. 28, 2019GBP (£)	Feb. 28, 2019USD ($)
Loss Contingencies [Line Items]
Individual cases analyzed	14
Loss contingency accrual		£ 99	$ 137	£ 155	$ 210	£ 59	$ 77

Segment Information (Selected I

Segment Information (Selected Information And Details For MMC's Operating Segments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 5,017	$ 4,189	$ 10,100	$ 8,840
Operating Income (Loss)	1,228	885	2,586	1,955
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	3,141	2,603	6,366	5,514
Interest on fiduciary funds	3	9	8	32
Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,892	1,616	3,765	3,378
Operating Segments
Segment Reporting Information [Line Items]
Revenue	5,033	4,219	10,131	8,892
Operating Income (Loss)	1,294	951	2,715	2,087
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	3,141	2,603	6,366	5,514
Operating Income (Loss)	950	696	2,010	1,550
Interest on fiduciary funds	3	9	8	32
Equity method income (loss)	14	14	17	13
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,892	1,616	3,765	3,378
Operating Income (Loss)	344	255	705	537
Equity method income (loss)			0	4
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	(16)	(30)	(31)	(52)
Operating Income (Loss)	(66)	(66)	(129)	(132)
Intersegment Eliminations | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	4	4	4	5
Intersegment Eliminations | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	$ 12	$ 26	$ 27	$ 47

Segment Information (Details of

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting Information [Line Items]
Revenue	$ 5,017	$ 4,189	$ 10,100	$ 8,840
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	3,141	2,603	6,366	5,514
Risk and Insurance Services Segment | Marsh Insurance Group
Segment Reporting Information [Line Items]
Revenue	2,650	2,161	4,975	4,222
Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group
Segment Reporting Information [Line Items]
Revenue	488	433	1,383	1,260
Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,892	1,616	3,765	3,378
Consulting Segment | Mercer Consulting Group
Segment Reporting Information [Line Items]
Revenue	1,274	1,149	2,562	2,400
Consulting Segment | Oliver Wyman Group Consulting Group
Segment Reporting Information [Line Items]
Revenue	618	467	1,203	978
Operating Segments
Segment Reporting Information [Line Items]
Revenue	5,033	4,219	10,131	8,892
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	3,141	2,603	6,366	5,514
Operating Segments | Risk and Insurance Services Segment | Marsh Insurance Group
Segment Reporting Information [Line Items]
Revenue	2,652	2,168	4,981	4,244
Operating Segments | Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group
Segment Reporting Information [Line Items]
Revenue	489	435	1,385	1,270
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,892	1,616	3,765	3,378
Operating Segments | Consulting Segment | Mercer Consulting Group
Segment Reporting Information [Line Items]
Revenue	1,274	1,149	2,562	2,400
Operating Segments | Consulting Segment | Oliver Wyman Group Consulting Group
Segment Reporting Information [Line Items]
Revenue	618	467	1,203	978
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (16)	$ (30)	$ (31)	$ (52)