Marsh & McLennan Companies (MMC) 10-Q 31 Jul 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 24, 2020
Entity Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2020
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		506,529,315
Entity Central Index Key	0000062709
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 4,189	$ 4,349	$ 8,840	$ 8,420
Expense:
Compensation and benefits	2,429	2,537	4,984	4,819
Other operating expenses	875	1,132	1,901	1,983
Operating expenses	3,304	3,669	6,885	6,802
Operating income	885	680	1,955	1,618
Other net benefit credits	63	70	127	134
Interest income	2	2	4	30
Interest expense	(132)	(141)	(259)	(261)
Cost of extinguishment of debt	0	(32)	0	(32)
Investment (loss) income	(31)	8	(33)	13
Acquisition related derivative contracts	0	(37)	0	(8)
Income before income taxes	787	550	1,794	1,494
Income tax expense	207	206	447	423
Net income before non-controlling interests	580	344	1,347	1,071
Less: Net income attributable to non-controlling interests	8	12	21	23
Net income attributable to the Company	$ 572	$ 332	$ 1,326	$ 1,048
Net income per share attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 1.13	$ 0.66	$ 2.62	$ 2.07
Diluted net income per share attributable to the Company (usd per share)	$ 1.12	$ 0.65	$ 2.60	$ 2.05
Average number of shares outstanding:
Average number of shares outstanding - Basic (in shares)	506	507	505	506
Average number of shares outstanding - Diluted (in shares)	511	512	510	511
Shares outstanding (in shares)	506	507	506	507

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Statement of Comprehensive Income [Abstract]
Net income before non-controlling interests	$ 580	$ 344	$ 1,347	$ 1,071
Other comprehensive income (loss), before tax:
Foreign currency translation adjustments	241	13	(700)	109
Gain related to pension/post-retirement plans	34	63	209	20
Other comprehensive income (loss), before tax	275	76	(491)	129
Income tax expense on other comprehensive income	10	13	36	9
Other comprehensive income (loss), net of tax	265	63	(527)	120
Comprehensive income	845	407	820	1,191
Less: comprehensive income attributable to non-controlling interest	8	12	21	23
Comprehensive income attributable to the Company	$ 837	$ 395	$ 799	$ 1,168

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 1,711	$ 1,155
Receivables
Commissions and fees	5,045	4,608
Advanced premiums and claims	111	123
Other	635	645
Gross receivables	5,791	5,376
Less-allowance for credit losses	(144)	(140)
Net receivables	5,647	5,236
Other current assets	739	677
Total current assets	8,097	7,068
Goodwill	14,797	14,671
Other intangible assets	2,761	2,774
Fixed assets (net of accumulated depreciation and amortization of $2,052 at June 30, 2020 and $2,001 at December 31, 2019)	866	858
Pension related assets	1,672	1,632
Right of use assets	1,882	1,921
Deferred tax assets	618	676
Other assets	1,476	1,757
Total assets	32,169	31,357
Current liabilities:
Short-term debt	1,216	1,215
Accounts payable and accrued liabilities	2,668	2,746
Accrued compensation and employee benefits	1,345	2,197
Current lease liabilities	332	342
Accrued income taxes	367	179
Total current liabilities	5,928	6,679
Fiduciary liabilities	7,441	7,344
Less – cash and investments held in a fiduciary capacity	(7,441)	(7,344)
Net fiduciary assets	0	0
Long-term debt	11,985	10,741
Pension, post-retirement and post-employment benefits	2,197	2,336
Long-term lease liabilities	1,902	1,926
Liabilities for errors and omissions	350	335
Other liabilities	1,415	1,397
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, 2020 and December 31, 2019	561	561
Additional paid-in capital	814	862
Retained earnings	16,060	15,199
Accumulated other comprehensive loss	(5,582)	(5,055)
Non-controlling interests	166	150
Stockholders' equity before treasury stock	12,019	11,717
Less – treasury shares, at cost, 54,263,059 shares at June 30, 2020 and 57,013,097 shares at December 31, 2019	(3,627)	(3,774)
Total equity	8,392	7,943
Total liabilities and stockholders' equity	$ 32,169	$ 31,357

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Fixed assets, accumulated depreciation and amortization	$ 2,052	$ 2,001
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	54,263,059	57,013,097

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		9 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Operating cash flows:
Net income before non-controlling interests	$ 580	$ 344	$ 1,347	$ 1,071
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization of fixed assets and capitalized software			188	159
Amortization of intangible assets			174	151
Non cash lease expense			165	151
Adjustments and payments related to contingent consideration liability			(30)	(9)
Charge for early extinguishment of debt	0	32	0	32
Provision for deferred income taxes			7	82
Loss (gain) on investments	31	(8)	33	(13)
Net loss on disposition of assets			5	21
Share-based compensation expense			147	117
Change in fair value of acquisition-related derivative contracts			0	8
Changes in assets and liabilities:
Net receivables			(389)	(437)
Other current assets			(81)	(4)
Other assets			140	(33)
Accounts payable and accrued liabilities			(129)	29
Accrued compensation and employee benefits			(848)	(670)
Accrued income taxes			204	6
Contributions to pension and other benefit plans in excess of current year credit			(165)	(172)
Other liabilities			(20)	36
Operating lease liabilities			(164)	(155)
Effect of exchange rate changes			(6)	(129)
Net cash provided by operations			578	241
Financing cash flows:
Purchase of treasury shares			0	(100)
Net increase in commercial paper			0	549
Net borrowings from term-loan and credit facilities			1,000	300
Proceeds from issuance of debt			737	6,459
Repayments of debt			(507)	(457)
Payments for early extinguishment of debt			0	(585)
Purchase of non-controlling interests			(3)	(50)
Acquisition-related derivative payments			0	(337)
Shares withheld for taxes on vested units – treasury shares			(115)	(87)
Issuance of common stock from treasury shares			66	108
Payments of deferred and contingent consideration for acquisitions			(69)	(39)
Distributions of non-controlling interests			(22)	(15)
Dividends paid			(466)	(422)
Net cash provided by financing activities			621	5,324
Investing cash flows:
Capital expenditures			(200)	(161)
Net sales of long-term investments			103	202
Purchase of equity investment			0	(91)	$ (79)
Proceeds from sales of fixed assets			1	2
Dispositions			93	165
Acquisitions			(562)	(5,500)
Other, net			1	(47)
Net cash used for investing activities			(564)	(5,430)
Effect of exchange rate changes on cash and cash equivalents			(79)	93
Increase in cash and cash equivalents			556	228
Cash and cash equivalents at beginning of period			1,155	1,066
Cash and cash equivalents at end of period	$ 1,711	$ 1,294	$ 1,711	$ 1,294	$ 1,155

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	TREASURY SHARES	NON-CONTROLLING INTERESTS
Balance, beginning of period at Dec. 31, 2018		$ 561	$ 817	$ 14,347	$ (4,647)	$ (3,567)	$ 73
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(42)
Issuance of shares under stock compensation plans and employee stock purchase plans			(39)			221
Other			0
Net income attributable to the Company	$ 1,071			1,048			23
Dividend equivalents declared				(4)
Dividends declared				(650)
Other comprehensive loss, net of tax	120				120
Purchase of treasury shares						(100)
Net non-controlling interests acquired / (disposed)							195
Distributions and other changes							(19)
Balance, end of period at Jun. 30, 2019	$ 8,337	561	736	14,741	(4,527)	(3,446)	272
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 1.285
Balance, beginning of period at Mar. 31, 2019		561	681	14,642	(4,590)	(3,385)	77
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			59
Issuance of shares under stock compensation plans and employee stock purchase plans			(4)			39
Other			0
Net income attributable to the Company	$ 344			332			12
Dividend equivalents declared				(2)
Dividends declared				(231)
Other comprehensive loss, net of tax	63				63
Purchase of treasury shares						(100)
Net non-controlling interests acquired / (disposed)							195
Distributions and other changes							(12)
Balance, end of period at Jun. 30, 2019	$ 8,337	561	736	14,741	(4,527)	(3,446)	272
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0.455
Balance, beginning of period at Dec. 31, 2019	$ 7,943	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 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 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

Consolidated Statements of Eq_2

Consolidated Statements of Equity (Unaudited) (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Balance, end of period	$ 8,392		$ 7,943	$ 8,337
COMMON STOCK
Balance, end of period	$ 561	$ 561	$ 561	$ 561	$ 561	$ 561

Nature of Operations

Nature of Operations	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations Marsh & McLennan Companies, Inc. and its consolidated subsidiaries (the "Company") is a global professional services firm offering clients advice and solutions in risk, strategy and people. Its businesses include: Marsh, the insurance broker, intermediary and risk advisor; Guy Carpenter, the risk and reinsurance specialist; Mercer, the provider of HR and Investment related financial advice and services; and Oliver Wyman Group, the management, economic and brand consultancy. With 76,000 colleagues worldwide and annual revenue of $17 billion , the Company provides analysis, advice and transactional capabilities to clients in more than 130 countries. Business Update Related To COVID-19 In March 2020, the World Health Organization declared the Coronavirus (COVID-19) a pandemic. The outbreak spread quickly around the world, including essentially every geography in which the Company operates. The pandemic has created uncertainty around the impact on the global economy and has resulted in impacts to the financial markets and asset values. Governments implemented various restrictions around the world, including closure of non-essential businesses, travel, shelter-in-place requirements for citizens and other restrictions. The Company took a number of precautionary steps to safeguard its businesses and colleagues from COVID-19, including implementing travel restrictions, arranging work from home capabilities and flexible work policies. Through the end of the second quarter, nearly all of the Company’s colleagues have continued working fully in a remote work environment, with virtually no disruption to the Company as a whole and its ability to serve clients. The safety and well-being of our colleagues continues to be our first priority. Over the past several months, many countries have begun to “re-open” their economies, with various conditions imposed by each jurisdiction. The Company has re-opened offices in various locations around the world, while ensuring that it continues to adhere to guidelines and orders issued by national, state and local governments. The timing of office re-openings will vary based on the conditions and restrictions in each location, but it remains uncertain the extent to which colleagues will return to offices for the remainder of the year. However, the Company expects it will continue its ability to service clients effectively while colleagues remain in a remote work environment. The ultimate extent of the COVID-19 impact to the Company will depend on numerous evolving factors and future developments that it is not able to predict. Factors that could adversely affect the Company’s financial statements related to the financial and operational impact of COVID-19 are outlined in “Item 1A - Risk Factors” in the Company’s Form 10-Q for the quarter ended March 31, 2020. JLT Acquisition On April 1, 2019, the Company completed its acquisition (the "Transaction") of all of the outstanding shares of Jardine Lloyd Thompson Group plc ("JLT"), a public company organized under the laws of England and Wales. JLT's results of operations for the three and six month periods ended June 30, 2020 are included in the Company's results of operations. The Company's results for the six months ended June 30, 2019 do not reflect JLT’s results of operations for the three months ended March 31, 2019 and therefore may affect comparability.

Principles of Consolidation and

Principles of Consolidation and Other Matters	6 Months Ended
	Jun. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Principles of Consolidation and Other Matters	Principles of Consolidation and Other Matters The consolidated financial statements included herein have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission. While certain information and footnote 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 for interim filings, 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, 2019 (the " 2019 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 three and six month periods ended June 30, 2020 and 2019 . 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. Management has made estimates of the impact of COVID-19 within the Company’s financial statements and there may be changes to those estimates in future periods. In most situations where estimates, fair values or recoverability of assets is dependent upon short or long term projections of cash flows, revenues or earnings before interest, taxes, depreciation and amortization ("EBITDA"), the Company has based its projections assuming the gradual lifting of global lockdowns starting in the third quarter, but recessionary conditions persisting through at least the remainder of 2020. The Company has also considered potential impacts to its customer base in various industries and geographies. The ultimate extent to which the COVID-19 pandemic will directly or indirectly impact the Company’s businesses, results of operations and financial condition will depend on future developments that are highly uncertain, including new information that may emerge concerning COVID-19 and the actions taken to contain it or treat it, and the economic impact on local, regional, national and international customers and markets. 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, 2020 , the Company maintained $201 million compared to $197 million at December 31, 2019 related to these regulatory requirements. Allowance for Current Expected Credit Losses on Accounts Receivable The Company’s policy for providing an allowance for current expected credit losses (“CECL”) on its accounts receivable is based on management’s best estimate of amounts that will be uncollectible primarily based on the Company’s historical experience of collections in its various businesses and other events that may affect the net realizable value of receivables. The charge related to expected credit losses was immaterial to the consolidated statement of income in the three and six month periods ended June 30, 2020. Investments The caption "Investment (loss) income" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds. The Company holds investments in certain private equity funds that are accounted for under 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 losses of $31 million and $33 million for the three and six month periods ended June 30, 2020 compared to net investment income of $8 million and $13 million for the three and six month periods ended June 30, 2019 . The three and six month periods ending June 30, 2020 primarily include a loss of $23 million from the sale of shares of Alexander Forbes and losses related to its private equity fund investments. The three and six month periods ending June 30, 2019 include gains of $3 million and $6 million related to mark-to-market changes in equity securities and gains of $5 million and $7 million related to investments in private equity funds and other investments. Income Taxes The Company's effective tax rate in the second quarter of 2020 was 26.2% compared with 37.4% in the second quarter of 2019 . The effective tax rates for the first six months of 2020 and 2019 were 24.9% and 28.2% . The rate in the second quarter and first six months of 2019 reflects discrete adjustments related to the JLT acquisition, including tax on the disposition of JLT’s aerospace business and nondeductible expenses incurred in connection with the JLT Transaction. The tax rates in all periods reflect the impact of discrete tax matters such as excess tax benefits related to share-based compensation, 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 decreased from $86 million at December 31, 2019 to $79 million at June 30, 2020 due to settlements of audits, expirations of statutes of limitation and net changes to tax positions of prior years, offset by current accruals. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $12 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 reliant on estimates of future sub-lease income to be received and future contractual costs to be incurred. These costs are included in other operating expenses in the consolidated statements of income. Other costs related to 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, 2020
Revenue from Contract with Customer [Abstract]
Revenue	Revenue The core principle of the revenue recognition guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve that principle, the entity applies the following steps: identify the contract(s) with the customer, identify the performance obligations in the contract(s), determine the transaction price, allocate the transaction price to the performance obligations in the contract and recognize revenue when (or as) the entity satisfies a performance obligation. Under the accounting guidance, a performance obligation is satisfied either at a “point in time” or “over time” depending on the nature of the product or service provided, and the specific terms of the contract with customers. The Company's revenue recognition guidance is provided in more detail in Note 3 of the consolidated financial statements and the notes thereto included in 2019 Form 10-K for the year ended December 31, 2019 . The following schedule disaggregates components of the Company's revenue: Three Months Ended Six Months Ended (In millions) 2020 2019 2020 2019 Marsh: EMEA $ 597 $ 652 $ 1,351 $ 1,285 Asia Pacific 298 291 536 456 Latin America 99 116 190 194 Total International 994 1,059 2,077 1,935 U.S./Canada 1,167 1,097 2,145 1,958 Total Marsh 2,161 2,156 4,222 3,893 Guy Carpenter 433 392 1,260 1,055 Subtotal 2,594 2,548 5,482 4,948 Fiduciary interest income 9 26 32 49 Total Risk and Insurance Services $ 2,603 $ 2,574 $ 5,514 $ 4,997 Mercer: Wealth $ 561 $ 613 $ 1,153 $ 1,156 Health 432 458 918 900 Career 156 189 329 359 Total Mercer 1,149 1,260 2,400 2,415 Oliver Wyman 467 540 978 1,058 Total Consulting $ 1,616 $ 1,800 $ 3,378 $ 3,473 The Company recognizes commission revenue from arrangements for a significant portion of its brokerage arrangements at a point in time at 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, 2020 December 31, 2019 Contract Assets $ 298 $ 207 Contract Liabilities $ 696 $ 593 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 sheet. Contract liabilities primarily relate to the advance consideration received from customers. Contract liabilities are included in current liabilities in the Company's consolidated balance sheet. Revenue recognized in the first six months of 2020 and 2019 that was included in the contract liability balance at the beginning of each of those years was $418 million and $307 million , respectively. The amount of revenue recognized in the first six months of 2020 and 2019 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 $67 million and $36 million , respectively. 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 described above 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. Approximately $33 million of the revenue reduction is related to Marsh in the U.S. and EMEA geographies. Mercer’s revenue was reduced by approximately $3 million in the Health segment. The Company applies the practical expedient and therefore does not disclose the value of unsatisfied performance obligations for (1) contracts with original contract terms of one year or less and (2) contracts where the Company has the right to invoice for services performed. The revenue expected to be recognized in future periods during the non-cancellable term of existing contracts greater than one year that is related to performance obligations that are unsatisfied or partially satisfied at the end of the reporting period is approximately $51 million for Marsh, $220 million for Mercer and $2 million for Oliver Wyman. The Company expects revenue in 2021, 2022, 2023, 2024 and 2025 and beyond of $146 million , $71 million , $36 million , $14 million and $6 million , respectively, related to these performance obligations.

Fiduciary Assets and Liabilitie

Fiduciary Assets and Liabilities	6 Months Ended
	Jun. 30, 2020
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. Unremitted 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 $9 million and $32 million for the three and six month periods ended June 30, 2020 , respectively, and $26 million and $49 million for the three and six month periods ended June 30, 2019 , respectively. The Consulting segment recorded fiduciary interest income of less than $1 million for both the three and six month periods ended June 30, 2020 , and $1 million and $2 million for the three and six month periods ended June 30, 2019, respectively. 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 $11.6 billion at June 30, 2020 and $8.9 billion at December 31, 2019 . 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, 2020
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) 2020 2019 2020 2019 Net income before non-controlling interests $ 580 $ 344 $ 1,347 $ 1,071 Less: Net income attributable to non-controlling interests 8 12 21 23 Net income attributable to the Company $ 572 $ 332 $ 1,326 $ 1,048 Basic weighted average common shares outstanding 506 507 505 506 Dilutive effect of potentially issuable common shares 5 5 5 5 Diluted weighted average common shares outstanding 511 512 510 511 Average stock price used to calculate common stock equivalents $ 101.17 $ 95.74 $ 104.14 $ 92.14

Supplemental Disclosures to the

Supplemental Disclosures to the Consolidated Statements of Cash Flows	6 Months Ended
	Jun. 30, 2020
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, 2020 and 2019 . (In millions) 2020 2019 Assets acquired, excluding cash $ 752 $ 8,593 Liabilities assumed (29 ) (2,718 ) Non-controlling interests assumed — (309 ) Contingent/deferred purchase consideration (161 ) (66 ) Net cash outflow for current year acquisitions $ 562 $ 5,500 (In millions) 2020 2019 Interest paid $ 248 $ 141 Income taxes paid, net of refunds $ 227 $ 327 The classification of contingent consideration in the statement of cash flows is determined by 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 $69 million for the six months ended June 30, 2020 . This consisted of deferred purchase consideration related to prior years' acquisitions of $27 million and contingent consideration of $42 million . For the six months ended June 30, 2019 , the Company paid deferred and contingent consideration of $39 million , consisting of deferred purchase consideration related to prior years' acquisitions of $23 million and contingent consideration of $16 million . The following amounts are included in the operating section of the consolidated statements of cash flows. 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 . For the six months ended June 30, 2019 , the Company recorded an expense for adjustments to contingent consideration liabilities of $20 million and made contingent consideration payments of $29 million . The Company had non-cash issuances of common stock under its share-based payment plan of $213 million and $162 million for the six months ended June 30, 2020 and 2019 , respectively. The Company recorded stock-based compensation expense for equity awards related to restricted stock units, performance stock units and stock options of $147 million and $117 million for the six -month periods ended June 30, 2020 and 2019 , respectively.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2020
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, 2020 and 2019 , 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, 2020 $ (3,374 ) $ (2,473 ) $ (5,847 ) Other comprehensive 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 April 1, 2019 $ (2,990 ) $ (1,600 ) $ (4,590 ) Other comprehensive income before reclassifications 29 15 44 Amounts reclassified from accumulated other comprehensive income 19 — 19 Net current period other comprehensive income 48 15 63 Balance as of June 30, 2019 $ (2,942 ) $ (1,585 ) $ (4,527 ) (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 (loss) income 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 ) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2018 $ (2,953 ) $ (1,694 ) $ (4,647 ) Other comprehensive income (loss) before reclassifications (30 ) 109 79 Amounts reclassified from accumulated other comprehensive income 41 — 41 Net current period other comprehensive income 11 109 120 Balance as of June 30, 2019 $ (2,942 ) $ (1,585 ) $ (4,527 ) The components of other comprehensive income (loss) for the three and six -month periods ended June 30, 2020 and 2019 are as follows: Three Months Ended June 30, 2020 2019 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 241 $ 4 $ 237 $ 13 $ (2 ) $ 15 Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (1 ) — (1 ) — — — Net actuarial losses (a) 40 8 32 26 6 20 Effect of remeasurement (a) — — — (1 ) — (1 ) Subtotal 39 8 31 25 6 19 Foreign currency translation adjustments (5 ) (2 ) (3 ) 38 9 29 Pension/post-retirement plans gains 34 6 28 63 15 48 Other comprehensive income $ 275 $ 10 $ 265 $ 76 $ 13 $ 63 (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, 2020 2019 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (700 ) $ (7 ) $ (693 ) $ 109 $ — $ 109 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) 80 19 61 52 12 40 Effect of remeasurement (a) — — — (1 ) — (1 ) Effect of settlement (a) — — — 4 1 3 Subtotal 79 19 60 54 13 41 Foreign currency translation adjustments 130 24 106 (34 ) (4 ) (30 ) Pension/post-retirement plans gains 209 43 166 20 9 11 Other comprehensive (loss) income $ (491 ) $ 36 $ (527 ) $ 129 $ 9 $ 120 (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, 2020
Business Combinations [Abstract]
Acquisitions and Dispositions	Acquisitions and Dispositions The Company’s acquisitions have been accounted for as business combinations. Net assets and results of operations are included in the Company’s consolidated financial statements commencing at the respective purchase closing dates. In connection with acquisitions, the Company records the estimated values of the net tangible assets and the identifiable intangible assets purchased, which typically consist of customer relationships, developed technology, trademarks and non-compete agreements. The valuation of purchased intangible assets involves significant estimates and assumptions. 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 four acquisitions during the first six months of 2020. • January – Marsh & McLennan Agency ("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 independent brokerage agency 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. Total purchase consideration for acquisitions made during the six months ended June 30, 2020 was $737 million , which consisted of cash paid of $576 million and deferred purchase consideration 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 to four years. The Company also paid $27 million of deferred purchase consideration and $78 million of contingent consideration related to acquisitions made in prior years. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment until purchase accounting is finalized. The following table presents the preliminary allocation of purchase consideration to the assets acquired and liabilities assumed during 2020 based on the estimated fair values for the acquisitions as of their respective acquisition dates: Acquisitions through June 30, 2020 (In millions) Cash 576 Estimated fair value of deferred/contingent consideration 161 Total consideration $ 737 Allocation of purchase price: Cash and cash equivalents 14 Accounts receivable, net 28 Fixed assets, net 16 Other intangible assets 277 Goodwill 466 Deferred tax assets (43 ) Other assets 8 Total assets acquired 766 Current liabilities 19 Other liabilities 10 Total liabilities assumed 29 Net assets acquired $ 737 The purchase price allocation above 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 2020 : Intangible assets through June 30, 2020 (In millions) Amount Weighted Average Amortization Period Client relationships $ 255 13.3 years Other 22 4.5 years $ 277 Dispositions During 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 . At December 31, 2019, the Company owned approximately 443 million shares of the common stock of Alexander Forbes ("AF"), a South African company listed on the Johannesburg Stock Exchange, which was accounted for under the equity method of accounting. In February 2020, the Company sold approximately 49 million shares of the common stock of AF, and in May 2020, sold an additional 193 million shares to third parties, leaving the Company with an investment of approximately 201 million shares of the common stock of AF at June 30, 2020. Upon completion of the May transaction, the investment in AF is accounted at fair value, with investment gains and losses recorded as investment income in the consolidated statement of income. Prior-Year Acquisitions On April 1, 2019, the Company completed the JLT Transaction and purchased all of the outstanding shares of JLT. Under the terms of the Transaction, JLT shareholders received £19.15 in cash for each JLT share, which valued JLT’s existing issued and to be issued share capital at approximately £4.3 billion (or approximately $5.6 billion based on an exchange rate of U.S. $1.31 : £1 ). The Company also assumed existing JLT long-term indebtedness of approximately $1 billion . The Company implemented the Transaction by way of a scheme of arrangement under Part 26 of the United Kingdom Companies Act 2006, as amended. The Risk and Insurance Services segment completed five other acquisitions during 2019 . • February – MMA acquired Bouchard Insurance, Inc., a Florida-based full service agency and Employee Benefits Group, Inc., a Maryland-based independent insurance agency. • April – MMA acquired Lovitt & Touche, Inc., an Arizona-based insurance agency and The Centurion Group, LLC, a Pennsylvania-based retirement consulting, asset management and benefit plan advisory firm. • October – MMA acquired Benefits Reports Insurance Services, Inc., a Massachusetts-based independent insurance agency. Total purchase consideration for acquisitions made during the first six months of 2019 was $5,925 million , which consisted of cash paid of $5,859 million and deferred purchase consideration and estimated contingent consideration of $66 million . Contingent consideration arrangements are primarily based on EBITDA or revenue targets over a period of two to four years. The fair value of the contingent consideration was based on projected revenue or EBITDA of the acquired entities. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment when purchase accounting is finalized. For the first six months of 2019, the Company also paid $23 million of deferred purchase consideration and $45 million of contingent consideration related to acquisitions made in prior years. Subsequent to the JLT acquisition, the Company purchased the outstanding non-controlling interests of several JLT subsidiaries for cash payments of approximately $79 million . In January 2019, Marsh increased its equity ownership in Marsh India from 26% to 49% . Marsh India is accounted for under the equity method. Prior year dispositions During the third quarter of 2019, the Company completed the sale of a U.S. Specialty business at Marsh and a U.S. large market health and defined benefit business at Mercer for cash proceeds of approximately $60 million . Also, on June 1, 2019, the Company completed its disposition of JLT’s global aerospace business for cash proceeds of $165 million and contingent consideration receivable of approximately $65 million , based on the aerospace business achieving certain revenue milestones in 2020. The aerospace business was divested as part of the European Commission's approval of the JLT Transaction. Pro-Forma Information The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during 2020 and 2019. In accordance with accounting guidance related to pro-forma disclosures, the information presented for current year acquisitions is as if they occurred on January 1, 2019 and reflects acquisitions made in 2019 as if they occurred on January 1, 2018. The unaudited pro-forma information adjusts for the effects of amortization of acquired intangibles and additional interest expense related to the issuance of debt related to the JLT Transaction. 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) 2020 2019 2020 2019 Revenue $ 4,189 $ 4,395 $ 8,891 $ 8,963 Net income attributable to the Company $ 574 $ 488 $ 1,328 $ 1,146 Basic net income per share attributable to the Company $ 1.13 $ 0.96 $ 2.63 $ 2.26 Diluted net income per share attributable to the Company $ 1.12 $ 0.95 $ 2.60 $ 2.24 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 periods ended June 30, 2020 include approximately $48 million and $63 million of revenue, respectively, and operating income of $7 million and $11 million , respectively, for acquisitions made in 2020. The consolidated statements of income for the three and six month periods ended June 30, 2019 included approximately $486 million and $496 million , respectively, of revenue, and operating income of $16 million and $18 million , respectively, related to acquisitions made in 2019.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	6 Months Ended
	Jun. 30, 2020
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 goodwill impairment test. Alternatively, the company may elect to proceed directly to the quantitative goodwill impairment test. In 2019, the Company elected to perform a quantitative impairment assessment. Fair values of the reporting units were estimated using a market approach. Carrying values for the reporting units are based on balances at the prior quarter end and include directly identified assets and liabilities, as well as an allocation of those assets and liabilities not recorded at the reporting unit level. The Company completed its 2019 annual review in the third quarter and concluded goodwill was not impaired, as the fair value of each reporting unit exceeded its carrying value by a substantial margin. Other intangible assets that are not deemed to have an indefinite life are amortized over their estimated lives and reviewed for impairment upon the occurrence of certain triggering events in accordance with applicable accounting literature. The Company does not have any indefinite lived intangible assets. Changes in the carrying amount of goodwill are as follows: June 30, (In millions) 2020 2019 Balance as of January 1, $ 14,671 $ 9,599 Goodwill acquired 466 4,895 Other adjustments (a) (340 ) (15 ) Balance at June 30, $ 14,797 $ 14,479 (a) Primarily reflects the impact of foreign exchange. The entire amount of goodwill acquired of $466 million in 2020 is related to the Risk and Insurance Services segment, of which $141 million is deductible for tax purposes. The goodwill arising from the acquisitions consists largely of the synergies and economies of scale expected from combining the operations of the Company and the acquired entities and the trained and assembled workforce acquired. Goodwill allocable to the Company’s reportable segments at June 30, 2020 is as follows: Risk and Insurance Services, $11.2 billion and Consulting, $3.6 billion . The gross cost and accumulated amortization of identified intangible assets at June 30, 2020 and December 31, 2019 are as follows: June 30, 2020 December 31, 2019 (In millions) Gross Cost Accumulated Amortization Net Carrying Amount Gross Cost Accumulated Amortization Net Carrying Amount Client Relationships $ 3,592 $ 1,002 $ 2,590 $ 3,494 $ 897 $ 2,597 Other (a) 390 219 171 380 203 177 Amortized intangibles $ 3,982 $ 1,221 $ 2,761 $ 3,874 $ 1,100 $ 2,774 (a) Primarily non-compete agreements, trade names and developed technology. Aggregate amortization expense for the six months ended June 30, 2020 and 2019 was $174 million and $151 million , respectively. The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2020 (excludes amortization through June 30, 2020) $ 181 2021 347 2022 321 2023 296 2024 282 Subsequent years 1,334 $ 2,761 The developments in the COVID-19 pandemic have resulted in uncertainty in the global economy and declines in equity markets. The Company considered whether such events would indicate an interim goodwill assessment should be performed or that identified intangible assets and other long lived assets may not be recoverable. Based on its analysis, the Company concluded that the current events and circumstances related to the COVID-19 pandemic do not indicate that an impairment of goodwill is more likely than not or that identified intangibles are not recoverable.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
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 include treasury locks and 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 include assets and liabilities for contingent purchase consideration and the deal contingent foreign exchange contract (the "FX Contract") discussed in more detail in Note 11. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued 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 to four years. The fair value of the contingent purchase consideration asset and liability is estimated as the present value of future cash flows to be paid, based on projections of revenue and earnings and related targets of the acquired and disposed entities. Foreign Exchange Forward Contract Liabilities - Level 3 In connection with the JLT Transaction, the Company entered into the FX Contract, to hedge the risk of appreciation of the GBP-denominated purchase price. The Company settled the FX Contract on April 1, 2019, upon completion of the JLT Transaction. 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, 2020 and December 31, 2019 . Identical Assets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Total (In millions) 06/30/20 12/31/19 06/30/20 12/31/19 06/30/20 12/31/19 06/30/20 12/31/19 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 59 $ 4 $ — $ — $ — $ — $ 59 $ 4 Mutual funds (a) 155 166 — — — — 155 166 Money market funds (b) 530 55 — — — — 530 55 Other equity investment (a) — — 8 8 — — 8 8 Contingent purchase consideration asset (c) — — — — 64 84 64 84 Total assets measured at fair value $ 744 $ 225 $ 8 $ 8 $ 64 $ 84 $ 816 $ 317 Fiduciary Assets: U.S. Treasury Bills $ 55 $ 40 $ — $ — $ — $ — $ 55 $ 40 Money market funds 79 360 — — — — 79 360 Total fiduciary assets measured at fair value $ 134 $ 400 $ — $ — $ — $ — $ 134 $ 400 Liabilities: Contingent purchase consideration liability (d) $ — $ — $ — $ — $ 233 $ 225 $ 233 $ 225 Total liabilities measured at fair value $ — $ — $ — $ — $ 233 $ 225 $ 233 $ 225 (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 at June 30, 2020 and other assets at December 31, 2019 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 above chart reflect contingent purchase consideration from the sale of businesses during 2019, including accretion and adjustments to the fair value of the acquisition related asset of approximately $16 million through the second quarter of 2020. A 5% increase or decrease in the projections used to estimate the contingent consideration would result in a corresponding increase or decrease of the asset of approximately $6 million . During the six -month period ended June 30, 2020 , there were no assets or liabilities that were transferred between any of the levels. The table below 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, 2020 and 2019 : Three Months Ended Six Months Ended (In millions) 2020 2019 2020 2019 Balance at beginning of period $ 239 $ 454 $ 225 $ 508 Net Additions 66 29 96 40 Payments (65 ) (10 ) (78 ) (45 ) Revaluation Impact (11 ) 9 (10 ) 20 Change in fair value of the FX contract — (283 ) — (325 ) Other (a) 4 (3 ) — (2 ) Balance at June 30, $ 233 $ 196 $ 233 $ 196 (a) Primarily reflects the impact of foreign exchange. As set forth in the table above, based on the Company's ongoing assessment of the fair value of contingent consideration, the Company recorded a net decrease in the estimated fair value of such liabilities for prior-period acquisitions of $10 million in the six -month period ended June 30, 2020 . A 5% increase in the projections used to estimate the contingent consideration would increase the liability by approximately $14 million . A 5% decrease would decrease the liability by approximately $16 million . Long-Term Investments The Company holds investments in certain private equity investments, public companies and private companies that are accounted for using the equity method of accounting. The carrying value of these investments was $264 million and $434 million at June 30, 2020 and December 31, 2019 , respectively. Investments Accounted For Using the Equity Method of Accounting Investments in Public and Private Companies The Company has other investments in private insurance and consulting companies with a carrying value of $171 million and $183 million at June 30, 2020 and December 31, 2019 , respectively. The Company’s equity investments in insurance and consulting companies 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 $93 million and $107 million at June 30, 2020 and December 31, 2019 , 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 losses of $6 million and $7 million from these investments for the three and six month periods ended June 30, 2020 , respectively, compared to net investment gains of $5 million and $7 million for the same periods in 2019 . Other Investments At June 30, 2020 and December 31, 2019 , the Company held certain equity investments with readily determinable market values of $72 million and $19 million , respectively. The Company recorded investment losses on these investments of $2 million and $3 million in the three and six month periods ended June 30, 2020 , respectively, and investment gains of $3 million and $6 million for the same periods in 2019. The Company also held investments without readily determinable market values of $45 million and $67 million at June 30, 2020 and December 31, 2019 , respectively. At December 31, 2019, the Company owned approximately 443 million shares of the common stock of AF, a South African company listed on the Johannesburg Stock Exchange, which was accounted for under the equity method of accounting. In February 2020, the Company sold approximately 49 million shares of the common stock of AF, and in May 2020, sold an additional 193 million shares to third parties, leaving the Company with an investment of approximately 201 million shares of the common stock of AF at June 30, 2020. Upon completion of the May transaction, the investment in AF is accounted at fair value, with investment gains and losses recorded as investment income (loss) in the consolidated statement of income. The fair value of AF at June 30, 2020 was $55 million . In March 2019, the Company disposed of its investment in BenefitFocus for total proceeds of approximately $132 million . The Company received $115 million in the first quarter of 2019 and $17 million in April 2019. During the second quarter of 2019, the Company disposed of its investment in Payscale and received approximately $47 million

Derivatives

Derivatives	6 Months Ended
	Jun. 30, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivatives	Derivatives On September 20, 2018, the Company entered into the FX Contract to purchase £5.2 billion at a contracted exchange rate, to hedge the risk of appreciation of the GBP-denominated purchase price of JLT, which was settled on April 1, 2019, upon the closing of the JLT Transaction. The FX Contract did not qualify for hedge accounting treatment under applicable accounting guidance, which required the Company to record the change in the fair value of the FX Contract on each reporting date to the statement of income. A loss of $11 million was recorded in the second quarter of 2019, resulting in a net gain of $31 million for the six month period ended June 30, 2019 related to the settlement of the FX contract. In connection with the JLT Transaction, to hedge the economic risk of changes in future interest rates prior to its issuance of fixed rate debt, in the fourth quarter of 2018 the Company entered into treasury lock contracts related to $2 billion of senior notes issued in January 2019. The contracts were not designated as an accounting hedge. In January 2019, upon issuance of the $5 billion of senior notes, the Company settled the treasury lock derivatives and made a payment to its counter party for $122 million . A charge of $6 million was recorded in the first quarter of 2019 related to the settlement of the Treasury lock derivatives. In March 2019, the Company issued €1.1 billion of senior notes related to the JLT Transaction. See Note 14 for additional information related to the Euro senior note issuances. In connection with the senior note issuances, the Company entered into a forward exchange contract to hedge the economic risk of changes in foreign exchange rates from the issuance date to settlement date of the Euro senior notes. The Company recorded a charge of $7.3 million in the consolidated statement of income for the quarter ended March 31, 2019 upon settlement of this contract. JLT Derivatives and Hedging Activity A significant portion of JLT's outstanding senior notes at the time of completion of the JLT Transaction were denominated in U.S. dollars. In order to hedge its exposure against the risk of fluctuations between the British pound and the U.S. dollar, JLT entered into foreign exchange contracts as well as interest rate swaps to protect against the risk of changes in interest rates, which were designated as fair value hedges. In June, 2019, the Company redeemed these U.S. dollar denominated senior notes and settled the related derivative contracts. The offsetting changes in fair value of the debt and the change in fair value of the derivative contracts were recorded in the consolidated statement of income for the three months ended June 30, 2019. JLT also had a number of foreign exchange contracts to hedge the risk of foreign exchange movements between the U.S. dollar and the British pound, related to JLT’s U.S. dollar denominated revenue in the U.K. Prior to the acquisition, these derivative contracts were designated as cash flow hedges. Upon completion of the JLT Transaction, these derivative contracts were not re-designated as cash flow hedges by the Company. The contracts were settled in June 2019. The change in fair value between the acquisition date and the settlement date resulted in a charge of $26 million in the second quarter of 2019. The charge is recorded as a change in fair value of acquisition related derivative contracts in the consolidated statement of income. Net Investment Hedge The Company has investments in various subsidiaries with Euro functional currencies. As a result, the Company is exposed to the risk of fluctuations between the Euro and U.S. dollar exchange rates. The Company designated its €1.1 billion senior note debt instruments ("euro notes") as a net investment hedge (the "Hedge") of its Euro denominated subsidiaries. The Hedge effectiveness is re-assessed each quarter to confirm that the designated equity balance at the beginning of each period continues to equal or exceed 80% of the outstanding balance of the Euro debt instrument and that all the critical terms of the hedging instrument and the hedged net investment continue to match. If the Company concludes that the hedge is highly effective, the change in the debt balance related to foreign exchange fluctuations is recorded in foreign currency translation gains (losses) in the consolidated balance sheet. The Company concluded that the hedge continues to be highly effective as of June 30, 2020. During 2020, the U.S. dollar value of the euro notes increased $11 million through June 30 due to the impact of foreign exchange rates, with a corresponding decrease to foreign currency translation gains (losses).

Leases

Leases	6 Months Ended
	Jun. 30, 2020
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. For operating leases entered into prior to January 1, 2019, the Right-of-Use ("ROU") assets and operating lease liabilities are recognized in the balance sheet based on the present value of the remaining future minimum payments over the lease term from the implementation date of the standard, January 1, 2019. The ROU asset was adjusted for unamortized lease incentives and restructuring liabilities that were reported, prior to January 1, 2019, as other liabilities in the consolidated balance sheet. For leases entered into subsequent to January 1, 2019, the operating lease ROU asset and operating lease liabilities are based on the present value of 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. As a practical expedient, the Company has elected an accounting policy not to separate non-lease components from lease components and instead, accounts for these components as a single lease component. The Company has made an accounting policy election not to recognize ROU assets and lease liabilities for leases that, at the commencement date, are for 12 months or less. 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. The following chart provides additional information about the Company’s property leases: Three Months ended June 30, Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Lease Cost: Operating lease cost $ 97 $ 100 $ 189 $ 182 Short-term lease cost 1 2 2 3 Variable lease cost 27 39 64 76 Sublease income (5 ) (4 ) (10 ) (8 ) Net lease cost $ 120 $ 137 $ 245 $ 253 Other information: Operating cash outflows from operating leases $ 197 187 Right of use assets obtained in exchange for new operating lease liabilities $ 129 67 Weighted-average remaining lease term – real estate 8.53 years 8.99 years Weighted-average discount rate – real estate leases 3.05 % 3.08 % Future minimum lease payments for the Company’s operating leases as of June 30, 2020 are as follows: Payment Dates (In millions) Real Estate Leases Remainder of 2020 $ 208 2021 373 2022 348 2023 303 2024 259 2025 233 Subsequent years 822 Total future lease payments 2,546 Less: Imputed interest (312 ) Total $ 2,234 Current lease liabilities $ 332 Long-term lease liabilities 1,902 Total lease liabilities $ 2,234 Note: Table excludes obligations for leases with original terms of 12 months or less which have not been recognized as a right to use asset or liability in the consolidated balance sheets. As of June 30, 2020 , the Company had additional operating real estate leases that had not yet commenced of $17 million . These operating leases will commence over the next 12 months.

Retirement Benefits

Retirement Benefits	6 Months Ended
	Jun. 30, 2020
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. Plan was 64% equities and equity alternatives and 36% fixed income. At June 30, 2020 the actual allocation for the Company's U.S. Plan was 61% equities and equity alternatives and 39% fixed income. The target allocation for the U.K. Plans at June 30, 2020 was 33% equities and equity alternatives and 67% fixed income. At June 30, 2020 , the actual allocation for the U.K. Plans was 31% equities and equity alternatives and 69% fixed income. The Company's U.K. Plans comprised approximately 81% of non-U.S. plan assets at December 31, 2019 . 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. JLT Defined Benefit Pension Plans As part of the JLT Transaction, the Company has assumed responsibility for a number of pension plans throughout the world, with $255 million of net pension liabilities as of December 31, 2019 (approximately $1,003 million in liabilities and $748 million of plan assets), the most significant of which is the JLT U.K. Plan. The JLT U.K. Plan has a defined benefit section which was frozen to future accrual in 2006 and a defined contribution section. The assets of the scheme are held in a trustee administered fund separate from the Company. 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 Benefits Post-retirement Benefits For the Three Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 9 $ 10 $ — $ — Interest cost 104 121 — — Expected return on plan assets (207 ) (217 ) — — Recognized actuarial loss 40 26 — — Net periodic benefit credit $ (54 ) $ (60 ) $ — $ — Combined U.S. and significant non-U.S. Plans Pension Benefits Post-retirement Benefits For the Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 17 $ 18 $ — $ — Interest cost 210 240 1 1 Expected return on plan assets (417 ) (430 ) — — Amortization of prior service credit — — (1 ) (1 ) Recognized actuarial loss 80 52 — — Net periodic benefit credit $ (110 ) $ (120 ) $ — $ — Settlement loss — 4 — — Total credit $ (110 ) $ (116 ) $ — $ — 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) 2020 2019 2020 2019 Compensation and benefits expense (Operating income) $ 9 $ 10 $ — $ — Other net benefit credits (63 ) (70 ) — — Total (credit) cost $ (54 ) $ (60 ) $ — $ — 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) 2020 2019 2020 2019 Compensation and benefits expense (Operating income) $ 17 $ 18 $ — $ — Other net benefit credits (127 ) (134 ) — — Total credit $ (110 ) $ (116 ) $ — $ — U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2020 2019 2020 2019 Interest cost $ 54 $ 60 $ — $ — Expected return on plan assets (87 ) (85 ) — — Recognized actuarial loss 18 11 — — Net periodic benefit credit $ (15 ) $ (14 ) $ — $ — U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Interest cost $ 107 $ 120 $ — $ — Expected return on plan assets (173 ) (171 ) — — Recognized actuarial loss (credit) 36 22 — — Net periodic benefit credit $ (30 ) $ (29 ) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 9 $ 10 $ — $ — Interest cost 50 61 — — Expected return on plan assets (120 ) (132 ) — — Recognized actuarial loss 22 15 — — Net periodic benefit credit $ (39 ) $ (46 ) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 17 $ 18 $ — $ — Interest cost 103 120 1 1 Expected return on plan assets (244 ) (259 ) — — Amortization of prior service credit — — (1 ) (1 ) Recognized actuarial loss 44 30 — — Net periodic benefit credit $ (80 ) $ (91 ) $ — $ — Settlement loss — 4 — — Total credit $ (80 ) $ (87 ) $ — $ — 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, 2020 2019 2020 2019 Weighted average assumptions: Expected return on plan assets 5.31 % 5.74 % — — Discount rate 2.57 % 3.48 % 2.72 % 3.65 % Rate of compensation increase 1.76 % 1.74 % — — The Company made approximately $53 million of contributions to its U.S. and non-U.S. defined benefit pension plans for the six months ended June 30, 2020 . After consideration of the deferral discussed below, the Company expects to contribute approximately $57 million to its U.S. and non-U.S. defined benefit pension plans during the remainder of 2020 . Pursuant to the terms of the Coronavirus Aid, Relief and Economic Security Act (the “CARES Act”), contributions previously due during 2020 will be deferred until January 1, 2021. As a result, the Company will defer funding of approximately $47 million to its U.S. qualified defined benefit plans until January 1, 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 $73 million and $70 million for the six months ended June 30, 2020 and 2019 , respectively. The cost of the U.K. DC Plans was $64 million and $46 million for the six months ended June 30, 2020 and 2019 , respectively.

Debt

Debt	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Debt	Debt The Company’s outstanding debt is as follows: (In millions) June 30, December 31, Short-term: Term loan facility - one year 500 — Current portion of long-term debt 716 1,215 1,216 1,215 Long-term: Senior notes – 2.35% due 2020 — 500 Senior notes – 3.50% due 2020 699 698 Senior notes – 4.80% due 2021 499 499 Senior notes - Floating rate due 2021 299 298 Senior notes – 2.75% due 2022 499 498 Senior notes – 3.30% due 2023 349 349 Senior notes – 4.05% due 2023 249 249 Senior notes – 3.50% due 2024 598 597 Senior notes – 3.875% due 2024 994 994 Senior notes – 3.50% due 2025 497 497 Senior notes – 1.349% due 2026 615 609 Senior notes – 3.75% due 2026 597 597 Senior notes – 4.375% due 2029 1,499 1,499 Senior notes – 1.979% due 2030 612 607 Senior notes – 2.250% due 2030 737 — Senior notes – 5.875% due 2033 298 298 Senior notes – 4.75% due 2039 495 494 Senior notes – 4.35% due 2047 493 492 Senior notes – 4.20% due 2048 592 592 Senior notes – 4.90% due 2049 1,237 1,237 Mortgage – 5.70% due 2035 338 345 Term loan facility - two year 500 — Other 5 7 12,701 11,956 Less current portion 716 1,215 $ 11,985 $ 10,741 The senior notes in the table above are registered by the Company with the Securities and Exchange Commission and are not guaranteed. The Company has established a short-term debt financing program of up to $1.5 billion through the issuance of commercial paper. The proceeds from the issuance of commercial paper are used for general corporate purposes. The Company had no commercial paper outstanding at June 30, 2020 . Credit Facilities The Company and certain of its foreign subsidiaries have a multi-currency five-year unsecured revolving credit facility of $1.8 billion . The interest rate on this facility is based on LIBOR plus a fixed margin which varies with the Company's credit ratings. This facility expires in October 2023 and requires the Company to maintain certain coverage and leverage ratios which are tested quarterly. The facility includes a provision for determining a LIBOR successor rate in the event LIBOR reference rates are no longer available. In such case, the rate would be determined using an alternate reference rate that has been broadly accepted by the syndicated loan market in the United States in lieu of LIBOR (the “LIBOR successor rate”). If no LIBOR successor rate has been determined, the rate will be based on the higher of the rate announced publicly by Citibank, New York, NY, as its base rate or the fed funds rate plus a fixed margin. The Company had $1 billion of borrowings outstanding under this facility at March 31, 2020, which were repaid in full during the second quarter of 2020. There were no borrowings outstanding under this facility at June 30, 2020. In January 2020, the Company entered into two new term loan facilities: a $500 million one-year facility and a $500 million two-year facility. The interest rate on these facilities is based on LIBOR plus a fixed margin which varies with the Company's credit ratings. The facilities require the Company to maintain coverage ratios and leverage ratios consistent with the revolving credit facility discussed above. The facilities include a provision for determining a LIBOR successor rate in the event LIBOR reference rates are no longer available, which is expected to occur by the end of 2021.These facilities are expected to expire on or around the time that LIBOR is expected to be replaced by a successor rate. The Company had $1 billion of borrowings outstanding under these facilities at June 30, 2020. In April 2020, the Company entered into a new $1 billion unsecured revolving credit facility. The facility has similar coverage and leverage ratios as the facility discussed above. As of the date of this report the Company had no borrowings under this facility. Senior Notes In May 2020, the Company issued $750 million of 2.250% Senior Notes due 2030. The Company used the net proceeds to reduce outstanding short term borrowings. In March 2020, the Company repaid $500 million of maturing senior notes. In September 2019, the Company repaid $300 million of maturing senior notes. In connection with the closing of the JLT Transaction, the Company assumed approximately $1 billion of historical JLT indebtedness. In April and June of 2019, the Company repaid approximately $450 million and $553 million , respectively, representing all of JLT's debt it acquired upon the closing of the JLT Transaction. The Company incurred debt extinguishment costs of $32 million due to the debt repayments. Also in March 2019, the Company issued €550 million of 1.349% Senior Notes due 2026 and €550 million of 1.979% Senior Notes due 2030. In addition, the Company issued an additional $250 million of 4.375% Senior Notes due 2029, in March 2019. These notes constitute a further issuance of the 4.375% Senior Notes due 2029, of which $1.25 billion aggregate principal amount was issued in January 2019 (see below). After giving effect to the issuance of the notes, the Company has $1.5 billion aggregate principal amount of 4.375% Senior Notes due 2029. The Company used part of the net proceeds from these offerings, along with the $5 billion of Senior Notes issued in January 2019 (discussed above) primarily to fund the acquisition of JLT, including the payment of related fees and expenses, and to repay certain JLT indebtedness, as well as for general corporate purposes. In January 2019, the Company issued $700 million of 3.50% Senior Notes due 2020, $1 billion of 3.875% Senior Notes due 2024, $1.25 billion of 4.375% Senior Notes due 2029, $500 million of 4.75% Senior Notes due 2039, $1.25 billion of 4.90% Senior Notes due 2049 and $300 million of Floating Rate Senior Notes due 2021. The floating rate notes are based on LIBOR plus a fixed margin. These notes are due prior to the date that LIBOR is expected to be replaced by a successor rate, which is expected to occur in 2021. Fair Value of Short-term and Long-term Debt The estimated fair value of the Company’s short-term and long-term debt is provided below. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts shown below 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, 2020 December 31, 2019 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Short-term debt $ 1,216 $ 1,227 $ 1,215 $ 1,229 Long-term debt $ 11,985 $ 13,724 $ 10,741 $ 11,953 The fair value of the Company’s short-term debt consists primarily of borrowings from the term loan and revolving credit facilities and term debt maturing within the next year and its fair value approximates its carrying value. The estimated fair value of a primary portion of the Company's long-term debt is based on discounted future cash flows using current interest rates available for debt with similar terms and remaining maturities. Short-term and long-term debt would be classified as Level 2 in the fair value hierarchy.

Restructuring Costs

Restructuring Costs	6 Months Ended
	Jun. 30, 2020
Restructuring and Related Activities [Abstract]
Restructuring Costs	Restructuring Costs JLT Related Integration and Restructuring The Company is currently integrating JLT, which involves combining the business practices and co-locating colleagues in most geographies, rationalizing real estate leases around the world, realizing of synergies and migrating legacy JLT systems onto the Company's information technology environment and security protocols. The Company is also incurring cost for consulting fees related to integration management processes and legal fees related to rationalizing legal entity structures to reduce costs, mitigate risks and improve operational transparency. Costs will be recognized 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. Based on its current estimates, the Company expects to incur costs of approximately $700 million in connection with the integration and restructuring of the combined businesses, primarily related to severance, real estate rationalization, information technology rationalization, consulting fees related to the management of the integration processes and legal fees related to the rationalization of legal entity structures. The Company incurred $335 million in 2019 and $137 million in the first six months of 2020 and expects most of the remaining costs to be incurred in 2020, with a modest amount in 2021. These integration and restructuring plans may change during implementation, which may change our current cost and related savings estimates, as the Company continues to refine its detailed plans for each business and location. In connection with the JLT integration and restructuring, in the first six months of 2020 the Company incurred costs of $137 million : $100 million in RIS, $17 million in Consulting, and $20 million in Corporate. 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, 2019 through June 30, 2020 , is as follows: (In millions) Severance Real Estate Related Costs (a) Information Technology (a) Consulting and Other Outside Services (b) Total Liability at 1/1/19 $ — $ — $ — $ — $ — 2019 Charges 154 38 45 98 335 Cash payments (112 ) (14 ) (45 ) (94 ) (265 ) Non-cash charges — (19 ) — (4 ) (23 ) Liability at 12/31/19 $ 42 $ 5 $ — $ — $ 47 2020 Charges 29 31 37 40 137 Cash payments (56 ) (4 ) (34 ) (33 ) (127 ) Non-cash charges — (21 ) (3 ) — (24 ) Liability at 6/30/2020 $ 15 $ 11 $ — $ 7 $ 33 (a) Includes 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 During 2018 and 2019, Marsh initiated programs to simplify its organization structure and realign and rebrand certain of its businesses. The Company incurred severance and consulting costs of $2 million for the six month period ended June 30, 2020 , related to these initiatives. During the fourth quarter of 2018, Mercer initiated a program to restructure its business to further optimize the way Mercer operates, setting up the Company for a more fluid and nimble structure and operating model for the future. The Company incurred restructuring severance and consulting costs of $6 million for the six month period ended June 30, 2020 related to this initiative. In addition to the charges discussed above, the Company incurred costs of $12 million at Corporate in 2020 that reflect consulting costs related to the restructure of the Global HR function and adjustments to restructuring liabilities for future rent under non-cancellable leases. After further evaluation of our sublease assumptions, the Company recorded a ROU asset impairment charge of $11 million in the second quarter of 2020 to reflect the current market environment. The following details other restructuring liabilities for actions initiated prior to 2020 : (In millions) Liability at 1/1/19 Amounts Accrued Cash Paid Other Liability at 12/31/19 Amounts Accrued Cash Paid Other Liability at 6/30/2020 Severance $ 73 $ 73 $ (91 ) $ (4 ) $ 51 $ 6 $ (45 ) $ — $ 12 Future rent under non-cancelable leases and other costs 39 39 (21 ) (6 ) 51 14 (19 ) (1 ) $ 45 Total $ 112 $ 112 $ (112 ) $ (10 ) $ 102 $ 20 $ (64 ) $ (1 ) $ 57

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2020
Equity [Abstract]
Common Stock	Common Stock There were no repurchases of the Company's common stock during the first six months of 2020. The Company does not expect to repurchase shares for the remainder of 2020. 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. As of June 30, 2020 , the Company remained authorized to repurchase up to approximately $2.4 billion in shares of its common stock. There is no time limit on the authorization. During the first six months of 2019 the Company repurchased approximately 1.0 million shares of its common stock for consideration of $100 million . The Company issued approximately 2.8 million and 3.8 million shares related to stock compensation and employee stock purchase plans during the first six months of 2020 and 2019 , respectively.

Claims, Lawsuits And Other Cont

Claims, Lawsuits And Other Contingencies	6 Months Ended
	Jun. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Claims, Lawsuits, and Other Contingencies	Claims, Lawsuits and Other Contingencies Acquisition of Jardine Lloyd Thompson Group plc On April 1, 2019, the Company completed its previously announced acquisition of all of the outstanding shares of JLT. See Note 8 to the consolidated financial statements for additional information. Upon the consummation of the acquisition of JLT, the Company assumed the legal liabilities and became responsible for JLT’s litigation and regulatory exposures as of April 1, 2019. Litigation Matters The Company and its subsidiaries are subject to a significant number of claims, lawsuits and proceedings in the ordinary course of 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, investment advisory, and investment management services for corporate and public sector clients, 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 may 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 Group, a subsidiary of the Company, and other methods to estimate potential losses. A liability is established when a loss is both probable and reasonably estimable. The liability is reviewed quarterly and adjusted as developments warrant. In many cases, the Company has not recorded a liability, other than for legal fees to defend the claim, because we are unable, at the present time, to make a determination that a loss is both probable and reasonably estimable. To the extent that expected losses exceed our deductible in any policy year, the Company also records an asset for the amount that we expect to recover under any available third-party insurance programs. The Company has varying levels of third-party insurance coverage, with policy limits and coverage terms varying significantly by policy year. Governmental Inquiries and Enforcement Matters Our activities are regulated under the laws of the United States and its various states, the European Union and its member states, and the other jurisdictions in which the Company operates. Risk and Insurance Services Segment • In April 2017, the Financial Conduct Authority in the United Kingdom (the "FCA") commenced a civil competition investigation into the aviation insurance and reinsurance sector. In connection with that investigation, the FCA carried out an on-site inspection at the London offices of Marsh Limited, our Marsh and Guy Carpenter operating subsidiary in the United Kingdom, and JLT Specialty Ltd., JLT's U.K. operating subsidiary. The FCA indicated that it had reasonable grounds for suspecting that Marsh Limited, JLT Specialty Ltd. and other participants in the market had been sharing competitively sensitive information within the aviation insurance and reinsurance broking sector. In October 2017, the Company received a notice that the Directorate-General for Competition of the European Commission had commenced a civil investigation of a number of insurance brokers, including both Marsh and JLT, regarding "the exchange of commercially sensitive information between competitors in relation to aviation and aerospace insurance and reinsurance broking products and services in the European Economic Area ("EEA"), as well as possible coordination between competitors." In light of the action taken by the European Commission, the FCA informed Marsh Limited and JLT Specialty Ltd. that it had discontinued its investigation under U.K. competition law. In May 2018, the FCA advised that it would not be taking any further action with Marsh Limited or JLT Specialty Ltd. in connection with this matter. 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. 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. We are cooperating with the ongoing investigations. At this time, we are unable to predict the likely timing, outcome or ultimate impact of the foregoing investigations or any related 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. Consulting Segment In 2014, the FCA conducted a thematic review of the suitability of financial advice provided to individuals by a number of firms, including JLT’s employee benefits business, relating to enhanced transfer value ("ETV") pension transfers. In January 2015, the FCA notified JLT that it was commissioning a Skilled Person review of JLT’s ETV advice. In February 2019, prior to the completion of the acquisition, JLT recorded a gross liability of approximately £59 million (or approximately $77 million ) arising from the Skilled Person report and ETV review. Pending the outcome of the FCA’s review, and based on our review as of June 30, 2020, the Company has a gross liability of approximately £68 million (or approximately $83 million ) recorded on its consolidated balance sheet for the estimated liabilities and costs arising from this matter. We expect this gross liability to be partially offset by insurance and indemnification claims under existing arrangements. 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 were reinsured up to £40 million by a related party of River Thames. Payment of claims under the reinsurance agreement is collateralized by segregated assets held in a trust. As of June 30, 2020 , the reinsurance coverage exceeded the best estimate of the projected liability of the policies covered by the guarantee. To the extent River Thames or the reinsurer is unable to meet its obligations under those policies, a claimant may seek to recover from the Company under the guarantee. From 1980 to 1983, the Company owned indirectly the English & American Insurance Company ("E&A"), which was a member of the ILU. The ILU required the Company to guarantee a portion of E&A's obligations. After E&A became insolvent in 1993, the ILU agreed to discharge the guarantee in exchange for the Company's agreement to post an evergreen letter of credit that is available to pay claims by policyholders on certain E&A policies issued through the ILU and incepting between July 3, 1980 and October 6, 1983. Certain claims have been paid under the letter of credit and the Company anticipates that additional claimants may seek to recover against the letter of credit. * * * * The pending proceedings described above and other matters not explicitly described in this Note 17 on Claims, Lawsuits and Other Contingencies may expose the Company or its subsidiaries to liability for significant monetary damages, fines, penalties or other forms of relief. Where a loss is both probable and reasonably estimable, the Company establishes liabilities in accordance with 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, 2020
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 2019 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. Prior to being acquired by the Company, JLT operated in three segments: Specialty, Reinsurance and Employee Benefits. JLT operated in 41 countries, with significant revenue in the United Kingdom, Pacific, Asia and the United States. As of April 1, 2019, the historical JLT businesses were combined into MMC operations as follows: JLT Specialty is included by geography within Marsh, JLT Reinsurance is included in Guy Carpenter and the majority of JLT's Employee Benefits business was included in Mercer Health and Wealth. Selected information about the Company’s operating segments for the three and six -month periods ended June 30, 2020 and 2019 are as follows: Three Months Ended Six Months Ended (In millions) Revenue Operating Income (Loss) Revenue Operating Income (Loss) 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 2019– Risk and Insurance Services $ 2,574 (a) $ 517 $ 4,997 (c) $ 1,250 Consulting 1,800 (b) 278 3,473 (d) 557 Total Operating Segments 4,374 795 8,470 1,807 Corporate/Eliminations (25 ) (115 ) (50 ) (189 ) Total Consolidated $ 4,349 $ 680 $ 8,420 $ 1,618 (a) Includes inter-segment revenue of $4 million and $3 million in 2020 and 2019 , respectively, interest income on fiduciary funds of $9 million and $26 million in 2020 and 2019 , respectively, and equity method income of $14 million and $4 million in 2020 and 2019 , respectively. (b) Includes inter-segment revenue of $26 million and $22 million in 2020 and 2019 , respectively, interest income on fiduciary funds of less than $1 million and $1 million in 2020 and 2019 , respectively, and equity method income of $5 million in 2019 . (c) Includes inter-segment revenue of $5 million and $4 million in 2020 and 2019 , respectively, interest income on fiduciary funds of $32 million and $49 million in 2020 and 2019 , respectively, and equity method income of $13 million and $6 million in 2020 and 2019 , respectively. (d) Includes inter-segment revenue of $47 million and $46 million in 2020 and 2019 , respectively, interest income on fiduciary funds of less than $1 million and $2 million in 2020 and 2019 , respectively, and equity method income of $4 million and $10 million in 2020 and 2019 , respectively. Details of operating segment revenue for the three and six -month periods ended June 30, 2020 and 2019 are as follows: Three Months Ended Six Months Ended (In millions) 2020 2019 2020 2019 Risk and Insurance Services Marsh $ 2,168 $ 2,174 $ 4,244 $ 3,927 Guy Carpenter 435 400 1,270 1,070 Total Risk and Insurance Services 2,603 2,574 5,514 4,997 Consulting Mercer 1,149 1,260 2,400 2,415 Oliver Wyman Group 467 540 978 1,058 Total Consulting 1,616 1,800 3,378 3,473 Total Operating Segments 4,219 4,374 8,892 8,470 Corporate / Eliminations (30 ) (25 ) (52 ) (50 ) Total $ 4,189 $ 4,349 $ 8,840 $ 8,420

New Accounting Guidance

New Accounting Guidance	6 Months Ended
	Jun. 30, 2020
Accounting Standards Update and Change in Accounting Principle [Abstract]
New Accounting Guidance	New Accounting Guidance 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 is not expected to have a material 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 a 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. New Accounting Pronouncements Effective January 1, 2019: The following new accounting standard was adopted using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of January 1, 2019: Leases In February 2016, the FASB issued new guidance intended to improve financial reporting for leases. Under the new guidance, a lessee is required to recognize assets and liabilities for leases. Consistent with legacy GAAP, the recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee will depend on the classification of the lease as financing or operating. However, unlike legacy GAAP, which requires that only capital leases are recognized on the balance sheet, the new guidance requires that both operating and financing leases be recognized on the balance sheet. The Company adopted this new standard effective January 1, 2019, using a modified retrospective method, applying the new guidance as of the beginning of the year of adoption, with a cumulative effect of initially applying the guidance recognized as an adjustment to retained earnings at January 1, 2019. Therefore, prior period information has not been restated. The Company has elected the package of practical expedients, which among other things, allows historical lease classifications to be carried forward. The Company did not elect the hindsight practical expedient in determining lease term and impairment of an entity's ROU assets. On January 1, 2019, the Company recognized a lease liability of $1.9 billion and ROU asset of $1.7 billion , related to real estate operating leases. The ROU asset also reflected reclassification adjustments primarily from other liabilities related to existing deferred rent, unamortized lease incentives and restructuring liabilities of $0.2 billion upon adoption. There was no cumulative-effect adjustment required to be booked to retained earnings upon transition. The adoption of this standard did not have a material impact on our income statement as compared to prior periods. The following new accounting standards were adopted prospectively as of January 1, 2019: Derivatives and Hedging In August 2017, the FASB issued new guidance intended to refine and expand hedge accounting for both financial and commodity risks. The guidance creates more transparency around how economic results are presented in both the financial statements and the footnotes, as well as making targeted improvements to simplify the application of hedge accounting guidance. The Company adopted this guidance effective January 1, 2019. The adoption of this standard did not have an impact on the Company's financial position or results of operations. Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In February 2018, the FASB issued new guidance that allowed an entity to reclassify the stranded tax effects resulting from the Tax Cuts and Job Act (the "TCJA") from accumulated other comprehensive income ("AOCI") to retained earnings. The guidance is effective for the period beginning January 1, 2019. The Company elected not to reclassify the stranded income tax effects of the TCJA from AOCI to retained earnings. The adoption of this standard had no impact on the Company's financial position or results of operations. The Company’s accounting policy related to releasing income tax effects from AOCI follows the portfolio approach. New Accounting Pronouncements Not Yet Adopted 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 contract 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. Early adoption is permitted. The Company is currently evaluating the impact this standard will have on the Company’s financial position. 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 Company is currently evaluating the impact this standard will have on the Company’s financial position. In August 2018, the FASB issued new guidance that amends disclosures related to Defined Benefit Plans. The guidance removes disclosures that no longer are considered cost-beneficial, clarifies the specific requirements of certain disclosures, and adds disclosure requirements identified as relevant. The guidance must be applied on a retrospective basis. The guidance is effective for fiscal years ending after December 15, 2020. Early adoption is permitted. Adoption of this guidance will impact disclosures only and will not have an 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, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting	The consolidated financial statements included herein have been prepared by the Company pursuant to the rules and regulations of the Securities and Exchange Commission. While certain information and footnote 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 for interim filings, the Company believes that the information and disclosures presented are adequate to make such information and disclosures not misleading.
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.
Allowance for Credit Losses on Accounts Receivable	The Company’s policy for providing an allowance for current expected credit losses (“CECL”) on its accounts receivable is based on management’s best estimate of amounts that will be uncollectible primarily based on the Company’s historical experience of collections in its various businesses and other events that may affect the net realizable value of receivables. The charge related to expected credit losses was immaterial to the consolidated statement of income in the three and six month periods ended June 30, 2020.
Investments	The caption "Investment (loss) income" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds. The Company holds investments in certain private equity funds that are accounted for under 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 2020 was 26.2% compared with 37.4% in the second quarter of 2019 . The effective tax rates for the first six months of 2020 and 2019 were 24.9% and 28.2% . The rate in the second quarter and first six months of 2019 reflects discrete adjustments related to the JLT acquisition, including tax on the disposition of JLT’s aerospace business and nondeductible expenses incurred in connection with the JLT Transaction. The tax rates in all periods reflect the impact of discrete tax matters such as excess tax benefits related to share-based compensation, 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	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 reliant on estimates of future sub-lease income to be received and future contractual costs to be incurred. These costs are included in other operating expenses in the consolidated statements of income. Other costs related to 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 include treasury locks and 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 include assets and liabilities for contingent purchase consideration and the deal contingent foreign exchange contract (the "FX Contract") discussed in more detail in Note 11. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued 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 to four years. The fair value of the contingent purchase consideration asset and liability is estimated as the present value of future cash flows to be paid, based on projections of revenue and earnings and related targets of the acquired and disposed entities. Foreign Exchange Forward Contract Liabilities - Level 3 In connection with the JLT Transaction, the Company entered into the FX Contract, to hedge the risk of appreciation of the GBP-denominated purchase price. The Company settled the FX Contract on April 1, 2019, upon completion of the JLT Transaction.
New Accounting Pronouncements	New Accounting Guidance 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 is not expected to have a material 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 a 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. New Accounting Pronouncements Effective January 1, 2019: The following new accounting standard was adopted using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of January 1, 2019: Leases In February 2016, the FASB issued new guidance intended to improve financial reporting for leases. Under the new guidance, a lessee is required to recognize assets and liabilities for leases. Consistent with legacy GAAP, the recognition, measurement and presentation of expenses and cash flows arising from a lease by a lessee will depend on the classification of the lease as financing or operating. However, unlike legacy GAAP, which requires that only capital leases are recognized on the balance sheet, the new guidance requires that both operating and financing leases be recognized on the balance sheet. The Company adopted this new standard effective January 1, 2019, using a modified retrospective method, applying the new guidance as of the beginning of the year of adoption, with a cumulative effect of initially applying the guidance recognized as an adjustment to retained earnings at January 1, 2019. Therefore, prior period information has not been restated. The Company has elected the package of practical expedients, which among other things, allows historical lease classifications to be carried forward. The Company did not elect the hindsight practical expedient in determining lease term and impairment of an entity's ROU assets. On January 1, 2019, the Company recognized a lease liability of $1.9 billion and ROU asset of $1.7 billion , related to real estate operating leases. The ROU asset also reflected reclassification adjustments primarily from other liabilities related to existing deferred rent, unamortized lease incentives and restructuring liabilities of $0.2 billion upon adoption. There was no cumulative-effect adjustment required to be booked to retained earnings upon transition. The adoption of this standard did not have a material impact on our income statement as compared to prior periods. The following new accounting standards were adopted prospectively as of January 1, 2019: Derivatives and Hedging In August 2017, the FASB issued new guidance intended to refine and expand hedge accounting for both financial and commodity risks. The guidance creates more transparency around how economic results are presented in both the financial statements and the footnotes, as well as making targeted improvements to simplify the application of hedge accounting guidance. The Company adopted this guidance effective January 1, 2019. The adoption of this standard did not have an impact on the Company's financial position or results of operations. Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income In February 2018, the FASB issued new guidance that allowed an entity to reclassify the stranded tax effects resulting from the Tax Cuts and Job Act (the "TCJA") from accumulated other comprehensive income ("AOCI") to retained earnings. The guidance is effective for the period beginning January 1, 2019. The Company elected not to reclassify the stranded income tax effects of the TCJA from AOCI to retained earnings. The adoption of this standard had no impact on the Company's financial position or results of operations. The Company’s accounting policy related to releasing income tax effects from AOCI follows the portfolio approach. New Accounting Pronouncements Not Yet Adopted 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 contract 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. Early adoption is permitted. The Company is currently evaluating the impact this standard will have on the Company’s financial position. 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 Company is currently evaluating the impact this standard will have on the Company’s financial position. In August 2018, the FASB issued new guidance that amends disclosures related to Defined Benefit Plans. The guidance removes disclosures that no longer are considered cost-beneficial, clarifies the specific requirements of certain disclosures, and adds disclosure requirements identified as relevant. The guidance must be applied on a retrospective basis. The guidance is effective for fiscal years ending after December 15, 2020. Early adoption is permitted. Adoption of this guidance will impact disclosures only and will not have an impact on the Company's financial position or results of operations.

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2020
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) 2020 2019 2020 2019 Marsh: EMEA $ 597 $ 652 $ 1,351 $ 1,285 Asia Pacific 298 291 536 456 Latin America 99 116 190 194 Total International 994 1,059 2,077 1,935 U.S./Canada 1,167 1,097 2,145 1,958 Total Marsh 2,161 2,156 4,222 3,893 Guy Carpenter 433 392 1,260 1,055 Subtotal 2,594 2,548 5,482 4,948 Fiduciary interest income 9 26 32 49 Total Risk and Insurance Services $ 2,603 $ 2,574 $ 5,514 $ 4,997 Mercer: Wealth $ 561 $ 613 $ 1,153 $ 1,156 Health 432 458 918 900 Career 156 189 329 359 Total Mercer 1,149 1,260 2,400 2,415 Oliver Wyman 467 540 978 1,058 Total Consulting $ 1,616 $ 1,800 $ 3,378 $ 3,473
Contract with Customer, Asset and Liability	The following schedule provides contract assets and contract liabilities information from contracts with customers. (In millions) June 30, 2020 December 31, 2019 Contract Assets $ 298 $ 207 Contract Liabilities $ 696 $ 593

Per Share Data (Tables)

Per Share Data (Tables)	6 Months Ended
	Jun. 30, 2020
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) 2020 2019 2020 2019 Net income before non-controlling interests $ 580 $ 344 $ 1,347 $ 1,071 Less: Net income attributable to non-controlling interests 8 12 21 23 Net income attributable to the Company $ 572 $ 332 $ 1,326 $ 1,048 Basic weighted average common shares outstanding 506 507 505 506 Dilutive effect of potentially issuable common shares 5 5 5 5 Diluted weighted average common shares outstanding 511 512 510 511 Average stock price used to calculate common stock equivalents $ 101.17 $ 95.74 $ 104.14 $ 92.14

Supplemental Disclosures to t_2

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Tables)	6 Months Ended
	Jun. 30, 2020
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, 2020 and 2019 . (In millions) 2020 2019 Assets acquired, excluding cash $ 752 $ 8,593 Liabilities assumed (29 ) (2,718 ) Non-controlling interests assumed — (309 ) Contingent/deferred purchase consideration (161 ) (66 ) Net cash outflow for current year acquisitions $ 562 $ 5,500 (In millions) 2020 2019 Interest paid $ 248 $ 141 Income taxes paid, net of refunds $ 227 $ 327

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2020
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, 2020 and 2019 , 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, 2020 $ (3,374 ) $ (2,473 ) $ (5,847 ) Other comprehensive 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 April 1, 2019 $ (2,990 ) $ (1,600 ) $ (4,590 ) Other comprehensive income before reclassifications 29 15 44 Amounts reclassified from accumulated other comprehensive income 19 — 19 Net current period other comprehensive income 48 15 63 Balance as of June 30, 2019 $ (2,942 ) $ (1,585 ) $ (4,527 ) (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 (loss) income 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 ) (In millions) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2018 $ (2,953 ) $ (1,694 ) $ (4,647 ) Other comprehensive income (loss) before reclassifications (30 ) 109 79 Amounts reclassified from accumulated other comprehensive income 41 — 41 Net current period other comprehensive income 11 109 120 Balance as of June 30, 2019 $ (2,942 ) $ (1,585 ) $ (4,527 )
Schedule of Components of Comprehensive Income (Loss)	The components of other comprehensive income (loss) for the three and six -month periods ended June 30, 2020 and 2019 are as follows: Three Months Ended June 30, 2020 2019 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ 241 $ 4 $ 237 $ 13 $ (2 ) $ 15 Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (1 ) — (1 ) — — — Net actuarial losses (a) 40 8 32 26 6 20 Effect of remeasurement (a) — — — (1 ) — (1 ) Subtotal 39 8 31 25 6 19 Foreign currency translation adjustments (5 ) (2 ) (3 ) 38 9 29 Pension/post-retirement plans gains 34 6 28 63 15 48 Other comprehensive income $ 275 $ 10 $ 265 $ 76 $ 13 $ 63 (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, 2020 2019 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (700 ) $ (7 ) $ (693 ) $ 109 $ — $ 109 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) 80 19 61 52 12 40 Effect of remeasurement (a) — — — (1 ) — (1 ) Effect of settlement (a) — — — 4 1 3 Subtotal 79 19 60 54 13 41 Foreign currency translation adjustments 130 24 106 (34 ) (4 ) (30 ) Pension/post-retirement plans gains 209 43 166 20 9 11 Other comprehensive (loss) income $ (491 ) $ 36 $ (527 ) $ 129 $ 9 $ 120 (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, 2020
Business Combinations [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 2020 based on the estimated fair values for the acquisitions as of their respective acquisition dates: Acquisitions through June 30, 2020 (In millions) Cash 576 Estimated fair value of deferred/contingent consideration 161 Total consideration $ 737 Allocation of purchase price: Cash and cash equivalents 14 Accounts receivable, net 28 Fixed assets, net 16 Other intangible assets 277 Goodwill 466 Deferred tax assets (43 ) Other assets 8 Total assets acquired 766 Current liabilities 19 Other liabilities 10 Total liabilities assumed 29 Net assets acquired $ 737
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	The following chart provides information about intangible assets acquired during 2020 : Intangible assets through June 30, 2020 (In millions) Amount Weighted Average Amortization Period Client relationships $ 255 13.3 years Other 22 4.5 years $ 277
Pro-Forma Information	The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during 2020 and 2019. In accordance with accounting guidance related to pro-forma disclosures, the information presented for current year acquisitions is as if they occurred on January 1, 2019 and reflects acquisitions made in 2019 as if they occurred on January 1, 2018. The unaudited pro-forma information adjusts for the effects of amortization of acquired intangibles and additional interest expense related to the issuance of debt related to the JLT Transaction. 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) 2020 2019 2020 2019 Revenue $ 4,189 $ 4,395 $ 8,891 $ 8,963 Net income attributable to the Company $ 574 $ 488 $ 1,328 $ 1,146 Basic net income per share attributable to the Company $ 1.13 $ 0.96 $ 2.63 $ 2.26 Diluted net income per share attributable to the Company $ 1.12 $ 0.95 $ 2.60 $ 2.24

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	6 Months Ended
	Jun. 30, 2020
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) 2020 2019 Balance as of January 1, $ 14,671 $ 9,599 Goodwill acquired 466 4,895 Other adjustments (a) (340 ) (15 ) Balance at June 30, $ 14,797 $ 14,479 (a) Primarily reflects the impact of foreign exchange.
Amortized Intangible Assets	The gross cost and accumulated amortization of identified intangible assets at June 30, 2020 and December 31, 2019 are as follows: June 30, 2020 December 31, 2019 (In millions) Gross Cost Accumulated Amortization Net Carrying Amount Gross Cost Accumulated Amortization Net Carrying Amount Client Relationships $ 3,592 $ 1,002 $ 2,590 $ 3,494 $ 897 $ 2,597 Other (a) 390 219 171 380 203 177 Amortized intangibles $ 3,982 $ 1,221 $ 2,761 $ 3,874 $ 1,100 $ 2,774 (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 2020 (excludes amortization through June 30, 2020) $ 181 2021 347 2022 321 2023 296 2024 282 Subsequent years 1,334 $ 2,761

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2020
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, 2020 and December 31, 2019 . Identical Assets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Total (In millions) 06/30/20 12/31/19 06/30/20 12/31/19 06/30/20 12/31/19 06/30/20 12/31/19 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 59 $ 4 $ — $ — $ — $ — $ 59 $ 4 Mutual funds (a) 155 166 — — — — 155 166 Money market funds (b) 530 55 — — — — 530 55 Other equity investment (a) — — 8 8 — — 8 8 Contingent purchase consideration asset (c) — — — — 64 84 64 84 Total assets measured at fair value $ 744 $ 225 $ 8 $ 8 $ 64 $ 84 $ 816 $ 317 Fiduciary Assets: U.S. Treasury Bills $ 55 $ 40 $ — $ — $ — $ — $ 55 $ 40 Money market funds 79 360 — — — — 79 360 Total fiduciary assets measured at fair value $ 134 $ 400 $ — $ — $ — $ — $ 134 $ 400 Liabilities: Contingent purchase consideration liability (d) $ — $ — $ — $ — $ 233 $ 225 $ 233 $ 225 Total liabilities measured at fair value $ — $ — $ — $ — $ 233 $ 225 $ 233 $ 225 (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 at June 30, 2020 and other assets at December 31, 2019 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 table below 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, 2020 and 2019 : Three Months Ended Six Months Ended (In millions) 2020 2019 2020 2019 Balance at beginning of period $ 239 $ 454 $ 225 $ 508 Net Additions 66 29 96 40 Payments (65 ) (10 ) (78 ) (45 ) Revaluation Impact (11 ) 9 (10 ) 20 Change in fair value of the FX contract — (283 ) — (325 ) Other (a) 4 (3 ) — (2 ) Balance at June 30, $ 233 $ 196 $ 233 $ 196 (a) Primarily reflects the impact of foreign exchange.

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2020
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) 2020 2019 2020 2019 Lease Cost: Operating lease cost $ 97 $ 100 $ 189 $ 182 Short-term lease cost 1 2 2 3 Variable lease cost 27 39 64 76 Sublease income (5 ) (4 ) (10 ) (8 ) Net lease cost $ 120 $ 137 $ 245 $ 253 Other information: Operating cash outflows from operating leases $ 197 187 Right of use assets obtained in exchange for new operating lease liabilities $ 129 67 Weighted-average remaining lease term – real estate 8.53 years 8.99 years Weighted-average discount rate – real estate leases 3.05 % 3.08 %
Future Minimum Lease Payments for Operating Leases	Future minimum lease payments for the Company’s operating leases as of June 30, 2020 are as follows: Payment Dates (In millions) Real Estate Leases Remainder of 2020 $ 208 2021 373 2022 348 2023 303 2024 259 2025 233 Subsequent years 822 Total future lease payments 2,546 Less: Imputed interest (312 ) Total $ 2,234 Current lease liabilities $ 332 Long-term lease liabilities 1,902 Total lease liabilities $ 2,234 Note: Table excludes obligations for leases with original terms of 12 months or less which have not been recognized as a right to use asset or liability in the consolidated balance sheets.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	6 Months Ended
	Jun. 30, 2020
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 Benefits Post-retirement Benefits For the Three Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 9 $ 10 $ — $ — Interest cost 104 121 — — Expected return on plan assets (207 ) (217 ) — — Recognized actuarial loss 40 26 — — Net periodic benefit credit $ (54 ) $ (60 ) $ — $ — Combined U.S. and significant non-U.S. Plans Pension Benefits Post-retirement Benefits For the Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 17 $ 18 $ — $ — Interest cost 210 240 1 1 Expected return on plan assets (417 ) (430 ) — — Amortization of prior service credit — — (1 ) (1 ) Recognized actuarial loss 80 52 — — Net periodic benefit credit $ (110 ) $ (120 ) $ — $ — Settlement loss — 4 — — Total credit $ (110 ) $ (116 ) $ — $ — 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) 2020 2019 2020 2019 Compensation and benefits expense (Operating income) $ 9 $ 10 $ — $ — Other net benefit credits (63 ) (70 ) — — Total (credit) cost $ (54 ) $ (60 ) $ — $ — 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) 2020 2019 2020 2019 Compensation and benefits expense (Operating income) $ 17 $ 18 $ — $ — Other net benefit credits (127 ) (134 ) — — Total credit $ (110 ) $ (116 ) $ — $ — U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2020 2019 2020 2019 Interest cost $ 54 $ 60 $ — $ — Expected return on plan assets (87 ) (85 ) — — Recognized actuarial loss 18 11 — — Net periodic benefit credit $ (15 ) $ (14 ) $ — $ — U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Interest cost $ 107 $ 120 $ — $ — Expected return on plan assets (173 ) (171 ) — — Recognized actuarial loss (credit) 36 22 — — Net periodic benefit credit $ (30 ) $ (29 ) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 9 $ 10 $ — $ — Interest cost 50 61 — — Expected return on plan assets (120 ) (132 ) — — Recognized actuarial loss 22 15 — — Net periodic benefit credit $ (39 ) $ (46 ) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2020 2019 2020 2019 Service cost $ 17 $ 18 $ — $ — Interest cost 103 120 1 1 Expected return on plan assets (244 ) (259 ) — — Amortization of prior service credit — — (1 ) (1 ) Recognized actuarial loss 44 30 — — Net periodic benefit credit $ (80 ) $ (91 ) $ — $ — Settlement loss — 4 — — Total credit $ (80 ) $ (87 ) $ — $ —
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, 2020 2019 2020 2019 Weighted average assumptions: Expected return on plan assets 5.31 % 5.74 % — — Discount rate 2.57 % 3.48 % 2.72 % 3.65 % Rate of compensation increase 1.76 % 1.74 % — —

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	The Company’s outstanding debt is as follows: (In millions) June 30, December 31, Short-term: Term loan facility - one year 500 — Current portion of long-term debt 716 1,215 1,216 1,215 Long-term: Senior notes – 2.35% due 2020 — 500 Senior notes – 3.50% due 2020 699 698 Senior notes – 4.80% due 2021 499 499 Senior notes - Floating rate due 2021 299 298 Senior notes – 2.75% due 2022 499 498 Senior notes – 3.30% due 2023 349 349 Senior notes – 4.05% due 2023 249 249 Senior notes – 3.50% due 2024 598 597 Senior notes – 3.875% due 2024 994 994 Senior notes – 3.50% due 2025 497 497 Senior notes – 1.349% due 2026 615 609 Senior notes – 3.75% due 2026 597 597 Senior notes – 4.375% due 2029 1,499 1,499 Senior notes – 1.979% due 2030 612 607 Senior notes – 2.250% due 2030 737 — Senior notes – 5.875% due 2033 298 298 Senior notes – 4.75% due 2039 495 494 Senior notes – 4.35% due 2047 493 492 Senior notes – 4.20% due 2048 592 592 Senior notes – 4.90% due 2049 1,237 1,237 Mortgage – 5.70% due 2035 338 345 Term loan facility - two year 500 — Other 5 7 12,701 11,956 Less current portion 716 1,215 $ 11,985 $ 10,741
Estimated Fair Value Of Significant Financial Instruments	The estimated fair value of the Company’s short-term and long-term debt is provided below. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts shown below 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, 2020 December 31, 2019 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Short-term debt $ 1,216 $ 1,227 $ 1,215 $ 1,229 Long-term debt $ 11,985 $ 13,724 $ 10,741 $ 11,953

Restructuring Costs (Tables)

Restructuring Costs (Tables)	6 Months Ended
	Jun. 30, 2020
Restructuring and Related Activities [Abstract]
Restructuring Activities	The following details other restructuring liabilities for actions initiated prior to 2020 : (In millions) Liability at 1/1/19 Amounts Accrued Cash Paid Other Liability at 12/31/19 Amounts Accrued Cash Paid Other Liability at 6/30/2020 Severance $ 73 $ 73 $ (91 ) $ (4 ) $ 51 $ 6 $ (45 ) $ — $ 12 Future rent under non-cancelable leases and other costs 39 39 (21 ) (6 ) 51 14 (19 ) (1 ) $ 45 Total $ 112 $ 112 $ (112 ) $ (10 ) $ 102 $ 20 $ (64 ) $ (1 ) $ 57 Details of the JLT integration and restructuring activity from January 1, 2019 through June 30, 2020 , is as follows: (In millions) Severance Real Estate Related Costs (a) Information Technology (a) Consulting and Other Outside Services (b) Total Liability at 1/1/19 $ — $ — $ — $ — $ — 2019 Charges 154 38 45 98 335 Cash payments (112 ) (14 ) (45 ) (94 ) (265 ) Non-cash charges — (19 ) — (4 ) (23 ) Liability at 12/31/19 $ 42 $ 5 $ — $ — $ 47 2020 Charges 29 31 37 40 137 Cash payments (56 ) (4 ) (34 ) (33 ) (127 ) Non-cash charges — (21 ) (3 ) — (24 ) Liability at 6/30/2020 $ 15 $ 11 $ — $ 7 $ 33 (a) Includes 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.

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2020
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, 2020 and 2019 are as follows: Three Months Ended Six Months Ended (In millions) Revenue Operating Income (Loss) Revenue Operating Income (Loss) 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 2019– Risk and Insurance Services $ 2,574 (a) $ 517 $ 4,997 (c) $ 1,250 Consulting 1,800 (b) 278 3,473 (d) 557 Total Operating Segments 4,374 795 8,470 1,807 Corporate/Eliminations (25 ) (115 ) (50 ) (189 ) Total Consolidated $ 4,349 $ 680 $ 8,420 $ 1,618 (a) Includes inter-segment revenue of $4 million and $3 million in 2020 and 2019 , respectively, interest income on fiduciary funds of $9 million and $26 million in 2020 and 2019 , respectively, and equity method income of $14 million and $4 million in 2020 and 2019 , respectively. (b) Includes inter-segment revenue of $26 million and $22 million in 2020 and 2019 , respectively, interest income on fiduciary funds of less than $1 million and $1 million in 2020 and 2019 , respectively, and equity method income of $5 million in 2019 . (c) Includes inter-segment revenue of $5 million and $4 million in 2020 and 2019 , respectively, interest income on fiduciary funds of $32 million and $49 million in 2020 and 2019 , respectively, and equity method income of $13 million and $6 million in 2020 and 2019 , respectively. (d) Includes inter-segment revenue of $47 million and $46 million in 2020 and 2019 , respectively, interest income on fiduciary funds of less than $1 million and $2 million in 2020 and 2019 , respectively, and equity method income of $4 million and $10 million in 2020 and 2019 , respectively.
Details of Operating Segment Revenue	Details of operating segment revenue for the three and six -month periods ended June 30, 2020 and 2019 are as follows: Three Months Ended Six Months Ended (In millions) 2020 2019 2020 2019 Risk and Insurance Services Marsh $ 2,168 $ 2,174 $ 4,244 $ 3,927 Guy Carpenter 435 400 1,270 1,070 Total Risk and Insurance Services 2,603 2,574 5,514 4,997 Consulting Mercer 1,149 1,260 2,400 2,415 Oliver Wyman Group 467 540 978 1,058 Total Consulting 1,616 1,800 3,378 3,473 Total Operating Segments 4,219 4,374 8,892 8,470 Corporate / Eliminations (30 ) (25 ) (52 ) (50 ) Total $ 4,189 $ 4,349 $ 8,840 $ 8,420

Nature of Operations (Details)

Nature of Operations (Details) colleague in Thousands, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020USD ($)colleaguecountry	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)colleaguecountry	Jun. 30, 2019USD ($)
Nature of Operations [Line Items]
Entity number of colleagues | colleague	76		76
Revenue	$ 4,189	$ 4,349	$ 8,840	$ 8,420
Number of countries in which entity operates (more than) | country	130		130
Marsh & McLennan Companies, Inc.
Nature of Operations [Line Items]
Revenue			$ 17,000

Principles of Consolidation A_3

Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 201,000,000		$ 201,000,000		$ 197,000,000
Equity method investments lag period			3 months
Gain (loss) on investment income, net	(31,000,000)	$ 8,000,000	$ (33,000,000)	$ 13,000,000
Gain (loss) on equity securities	$ (2,000,000)	$ 3,000,000	$ (3,000,000)	$ 6,000,000
Effective tax rate (as a percent)	26.20%	37.40%	24.90%	28.20%
Unrecognized tax benefits	$ 79,000,000		$ 79,000,000		$ 86,000,000
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	12,000,000		12,000,000
Private Equity Funds
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Equity method income	(6,000,000)	$ 5,000,000	(7,000,000)	$ 7,000,000
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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue	$ 4,189	$ 4,349	$ 8,840	$ 8,420
Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	2,603	2,574	5,514	4,997
Fiduciary interest income	9	26	32	49
Risk and Insurance Services Segment | EMEA
Disaggregation of Revenue [Line Items]
Revenue	597	652	1,351	1,285
Risk and Insurance Services Segment | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	298	291	536	456
Risk and Insurance Services Segment | Latin America
Disaggregation of Revenue [Line Items]
Revenue	99	116	190	194
Risk and Insurance Services Segment | Total International
Disaggregation of Revenue [Line Items]
Revenue	994	1,059	2,077	1,935
Risk and Insurance Services Segment | U.S./Canada
Disaggregation of Revenue [Line Items]
Revenue	1,167	1,097	2,145	1,958
Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,616	1,800	3,378	3,473
Consulting Segment | Wealth
Disaggregation of Revenue [Line Items]
Revenue	561	613	1,153	1,156
Consulting Segment | Health
Disaggregation of Revenue [Line Items]
Revenue	432	458	918	900
Consulting Segment | Career
Disaggregation of Revenue [Line Items]
Revenue	156	189	329	359
Marsh Insurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	2,161	2,156	4,222	3,893
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	433	392	1,260	1,055
Marsh & Guy Carpenter | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	2,594	2,548	5,482	4,948
Mercer Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,149	1,260	2,400	2,415
Oliver Wyman Group Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 467	$ 540	$ 978	$ 1,058

Revenue - Contract Assets and C

Revenue - Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Revenue from Contract with Customer [Abstract]
Contract Assets	$ 298	$ 207
Contract Liabilities	$ 696	$ 593

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Jun. 30, 2019
Disaggregation of Revenue [Line Items]
Revenue recognized that was included in the contract liability balance at the beginning of the period		$ 418	$ 307
Performance obligation satisfied in previous period		67	$ 36
Revenue reduction for estimated commission revenue	$ 36
Marsh Insurance Group
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	51	51
Mercer Consulting Group
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	220	220
Oliver Wyman Group Consulting Group
Disaggregation of Revenue [Line Items]
Revenue, remaining performance obligation	2	$ 2
Risk and Insurance Services Segment | Marsh Insurance Group
Disaggregation of Revenue [Line Items]
Revenue reduction for estimated commission revenue	33
Consulting Segment | Mercer Consulting Group | Health
Disaggregation of Revenue [Line Items]
Revenue reduction for estimated commission revenue	$ 3

Revenue - Estimated Revenue Exp

Revenue - Estimated Revenue Expected to Be Recognized Related to Performance Obligations (Details) $ in Millions	Jun. 30, 2020USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 146
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)	1 year
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	$ 71
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	$ 36
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	$ 14
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	$ 6
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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 11,600		$ 11,600		$ 8,900
Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	9	$ 26	32	$ 49
Operating Segments | Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	9	26	32	49
Operating Segments | Consulting Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	$ 1	$ 1	$ 1	$ 2

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Earnings Per Share [Abstract]
Net income before non-controlling interests	$ 580	$ 344	$ 1,347	$ 1,071
Less: Net income attributable to non-controlling interests	8	12	21	23
Net income attributable to the Company	$ 572	$ 332	$ 1,326	$ 1,048
Basic weighted average common shares outstanding (in shares)	506	507	505	506
Dilutive effect of potentially issuable common shares (in shares)	5	5	5	5
Diluted weighted average common shares outstanding (in shares)	511	512	510	511
Average stock price used to calculate common stock equivalents (in dollars per share)	$ 101.17	$ 95.74	$ 104.14	$ 92.14

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, 2020	Jun. 30, 2019
Supplemental Cash Flow Information [Abstract]
Assets acquired, excluding cash	$ 752	$ 8,593
Liabilities assumed	(29)	(2,718)
Non-controlling interests assumed	0	(309)
Contingent/deferred purchase consideration	(161)	(66)
Net cash outflow for current year acquisitions	562	5,500
Interest paid	248	141
Income taxes paid, net of refunds	$ 227	$ 327

Supplemental Disclosures to t_4

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition	$ 69	$ 39
Deferred purchase consideration from prior years' acquisitions	27	23
Contingent consideration from prior year's acquisitions	42	16
Expense for adjustments related to contingent consideration liabilities	6	20
Payment of contingent consideration	36	29
Non-cash issuance of common stock	213	162
Stock-based compensation expense, equity awards	$ 147	$ 117

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period			$ 7,943
Other comprehensive income before reclassifications	$ 234	$ 44	(587)	$ 79
Amounts reclassified from accumulated other comprehensive income	31	19	60	41
Other comprehensive income (loss), net of tax	265	63	(527)	120
Balance, end of period	8,392	8,337	8,392	8,337
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(5,847)	(4,590)	(5,055)	(4,647)
Other comprehensive income (loss), net of tax	265	63	(527)	120
Balance, end of period	(5,582)	(4,527)	(5,582)	(4,527)
Pension/Post-Retirement Plans Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(3,374)	(2,990)	(3,512)	(2,953)
Other comprehensive income before reclassifications	(3)	29	106	(30)
Amounts reclassified from accumulated other comprehensive income	31	19	60	41
Other comprehensive income (loss), net of tax	28	48	166	11
Balance, end of period	(3,346)	(2,942)	(3,346)	(2,942)
Foreign Currency Translation Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(2,473)	(1,600)	(1,543)	(1,694)
Other comprehensive income before reclassifications	237	15	(693)	109
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	237	15	(693)	109
Balance, end of period	$ (2,236)	$ (1,585)	$ (2,236)	$ (1,585)

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Equity [Abstract]
Foreign currency translation adjustments, Pre-Tax	$ 241	$ 13	$ (700)	$ 109
Foreign currency translation adjustments, Tax	4	(2)	(7)	0
Foreign currency translation adjustments, Net of Tax	237	15	(693)	109
Pension/post-retirement plans:
Prior services credits, Pre-Tax	(1)	0	(1)	(1)
Prior service credits, Tax	0	0	0	0
Prior service credits, Net of Tax	(1)	0	(1)	(1)
Net actuarial loss, Pre-Tax	40	26	80	52
Net actuarial loss, Tax	8	6	19	12
Net actuarial loss, Net of Tax	32	20	61	40
Effect of remeasurement, Pre-tax	0	(1)	0	(1)
Effect of remeasurement, Tax	0	0	0	0
Effect of remeasurement, Net of Tax	0	(1)	0	(1)
Effect of settlement, Pre-tax			0	4
Effect of settlement, Tax			0	1
Effect of settlement, Net of Tax			0	3
Subtotal, Pre-Tax	39	25	79	54
Subtotal, Tax	8	6	19	13
Subtotal, Net of Tax	31	19	60	41
Foreign currency translation adjustment, Pre-Tax	(5)	38	130	(34)
Foreign currency translation adjustment, Tax	(2)	9	24	(4)
Foreign currency translation adjustment, Net of Tax	(3)	29	106	(30)
Pension/post-retirement plans gains, Pre-Tax	34	63	209	20
Pension/post-retirement plans gains, Tax	6	15	43	9
Pension/post-retirement plans gains, Net of Tax	28	48	166	11
Other comprehensive income (loss), before tax	275	76	(491)	129
Other comprehensive (loss) income, Tax	10	13	36	9
Other comprehensive income (loss), net of tax	$ 265	$ 63	$ (527)	$ 120

Acquisitions and Dispositions_2

Acquisitions and Dispositions (Narrative) (Details) £ / shares in Units, shares in Millions, $ in Millions, £ in Billions	Jun. 01, 2019USD ($)	Apr. 01, 2019USD ($)$ / £	Apr. 01, 2019GBP (£)£ / shares$ / £	Sep. 20, 2018GBP (£)	May 31, 2020shares	Feb. 29, 2020shares	Jun. 30, 2020USD ($)shares	Sep. 30, 2019USD ($)	Jun. 30, 2019USD ($)	Jun. 30, 2020USD ($)acquisitionshares	Jun. 30, 2019USD ($)	Dec. 31, 2019USD ($)shares	Dec. 31, 2019acquisitionshares	Jan. 01, 2019
Business Acquisition [Line Items]
Total consideration										$ 737	$ 5,925
Cash paid										576	5,859
Estimated fair value of deferred/contingent consideration										161	66
Deferred purchase consideration from prior years' acquisitions										27	23
Contingent consideration from prior year's acquisitions										42	16
Assumption of debt										29	2,718
Payments to acquire outstanding minority interests of subsidiaries										0	91	$ 79
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions										27	23
Contingent consideration from prior year's acquisitions										78	45
Jardine Lloyd Thompson Group plc
Business Acquisition [Line Items]
Total consideration | £				£ 5.2
Business acquisition, share price (in gbp per share) | £ / shares			£ 19.15
Equity interests issued and issuable		$ 5,600	£ 4.3
Business combination, exchange rate | $ / £		1.31	1.31
Assumption of debt		$ 1,000
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration										737
Cash paid										576
Estimated fair value of deferred/contingent consideration										161
Revenue related to acquisitions							$ 48		$ 486	63	496
Operating (loss) income related to acquisitions							$ 7		$ 16	$ 11	$ 18
Risk and Insurance Services Segment
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition										4			5
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)										2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)										4 years
Alexander Forbes Group Holdings Limited
Business Acquisition [Line Items]
Equity method investment, shares owned | shares												443	443
Number of shares sold (shares) | shares					193	49
Marsh India
Business Acquisition [Line Items]
Percentage of ownership in equity investment												26.00%	26.00%	49.00%
Certain Businesses Primarily in the U.S., U.K. and Canada
Business Acquisition [Line Items]
Disposal group, consideration										$ 93
Specialty Business and Large Market Health and Defined Benefit Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Disposal group, consideration								$ 60
Alexander Forbes Group Holdings Limited
Business Acquisition [Line Items]
Investment owned, shares | shares							201			201
JLT’s Global Aerospace Business | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Business Acquisition [Line Items]
Disposal group, consideration	$ 165
Contingent consideration receivable	$ 65

Acquisitions and Dispositions_3

Acquisitions and Dispositions (Allocation Of Acquisition Costs) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Business Acquisition [Line Items]
Cash	$ 576	$ 5,859
Estimated fair value of deferred/contingent consideration	161	66
Total consideration	737	5,925
Allocation of purchase price:
Goodwill	14,797	$ 14,479	$ 14,671	$ 9,599
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	576
Estimated fair value of deferred/contingent consideration	161
Total consideration	737
Allocation of purchase price:
Cash and cash equivalents	14
Accounts receivable, net	28
Fixed assets, net	16
Other intangible assets	277
Goodwill	466
Deferred tax assets	(43)
Other assets	8
Total assets acquired	766
Current liabilities	19
Other liabilities	10
Total liabilities assumed	29
Net assets acquired	$ 737

Acquisitions and Dispositions_4

Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 277
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 255
Finite-lived intangible assets, remaining amortization period	13 years 3 months 18 days
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 22
Finite-lived intangible assets, remaining amortization period	4 years 6 months

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Business Combinations [Abstract]
Revenue	$ 4,189	$ 4,395	$ 8,891	$ 8,963
Net income attributable to the Company	$ 574	$ 488	$ 1,328	$ 1,146
Basic net income per share attributable to the Company (in dollars per share)	$ 1.13	$ 0.96	$ 2.63	$ 2.26
Diluted net income per share attributable to the Company (in dollars per share)	$ 1.12	$ 0.95	$ 2.60	$ 2.24

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2018
Segment Reporting Information [Line Items]
Goodwill acquired	$ 466	$ 4,895
Goodwill	14,797	14,479	$ 14,671	$ 9,599
Aggregate amortization expense	174	$ 151
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill acquired	466
Goodwill, expected tax deductible amount	141
Goodwill	11,200
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	$ 3,600

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Goodwill [Roll Forward]
Balance as of January 1,	$ 14,671	$ 9,599
Goodwill acquired	466	4,895
Other adjustments	(340)	(15)
Balance at June 30,	$ 14,797	$ 14,479

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Finite-Lived Intangible Assets [Line Items]
Gross Cost	$ 3,982	$ 3,874
Accumulated Amortization	1,221	1,100
Net Carrying Amount	2,761	2,774
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost	3,592	3,494
Accumulated Amortization	1,002	897
Net Carrying Amount	2,590	2,597
Other
Finite-Lived Intangible Assets [Line Items]
Gross Cost	390	380
Accumulated Amortization	219	203
Net Carrying Amount	$ 171	$ 177

Goodwill And Other Intangible_5

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
2020 (excludes amortization through June 30, 2020)	$ 181
2021	347
2022	321
2023	296
2024	282
Subsequent years	1,334
Net Carrying Amount	$ 2,761	$ 2,774

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	Apr. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net charge (credit) for adjustments related to acquisition related accounts								$ (10)
Increase in fair value of contingent consideration due to 5% increase in projections								14
Decrease in fair value of contingent consideration due to 5% decrease in projections								16
Carrying value of investment					$ 264			264		$ 434
Equity securities					72			72		19
Gain (loss) on equity securities					(2)	$ 3		(3)	$ 6
Equity investments without readily determinable market value					45			$ 45		67
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					171			$ 171		183
Private Equity Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment					93			93		$ 107
Equity method income (loss)					(6)	5		(7)	$ 7
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Equity method investment, shares owned										443
Number of shares sold (shares)	193	49
Investments, fair value					$ 55			55
BenefitFocus
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sale of other investments			$ 17	$ 132			$ 115
Payscale
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Proceeds from sale of other investments						$ 47
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Change in contingent purchase consideration								16
Increase in fair value of contingent consideration due to 5% increase in projections								6
Decrease in fair value of contingent consideration due to 5% decrease in projections								$ 6
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount)					$ 1			$ 1
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment owned, shares					201			201

Fair Value Measurements (Assets

Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Financial instruments owned:
Exchange traded equity securities	$ 72	$ 19
Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	816	317
Fiduciary Assets:
Fiduciary assets	134	400
Liabilities:
Total liabilities measured at fair value	233	225
Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	744	225
Fiduciary Assets:
Fiduciary assets	134	400
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	64	84
Fiduciary Assets:
Fiduciary assets	0	0
Liabilities:
Total liabilities measured at fair value	233	225
US Treasury Bills | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	55	40
US Treasury Bills | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	55	40
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	79	360
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	79	360
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	59	4
Mutual funds	155	166
Other equity investments	8	8
Contingent purchase consideration asset	64	84
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	59	4
Mutual funds	155	166
Other equity investments	0	0
Contingent purchase consideration asset	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
Contingent purchase consideration asset	0	0
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
Contingent purchase consideration asset	64	84
Cash and Cash Equivalents | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	530	55
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	530	55
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
Accounts Payable and Accrued Liabilities and Other Liabilities | Fair Value, Measurements, Recurring
Liabilities:
Contingent purchase consideration liability	233	225
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	$ 233	$ 225

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Revaluation Impact			$ (6)	$ (20)
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 239	$ 454	225	508
Net Additions	66	29	96	40
Payments	(65)	(10)	(78)	(45)
Revaluation Impact	(11)	9	(10)	20
Other	4	(3)	0	(2)
Balance at June 30,	233	196	233	196
Foreign Exchange Forward | Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Change in fair value of the FX contract	$ 0	$ (283)	$ 0	$ (325)

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) £ in Billions	Sep. 20, 2018GBP (£)	Jan. 31, 2019USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Jun. 30, 2020USD ($)	Jun. 30, 2019USD ($)	Mar. 31, 2019EUR (€)	Dec. 31, 2018USD ($)
Derivative [Line Items]
Total consideration					$ 737,000,000	$ 5,925,000,000
Increase in net investment hedges					$ 11,000,000
Senior Notes
Derivative [Line Items]
Debt instrument face amount		$ 5,000,000,000
Foreign Exchange Forward
Derivative [Line Items]
Loss on derivative			$ 11,000,000
Unrealized gain						$ 31,000,000
Treasury Lock
Derivative [Line Items]
Payments for derivative settlement		$ 122,000,000		$ 6,000,000
Jardine Lloyd Thompson Group plc
Derivative [Line Items]
Total consideration | £	£ 5.2
Jardine Lloyd Thompson Group plc | Senior Notes
Derivative [Line Items]
Debt instrument face amount | €							€ 1,100,000,000
Payments for derivative settlement				$ 7,300,000
Net investment hedge, threshold percentage of the equity balance					80.00%
Jardine Lloyd Thompson Group plc | Foreign Exchange Forward
Derivative [Line Items]
Derivative, loss on derivative			$ 26,000,000
Jardine Lloyd Thompson Group plc | Treasury Lock
Derivative [Line Items]
Derivative hedges, assets								$ 2,000,000,000

Leases - Narrative (Details)

Leases - Narrative (Details) $ in Millions	6 Months Ended
	Jun. 30, 2020USD ($)
Lessee, Lease, Description [Line Items]
Percentage of lease obligations used for office space	99.00%
Lessee, operating lease, lease not yet commenced, amount	$ 17
Lessee, operating lease, lease not yet commenced, term (years)	12 months
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

Leases - Lease Cost and Additio

Leases - Lease Cost and Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 97	$ 100	$ 189	$ 182
Short-term lease cost	1	2	2	3
Variable lease cost	27	39	64	76
Sublease income	(5)	(4)	(10)	(8)
Net lease cost	$ 120	$ 137	245	253
Operating cash outflows from operating leases			197	187
Right of use assets obtained in exchange for new operating lease liabilities			$ 129	$ 67
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	8 years 6 months 10 days	8 years 11 months 26 days	8 years 6 months 10 days	8 years 11 months 26 days
Weighted-average discount rate	3.05%	3.08%	3.05%	3.08%

Leases - Future Minimum Payment

Leases - Future Minimum Payments for Operating Leases (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Remainder of 2020	$ 208
2021	373
2022	348
2023	303
2024	259
2025	233
Subsequent years	822
Total future lease payments	2,546
Less: Imputed interest	(312)
Total	2,234
Current lease liabilities	332	$ 342
Long-term lease liabilities	$ 1,902	$ 1,926

Retirement Benefits (Narrative)

Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Pension, post-retirement and post-employment benefits	$ 2,197		$ 2,336
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	53
Estimated future employer contributions in current fiscal year	57
Jardine Lloyd Thompson Group plc
Defined Benefit Plan Disclosure [Line Items]
Pension, post-retirement and post-employment benefits			255
Pension, post-retirement and post-employment liabilities			1,003
Pension, post-retirement and post-employment plan assets			$ 748
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	73	$ 70
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Emploer contributions deferred	47
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 64	$ 46
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	61.00%
Equity Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	33.00%
Actual asset allocation percentage of equity	31.00%
Fixed Income Funds | United States
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	36.00%
Actual asset allocation percentage of equity	39.00%
Fixed Income Funds | United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	67.00%
Actual asset allocation percentage of equity	69.00%

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 9	$ 10	$ 17	$ 18
Interest cost	104	121	210	240
Expected return on plan assets	(207)	(217)	(417)	(430)
Amortization of prior service (credit) cost			0	0
Recognized actuarial loss	40	26	80	52
Net periodic benefit credit	(54)	(60)	(110)	(120)
Settlement loss			0	4
Total (credit) cost	(54)	(60)	(110)	(116)
Pension Benefits | United States
Defined Benefit Plan Disclosure [Line Items]
Interest cost	54	60	107	120
Expected return on plan assets	(87)	(85)	(173)	(171)
Recognized actuarial loss	18	11	36	22
Net periodic benefit credit	(15)	(14)	(30)	(29)
Pension Benefits | Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	9	10	17	18
Interest cost	50	61	103	120
Expected return on plan assets	(120)	(132)	(244)	(259)
Amortization of prior service (credit) cost			0	0
Recognized actuarial loss	22	15	44	30
Net periodic benefit credit	(39)	(46)	(80)	(91)
Settlement loss			0	4
Total (credit) cost			(80)	(87)
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	0	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	0	0
Net periodic benefit credit	0	0	0	0
Settlement loss			0	0
Total (credit) cost	0	0	0	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	0	0	0	0
Post-retirement Benefits | Foreign Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	0	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	0	0
Net periodic benefit credit	$ 0	$ 0	0	0
Settlement loss			0	0
Total (credit) cost			$ 0	$ 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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	$ (885)	$ (680)	$ (1,955)	$ (1,618)
Other net benefit (credits) cost	(63)	(70)	(127)	(134)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	9	10	17	18
Other net benefit (credits) cost	(63)	(70)	(127)	(134)
Total (credit) cost	(54)	(60)	(110)	(116)
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	0	0	0	0
Other net benefit (credits) cost	0	0	0	0
Total (credit) cost	$ 0	$ 0	$ 0	$ 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, 2020	Jun. 30, 2019
Pension Benefits
Weighted average assumptions:
Expected return on plan assets	5.31%	5.74%
Discount rate	2.57%	3.48%
Rate of compensation increase	1.76%	1.74%
Post-retirement Benefits
Weighted average assumptions:
Expected return on plan assets	0.00%	0.00%
Discount rate	2.72%	3.65%
Rate of compensation increase	0.00%	0.00%

Debt (Schedule Of Outstanding D

Debt (Schedule Of Outstanding Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Current portion of long-term debt	$ 716	$ 1,215
Short-term debt	1,216	1,215
Long-term debt	12,701	11,956
Long-term debt, net	11,985	10,741
Term Loan Facility
Debt Instrument [Line Items]
Term loan facility - one year	500	0
2.35% Senior Debt Obligations Due 2020
Debt Instrument [Line Items]
Long-term debt	$ 0	500
Interest rate	2.35%
3.50% Senior Debt Obligations Due 2020
Debt Instrument [Line Items]
Long-term debt	$ 699	698
Interest rate	3.50%
4.80% Senior Debt Obligations Due 2021
Debt Instrument [Line Items]
Long-term debt	$ 499	499
Interest rate	4.80%
Floating Rate Senior Debt Obligations Due 2021
Debt Instrument [Line Items]
Long-term debt	$ 299	298
2.75% Senior Debt Obligations Due 2022
Debt Instrument [Line Items]
Long-term debt	$ 499	498
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	597
Interest rate	3.50%
3.875% Senior Debt Obligations Due 2024
Debt Instrument [Line Items]
Long-term debt	$ 994	994
Interest rate	3.875%
3.50% Senior Debt Obligations Due 2025
Debt Instrument [Line Items]
Long-term debt	$ 497	497
Interest rate	3.50%
1.349% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 615	609
Interest rate	1.349%
3.75% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 597	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	$ 612	607
Interest rate	1.979%
2.250% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Long-term debt	$ 737	0
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	494
Interest rate	4.75%
4.35% Senior Debt Obligation Due 2047
Debt Instrument [Line Items]
Long-term debt	$ 493	492
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	$ 338	345
Interest rate	5.70%
$500 Million Two-Year Term Loan Facility
Debt Instrument [Line Items]
Long-term debt	$ 500	0
Other
Debt Instrument [Line Items]
Long-term debt	$ 5	$ 7

Debt (Narrative) (Details)

Debt (Narrative) (Details)

1 Months Ended

3 Months Ended

6 Months Ended

Mar. 31, 2020USD ($)

Jan. 31, 2020USD ($)

Sep. 30, 2019USD ($)

Jun. 30, 2019USD ($)

Apr. 30, 2019USD ($)

Mar. 31, 2019USD ($)

Jun. 30, 2019USD ($)

Jun. 30, 2020USD ($)

Jun. 30, 2019USD ($)

May 31, 2020USD ($)

Apr. 30, 2020USD ($)

Apr. 01, 2019USD ($)

Mar. 31, 2019EUR (€)

Jan. 31, 2019USD ($)

Debt Instrument [Line Items]

Commercial paper outstanding

$ 0

Payments for early extinguishment of debt

0

$ 585,000,000

April 2020 New Credit Facility

Debt Instrument [Line Items]

Debt facilities, maximum borrowing capacity

$ 0

$ 1,000,000,000

2.250% Senior Debt Obligations Due 2030

Debt Instrument [Line Items]

Interest rate

2.25%

1.349% Senior Debt Obligations Due 2026

Debt Instrument [Line Items]

Interest rate

1.349%

1.979% Senior Debt Obligations Due 2030

Debt Instrument [Line Items]

Interest rate

1.979%

Commercial Paper

Debt Instrument [Line Items]

Short-term debt

$ 1,500,000,000

Jardine Lloyd Thompson Group plc

Debt Instrument [Line Items]

Repayments of debt

$ 553,000,000

$ 450,000,000

Debt assumed in acquisition

$ 1,000,000,000

Payments for early extinguishment of debt

$ 32,000,000

Revolving Credit Facility | Amended Revolving Credit Facility

Debt Instrument [Line Items]

Debt facilities, maximum borrowing capacity

$ 1,800,000,000

Term of debt

5 years

Long-term line of credit

$ 1,000,000,000

$ 0

Term Loan Facility | $500 Million One-Year Term Loan and $500 Million Two-Year Term Loan

Debt Instrument [Line Items]

Long-term line 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

Term Loan Facility | $300 Million One-Year Term Loan Facility

Debt Instrument [Line Items]

Term of debt

1 year

Term Loan Facility | $300 Million Three-Year Term Loan Facility

Debt Instrument [Line Items]

Term of debt

3 years

Senior Notes

Debt Instrument [Line Items]

Repayments of debt

$ 500,000,000

$ 300,000,000

Debt instrument face amount

$ 5,000,000,000

Senior Notes | 2.250% Senior Debt Obligations Due 2030

Debt Instrument [Line Items]

Debt instrument face amount

$ 750,000,000

Interest rate

2.25%

Senior Notes | 1.349% Senior Debt Obligations Due 2026

Debt Instrument [Line Items]

Debt instrument face amount | €

€ 550,000,000

Interest rate

1.349%

1.349%

Senior Notes | 1.979% Senior Debt Obligations Due 2030

Debt Instrument [Line Items]

Debt instrument face amount | €

€ 550,000,000

Interest rate

1.979%

1.979%

Senior Notes | Senior Debt Obligations 4.375% Due 2029

Debt Instrument [Line Items]

Debt instrument face amount

$ 250,000,000

$ 1,500,000,000

1,250,000,000

Interest rate

4.375%

Senior Notes | Senior Debt Obligations 3.50% Due 2020

Debt Instrument [Line Items]

Debt instrument face amount

$ 700,000,000

Interest rate

3.50%

Senior Notes | Senior Debt Obligations 3.875% Due 2024

Debt Instrument [Line Items]

Debt instrument face amount

$ 1,000,000,000

Interest rate

3.875%

Senior Notes | Senior Debt Obligations 4.75% Due 2039

Debt Instrument [Line Items]

Debt instrument face amount

$ 500,000,000

Interest rate

4.75%

Senior Notes | Senior Debt Obligations 4.90% Due 2049

Debt Instrument [Line Items]

Debt instrument face amount

$ 1,250,000,000

Interest rate

4.90%

Senior Notes | Floating Rate Senior Notes Due 2021

Debt Instrument [Line Items]

Debt instrument face amount

$ 300,000,000

Senior Notes | Jardine Lloyd Thompson Group plc

Debt Instrument [Line Items]

Debt instrument face amount | €

€ 1,100,000,000

Debt (Estimated Fair Value of S

Debt (Estimated Fair Value of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 1,216	$ 1,215
Long-term debt	11,985	10,741
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	1,227	1,229
Long-term debt	$ 13,724	$ 11,953

Restructuring Costs - Narrative

Restructuring Costs - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Restructuring Cost and Reserve [Line Items]
Amounts accrued		$ 20	$ 112
ROU asset impairment loss	$ 11
Severance and consulting costs | Marsh Insurance Group
Restructuring Cost and Reserve [Line Items]
Amounts accrued		2
Severance and consulting costs | Mercer Consulting Group
Restructuring Cost and Reserve [Line Items]
Amounts accrued		6
Consulting costs and adjustments to restructuring liabilities for future rent under non-cancellable leases | Corporate
Restructuring Cost and Reserve [Line Items]
Amounts accrued		12
Jardine Lloyd Thompson Group plc
Restructuring Cost and Reserve [Line Items]
Amounts accrued		137	335
Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost	700	700
Restructuring and related cost, cost incurred to date	$ 137	137	$ 335
Amounts accrued		137
Jardine Lloyd Thompson Group plc | Acquisition related | Corporate
Restructuring Cost and Reserve [Line Items]
Amounts accrued		20
Jardine Lloyd Thompson Group plc | Acquisition related | Risk and Insurance Services Segment
Restructuring Cost and Reserve [Line Items]
Amounts accrued		100
Jardine Lloyd Thompson Group plc | Acquisition related | Consulting Segment
Restructuring Cost and Reserve [Line Items]
Amounts accrued		$ 17

Restructuring Costs (Restructur

Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 102	$ 112
Amounts Accrued	20	112
Cash Paid	(64)	(112)
Other	(1)	(10)
Liability at end of period	57	102
Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	51	73
Amounts Accrued	6	73
Cash Paid	(45)	(91)
Other	0	(4)
Liability at end of period	12	51
Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	51	39
Amounts Accrued	14	39
Cash Paid	(19)	(21)
Other	(1)	(6)
Liability at end of period	45	51
Jardine Lloyd Thompson Group plc
Restructuring Reserve [Roll Forward]
Liability at beginning of period	47	0
Amounts Accrued	137	335
Cash Paid	(127)	(265)
Non-cash charges	(24)	(23)
Liability at end of period	33	47
Jardine Lloyd Thompson Group plc | Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	42	0
Amounts Accrued	29	154
Cash Paid	(56)	(112)
Non-cash charges	0	0
Liability at end of period	15	42
Jardine Lloyd Thompson Group plc | Real estate related costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	5	0
Amounts Accrued	31	38
Cash Paid	(4)	(14)
Non-cash charges	(21)	(19)
Liability at end of period	11	5
Jardine Lloyd Thompson Group plc | Information Technology
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0	0
Amounts Accrued	37	45
Cash Paid	(34)	(45)
Non-cash charges	(3)	0
Liability at end of period	0	0
Jardine Lloyd Thompson Group plc | Consulting and other outside services
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0	0
Amounts Accrued	40	98
Cash Paid	(33)	(94)
Non-cash charges	0	(4)
Liability at end of period	$ 7	$ 0

Common Stock (Details)

Common Stock (Details) - USD ($)	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Nov. 30, 2019
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)		1,000,000
Payments for repurchase of common stock	$ 0	$ 100,000,000
Stock-based compensation, shares issued during period (in shares)	2,800,000	3,800,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	0
Share repurchases program, authorized amount (up to)			$ 2,500,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 2,400,000,000

Claims, Lawsuits And Other Co_2

Claims, Lawsuits And Other Contingencies (Details) $ in Millions	Jun. 30, 2020USD ($)	Jun. 30, 2020GBP (£)	Feb. 28, 2019USD ($)	Feb. 28, 2019GBP (£)
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss	$ 83	£ 68,000,000
Other Contingencies-Guarantees
Loss Contingencies [Line Items]
Amount reinsured by third party (up to)		£ 40,000,000
Jardine Lloyd Thompson Group plc
Loss Contingencies [Line Items]
Loss contingency accrual			$ 77	£ 59,000,000

Segment Information - Narrative

Segment Information - Narrative (Details)	Mar. 31, 2019countrysegment	Jun. 30, 2020country
Segment Reporting Information [Line Items]
Number of countries in which entity operates		130
Jardine Lloyd Thompson Group plc
Segment Reporting Information [Line Items]
Number of business segments (segment) | segment	3
Number of countries in which entity operates	41

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, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 4,189	$ 4,349	$ 8,840	$ 8,420
Operating Income (Loss)	885	680	1,955	1,618
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,603	2,574	5,514	4,997
Interest on fiduciary funds	9	26	32	49
Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,616	1,800	3,378	3,473
Operating Segments
Segment Reporting Information [Line Items]
Revenue	4,219	4,374	8,892	8,470
Operating Income (Loss)	951	795	2,087	1,807
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,603	2,574	5,514	4,997
Operating Income (Loss)	696	517	1,550	1,250
Interest on fiduciary funds	9	26	32	49
Equity method income	14	4	13	6
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,616	1,800	3,378	3,473
Operating Income (Loss)	255	278	537	557
Interest on fiduciary funds	1	1	1	2
Equity method income		5	4	10
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	(30)	(25)	(52)	(50)
Operating Income (Loss)	(66)	(115)	(132)	(189)
Intersegment Eliminations | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	4	3	5	4
Intersegment Eliminations | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	$ 26	$ 22	$ 47	$ 46

Segment Information (Details of

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting Information [Line Items]
Revenue	$ 4,189	$ 4,349	$ 8,840	$ 8,420
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,603	2,574	5,514	4,997
Risk and Insurance Services Segment | Marsh Insurance Group
Segment Reporting Information [Line Items]
Revenue	2,161	2,156	4,222	3,893
Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group
Segment Reporting Information [Line Items]
Revenue	433	392	1,260	1,055
Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,616	1,800	3,378	3,473
Consulting Segment | Mercer Consulting Group
Segment Reporting Information [Line Items]
Revenue	1,149	1,260	2,400	2,415
Consulting Segment | Oliver Wyman Group Consulting Group
Segment Reporting Information [Line Items]
Revenue	467	540	978	1,058
Operating Segments
Segment Reporting Information [Line Items]
Revenue	4,219	4,374	8,892	8,470
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,603	2,574	5,514	4,997
Operating Segments | Risk and Insurance Services Segment | Marsh Insurance Group
Segment Reporting Information [Line Items]
Revenue	2,168	2,174	4,244	3,927
Operating Segments | Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group
Segment Reporting Information [Line Items]
Revenue	435	400	1,270	1,070
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,616	1,800	3,378	3,473
Operating Segments | Consulting Segment | Mercer Consulting Group
Segment Reporting Information [Line Items]
Revenue	1,149	1,260	2,400	2,415
Operating Segments | Consulting Segment | Oliver Wyman Group Consulting Group
Segment Reporting Information [Line Items]
Revenue	467	540	978	1,058
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (30)	$ (25)	$ (52)	$ (50)

New Accounting Guidance - Narra

New Accounting Guidance - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Jun. 30, 2020	Jan. 01, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201602Member
Operating lease, liability		$ 2,234
Operating lease, right-of-use asset	$ 1,921	$ 1,882
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability			$ 1,900
Operating lease, right-of-use asset			1,700
Other liabilities			$ 200