Marsh & McLennan Companies (MMC) 10-Q 30 Oct 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 25, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
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
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		504,668,238
Entity Central Index Key	0000062709
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false

Consolidated Statements of Inco

Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 3,968	$ 3,504	$ 12,388	$ 11,238
Expense:
Compensation and benefits	2,437	2,083	7,256	6,442
Other operating expenses	1,064	880	3,047	2,656
Operating expenses	3,501	2,963	10,303	9,098
Operating income	467	541	2,085	2,140
Other net benefit credits	69	63	203	194
Interest income	4	2	34	8
Interest expense	(133)	(69)	(394)	(198)
Cost of extinguishment of debt	0	0	(32)	0
Investment income (loss)	7	(52)	20	(24)
Acquisition related derivative contracts	0	(100)	(8)	(100)
Income before income taxes	414	385	1,908	2,020
Income tax expense	108	106	531	509
Net income before non-controlling interests	306	279	1,377	1,511
Less: Net income attributable to non-controlling interests	3	3	26	14
Net income attributable to the Company	$ 303	$ 276	$ 1,351	$ 1,497
Net income per share attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 0.60	$ 0.55	$ 2.67	$ 2.96
Diluted net income per share attributable to the Company (usd per share)	$ 0.59	$ 0.54	$ 2.64	$ 2.93
Average number of shares outstanding:
Average number of shares outstanding - Basic (in shares)	506	504	506	506
Average number of shares outstanding - Diluted (in shares)	511	510	511	512
Shares outstanding (in shares)	505	504	505	504

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Statement of Comprehensive Income [Abstract]
Net income before non-controlling interests	$ 306	$ 279	$ 1,377	$ 1,511
Other comprehensive (loss) income, before tax:
Foreign currency translation adjustments	(475)	(237)	(366)	(538)
Gain related to pension/post-retirement plans	82	23	102	131
Other comprehensive (loss), before tax	(393)	(214)	(264)	(407)
Income tax on other comprehensive loss	11	9	20	24
Other comprehensive income (loss), net of tax	(404)	(223)	(284)	(431)
Comprehensive (loss) income	(98)	56	1,093	1,080
Less: comprehensive income attributable to non-controlling interest	3	3	26	14
Comprehensive (loss) income attributable to the Company	$ (101)	$ 53	$ 1,067	$ 1,066

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 1,213	$ 1,066
Receivables
Commissions and fees	4,636	3,984
Advanced premiums and claims	126	79
Other	575	366
Gross receivables	5,337	4,429
Less-allowance for doubtful accounts and cancellations	(139)	(112)
Net receivables	5,198	4,317
Other current assets	645	551
Total current assets	7,056	5,934
Goodwill	14,286	9,599
Other intangible assets	2,869	1,437
Fixed assets (net of accumulated depreciation and amortization of $1,944 at September 30, 2019 and $1,842 at December 31, 2018)	816	701
Pension related assets	1,857	1,688
Right of use assets	1,957	0
Deferred tax assets	603	680
Other assets	1,653	1,539
Total assets	31,097	21,578
Current liabilities:
Short-term debt	1,139	314
Accounts payable and accrued liabilities	2,479	2,234
Accrued compensation and employee benefits	1,762	1,778
Acquisition related derivatives	0	441
Current lease liabilities	341	0
Accrued income taxes	251	157
Dividends payable	232	0
Total current liabilities	6,204	4,924
Fiduciary liabilities	7,547	5,001
Less – cash and investments held in a fiduciary capacity	(7,547)	(5,001)
Net fiduciary assets	0	0
Long-term debt	11,429	5,510
Pension, post-retirement and post-employment benefits	1,998	1,911
Long-term lease liabilities	1,957	0
Liabilities for errors and omissions	324	287
Other liabilities	1,388	1,362
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, 2019 and December 31, 2018	561	561
Additional paid-in capital	796	817
Retained earnings	14,811	14,347
Accumulated other comprehensive loss	(4,931)	(4,647)
Non-controlling interests	177	73
Stockholders' equity before treasury stock	11,414	11,151
Less – treasury shares, at cost, 55,643,998 shares at September 30, 2019 and 56,804,468 shares at December 31, 2018	(3,617)	(3,567)
Total equity	7,797	7,584
Total liabilities and stockholders' equity	$ 31,097	$ 21,578

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Fixed assets, accumulated depreciation and amortization	$ 1,944	$ 1,842
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	55,643,998	56,804,468

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Operating cash flows:
Net income before non-controlling interests	$ 1,377	$ 1,511
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization of fixed assets and capitalized software	245	236
Amortization of intangible assets	235	135
Non cash lease expense	236	0
Adjustments and payments related to contingent consideration liability	(9)	(10)
Charge for early extinguishment of debt	32	0
Provision for deferred income taxes	95	66
Loss (gain) on investments	(20)	24
Loss (gain) on disposition of assets	36	(53)
Share-based compensation expense	184	146
Change in fair value of acquisition-related derivative contracts	8	100
Changes in assets and liabilities:
Net receivables	(84)	(210)
Other current assets	30	19
Other assets	(59)	(51)
Accounts payable and accrued liabilities	(126)	(3)
Accrued compensation and employee benefits	(281)	(312)
Accrued income taxes	120	(13)
Contributions to pension and other benefit plans in excess of current year expense/credit	(269)	(250)
Other liabilities	(149)	11
Operating lease liabilities	(240)	0
Effect of exchange rate changes	(70)	(27)
Net cash provided by operations	1,291	1,319
Financing cash flows:
Purchase of treasury shares	(300)	(675)
Net increase in commercial paper	325	75
Net increase in short term borrowings	300	0
Proceeds from issuance of debt	6,459	592
Repayments of debt	(760)	(10)
Payment of bridge loan fees	0	(24)
Payments for early extinguishment of debt	(585)	0
Purchase of non-controlling interests	(75)	0
Acquisition-related derivative payments	(337)	0
Shares withheld for taxes on vested units – treasury shares	(89)	(62)
Issuance of common stock from treasury shares	132	72
Payments of deferred and contingent consideration for acquisitions	(60)	(106)
Distributions of non-controlling interests	(18)	(15)
Dividends paid	(655)	(594)
Net cash provided by (used for) financing activities	4,337	(747)
Investing cash flows:
Capital expenditures	(284)	(222)
Sales (purchases) of long-term investments	193	(1)
Purchase of equity investment	(91)	0
Proceeds from sales of fixed assets	4	3
Dispositions	225	5
Acquisitions	(5,500)	(536)
Other, net	(51)	(1)
Net cash used for investing activities	(5,504)	(752)
Effect of exchange rate changes on cash and cash equivalents	23	(74)
Increase (decrease) in cash and cash equivalents	147	(254)
Cash and cash equivalents at beginning of period	1,066	1,205
Cash and cash equivalents at end of period	$ 1,213	$ 951

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 year at Dec. 31, 2017		$ 561	$ 784	$ 13,140	$ (4,043)	$ (3,083)	$ 83
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			20
Issuance of shares under stock compensation plans and employee stock purchase plans			(33)			171
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2014-09				364
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2016-01					(14)
Net income attributable to the Company	$ 1,511			1,497			14
Dividend equivalents declared				(5)
Dividends declared				(800)
Other comprehensive loss, net of tax	(431)				(431)
Purchase of treasury shares						(675)
Net non-controlling interests (disposed) acquired							0
Distributions and other changes							(12)
Balance, end of period at Sep. 30, 2018	$ 7,538		771	14,196	(4,488)	(3,587)	85
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 1.580
Balance, beginning of year at Jun. 30, 2018		561	732	14,131	(4,265)	(3,443)	81
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			46
Issuance of shares under stock compensation plans and employee stock purchase plans			(7)			31
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2014-09				0
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2016-01					0
Net income attributable to the Company	$ 279			276			3
Dividend equivalents declared				(2)
Dividends declared				(209)
Other comprehensive loss, net of tax	(223)				(223)
Purchase of treasury shares						(175)
Net non-controlling interests (disposed) acquired							0
Distributions and other changes							1
Balance, end of period at Sep. 30, 2018	$ 7,538		771	14,196	(4,488)	(3,587)	85
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0.415
Balance, beginning of year at Dec. 31, 2018	$ 7,584	561	817	14,347	(4,647)	(3,567)	73
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			65
Issuance of shares under stock compensation plans and employee stock purchase plans			(5)			29
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2014-09				0
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2016-01					0
Net income attributable to the Company	1,377			1,351			3
Dividend equivalents declared				(2)
Dividends declared				(231)
Other comprehensive loss, net of tax	(284)				(284)
Purchase of treasury shares						(200)
Net non-controlling interests (disposed) acquired							(100)
Distributions and other changes							2
Balance, end of period at Sep. 30, 2019	$ 7,797		796	14,811	(4,931)	(3,617)	177
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 1.740
Balance, beginning of year at Jun. 30, 2019		$ 561	736	14,741	(4,527)	(3,446)	272
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			23
Issuance of shares under stock compensation plans and employee stock purchase plans			(44)			250
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2014-09				0
Cumulative effect of adoption of new accounting standards | Accounting Standards Update 2016-01					0
Net income attributable to the Company	$ 306			303			26
Dividend equivalents declared				(6)
Dividends declared				(881)
Other comprehensive loss, net of tax	(404)				(404)
Purchase of treasury shares						(300)
Net non-controlling interests (disposed) acquired							95
Distributions and other changes							(17)
Balance, end of period at Sep. 30, 2019	$ 7,797		$ 796	$ 14,811	$ (4,931)	$ (3,617)	$ 177
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share (in dollars per share)	$ 0.455

Nature of Operations

Nature of Operations	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Nature of Operations	Nature of Operations Marsh & McLennan Companies, Inc. and its consolidated subsidiaries (the "Company"), a global professional services firm, is organized based on the different services that it offers. Under this structure, the Company’s two segments are Risk and Insurance Services and Consulting. The Risk and Insurance Services ("RIS") segment provides risk management solutions, services, advice and insurance broking, reinsurance broking and insurance program management services for businesses, public entities, insurance companies, associations, professional services organizations, and private clients. The Company conducts business in this segment through Marsh and Guy Carpenter. The Company conducts business in its Consulting segment through Mercer and Oliver Wyman. Mercer provides consulting expertise, advice, services and solutions in the areas of health, wealth and career consulting services and products. Oliver Wyman provides specialized management and economic and brand consulting services. On April 1, 2019, the Company completed its previously announced 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 operation for the three month period ended September 30, 2019 are included in the Company's results of operations for the three month period ended September 30, 2019 . JLT's results of operation for the six months from April 1, 2019 to September 30, 2019 are included in the Company's results of operations for the nine month period ended September 30, 2019 . Prior periods in 2018 do not reflect JLT’s results of operations and therefore may affect comparability. 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 is included in Mercer Health and Wealth.

Principles of Consolidation and

Principles of Consolidation and Other Matters	9 Months Ended
	Sep. 30, 2019
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, 2018 (the " 2018 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 nine month periods ended September 30, 2019 and 2018 . 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 September 30, 2019 , the Company maintained $193 million compared to $186 million at December 31, 2018 related to these regulatory requirements. Investments The caption "Investment income" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds. The Company holds investments in certain private equity funds 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 income of $7 million and $20 million for the three and nine month periods ended September 30, 2019 compared to net investment losses of $52 million and $24 million for the three and nine month periods ended September 30, 2018 . The three and nine month periods ending September 30, 2019 includes gains of $4 million and $10 million related to mark-to-market changes in equity securities and gains of $3 million and $10 million related to investments in private equity funds and other investments. The three and nine months periods ending September 30, 2018 include an $81 million impairment charge related to an other than temporary decline in the Company's equity method investment in Alexander Forbes (see Note 10). The three and nine month periods ending September 30, 2018 also include gains of $25 million and $43 million , respectively, related to mark-to-market changes in equity securities and $4 million and $14 million , respectively, related to investments in private equity funds and other investments. Leases Effective January 1, 2019, the Company adopted the new accounting standard related to leases. Under the new standard, a lessee is required to recognize assets and liabilities for its leases with lease terms of more than 12 months. The Company adopted this new standard using the modified retrospective method, which applies the new guidance beginning with the year of adoption, with the cumulative effect of initially applying the standard recognized as an adjustment to retained earnings at January 1, 2019. There was no cumulative-effect adjustment required to be recorded to retained earnings upon transition. Prior period results have not been restated to reflect the adoption of this new standard. On January 1, 2019, the Company recognized a lease liability of $1.9 billion and a corresponding right-of-use asset ("ROU asset") of $1.7 billion , including the reclassification of approximately $200 million of unamortized lease incentives and restructuring liabilities, upon the adoption of this standard, with minimal impact on the consolidated statement of income. See Note 12 for further information related to Leases. Income Taxes The Company's effective tax rate in the third quarter of 2019 was 26.0% compared with 27.5% in the third quarter of 2018 . The effective tax rates for the first nine months of 2019 and 2018 were 27.8% and 25.2% , respectively. The rate in the first nine 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 Transaction. The rate in the third quarter of 2018 as well as the first nine months of 2018 reflect the impact of a charge related to the Company’s investment in Alexander Forbes as discussed in Note 10, largely offset by favorable adjustments to the estimated impact of tax reform. Both periods reflect the effect of other 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 is routinely examined by tax authorities in the jurisdictions in which it has significant operations. The Company regularly considers the likelihood of assessments in each of the taxing jurisdictions resulting from examinations. When evaluating the potential imposition of penalties, the Company considers a number of relevant factors under penalty statutes, including appropriate disclosure of the tax return position, the existence of legal authority supporting the Company's position, and reliance on the opinion of professional tax advisors. 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 $78 million at December 31, 2018 to $76 million at September 30, 2019 due to settlements of audits and expirations of statutes of limitation partially offset by current accruals. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $7 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 their 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	9 Months Ended
	Sep. 30, 2019
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. Other revenue included in the consolidated statements of income that is not from contracts with customers is less than 1% of total revenue, and therefore is not presented as a separate line item. Risk and Insurance Services Risk and Insurance Services revenue reflects compensation for brokerage and consulting services through commissions and fees. Commission rates and fees vary in amount and can depend upon a number of factors, including the type of insurance or reinsurance coverage provided, the particular insurer or reinsurer selected, and the capacity in which the broker acts and negotiates with clients. For the majority of the insurance and reinsurance brokerage arrangements, advice and services provided which culminate in the placement of an effective policy are considered a single performance obligation. Arrangements with clients may include the placement of a single policy, multiple policies or a combination of policy placements and other services. Consideration related to such "bundled arrangements" is allocated to the individual performance obligations based on their relative fair value. Revenue for policy placement is generally recognized on the policy effective date, at which point control over the services provided by the Company has transferred to the client and the client has accepted the services. The contractual terms for certain fee based brokerage arrangements meet the criteria for revenue recognition over time. For such arrangements, revenue is recognized using output measures, which correspond to the progress toward completing the performance obligation. Fees for non-risk transfer services provided to clients are recognized over time in the period the services are provided, using a proportional performance model, primarily based on input measures. These measures of progress provide a faithful depiction of the progress towards completion of the performance obligation. Revenue related to reinsurance brokerage for excess of loss ("XOL") treaties is estimated based on contractually specified minimum or deposit premiums, and adjusted as additional evidence of the ultimate amount of brokerage is received. Revenue for quota share treaties is estimated based on indications of estimated premium income provided by the ceding insurer. The estimated brokerage revenue recognized for quota share treaties is constrained to an amount that is probable to not have a significant negative adjustment. The estimated revenue and the constraint are evaluated as additional evidence of the ultimate amount of underlying risks to be covered is received over the 12 to 18 months following the effective date of the placement. In addition to commissions and fees from its clients, the Company also receives other compensation from insurance companies. This other insurer compensation includes, among other things, payments for consulting and analytics services provided to insurers, fees for administrative and other services provided to or on behalf of insurers (including services relating to the administration and management of quota shares, panels and other facilities in which insurers participate). The Company is also eligible for certain contingent commissions from insurers based on the attainment of specified metrics (i.e., volume and loss ratio measures) relating to Marsh's placements, particularly in Marsh & McLennan Agency ("MMA") and in parts of Marsh's international operations. Revenue for contingent commissions from insurers is estimated based on historical evidence of the achievement of the respective contingent metrics and recorded as the underlying policies that contribute to the achievement of the metric are placed. Due to the uncertainty of the amount of contingent consideration that will be received, the estimated revenue is constrained to an amount that is probable to not have a significant negative adjustment. Contingent consideration is generally received in the first quarter of the subsequent year. A significant majority of the Company's Risk and Insurance Services revenue is for performance obligations recognized at a point in time. Marsh and Guy Carpenter also receive interest income on certain funds (such as premiums and claims proceeds) held in a fiduciary capacity for others. Insurance brokerage commissions are generally invoiced on the policy effective date. Fee based arrangements generally include a percentage of the total fee due upon signing the arrangement, with additional fixed installments payable over the remainder of the year. Payment terms range from receipt of invoice up to 30 days from invoice date. Reinsurance brokerage revenue is recognized on the effective date of the treaty. Payment terms depend on the type of reinsurance. For XOL treaties, brokerage revenue is typically collected in four installments during an annual treaty period based on a contractually specified minimum or deposit premium. For proportional or quota share treaties, brokerage is billed as underlying insured risks attach to the reinsurance treaty, generally over 12 to 18 months. Consulting The major component of revenue in the Consulting business is fees paid by clients for advice and services. Mercer, principally through its health line of business, also receives revenue in the form of commissions received from insurance companies for the placement of group (and occasionally individual) insurance contracts, primarily health, life and accident coverages. Revenue for Mercer’s investment management business and certain of Mercer’s defined benefit administration services consists principally of fees based on assets under delegated management or administration. Consulting projects in Mercer’s wealth and career businesses, as well as consulting projects in Oliver Wyman typically consist of a single performance obligation, which is recognized over time as control is transferred continuously to customers. Typically, revenue is recognized over time using an input measure of time expended to date relative to total estimated time incurred at project completion. Incurred hours represent services rendered and thereby faithfully depicts the transfer of control to the customer. On a limited number of engagements, performance fees may also be earned for achieving certain prescribed performance criteria. Revenue for achievement is estimated and constrained to an amount that is probable to not have a significant negative adjustment. A significant majority of fee revenues in the Consulting segment is recognized over time. For consulting projects, Mercer generally invoices monthly in arrears with payment due within 30 days of the invoice date. Fees for delegated management services are either deducted from the net asset value of the fund or invoiced to the client on a monthly or quarterly basis in arrears. Oliver Wyman typically bills its clients 30 - 60 days in arrears with payment due upon receipt of the invoice. Health brokerage and consulting services are components of both Marsh, which includes MMA, and Mercer, with approximately 63% of such revenues reported in Mercer. Health contracts typically involve a series of distinct services that are treated as a single performance obligation. Revenue for these services is recognized over time based on the amount of remuneration the Company expects to be entitled in exchange for these services. Payments for health brokerage and consulting services are typically paid monthly in arrears from carriers based on insured lives under the contract. The following schedule disaggregates components of the Company's revenue: Three Months Ended September 30, Nine Months Ended (In millions) 2019 2019 Marsh: EMEA $ 536 $ 1,821 Asia Pacific 242 698 Latin America 110 304 Total International 888 2,823 U.S./Canada 1,014 2,972 Total Marsh 1,902 5,795 Guy Carpenter 273 1,328 Subtotal 2,175 7,123 Fiduciary interest income 31 80 Total Risk and Insurance Services $ 2,206 $ 7,203 Mercer: Wealth $ 592 $ 1,748 Health 441 1,341 Career 247 606 Total Mercer 1,280 3,695 Oliver Wyman 505 1,563 Total Consulting $ 1,785 $ 5,258 The following schedule provides contract assets and contract liabilities information from contracts with customers. (In millions) September 30, 2019 January 1, 2019 Contract Assets $ 240 $ 112 Contract Liabilities $ 611 $ 545 The Company records accounts receivable when the right to consideration is unconditional, subject only to the passage of time. Contract assets primarily relate to quota share reinsurance brokerage and contingent insurer revenue. The Company does not have the right to bill and collect revenue for quota share brokerage until the underlying policies written by the ceding insurer attach to the treaty. Estimated revenue related to achievement of volume or loss ratio metrics cannot be billed or collected until all related policy placements are completed and the contingency is resolved. The change in contract assets from January 1, 2019 to September 30, 2019 is primarily due to the addition of $58 million from JLT and $353 million of additions during the period, partly offset by $262 million transferred to accounts receivables, as the rights to bill and collect became unconditional. 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. The change in contract liabilities includes cash received for performance obligations not yet fulfilled of $400 million and $45 million related to JLT's opening balance offset by revenue recognized in the first nine months of 2019 that was included in the contract liability balance, at the beginning of the year of $378 million . The amount of revenue recognized in the first nine months of 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 , which includes a $17 million adjustment of previous estimates related to a multi-year Guy Carpenter contract in the third quarter of 2019. 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 $33 million for Marsh, $127 million for Mercer and $2 million for Oliver Wyman. The Company expects revenue in 2020, 2021, 2022, 2023 and 2024 and beyond of $107 million , $41 million , $10 million , $1 million and $3 million , respectively, related to these performance obligations.

Fiduciary Assets and Liabilitie

Fiduciary Assets and Liabilities	9 Months Ended
	Sep. 30, 2019
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 $31 million and $80 million for the three and nine month periods ended September 30, 2019 , respectively, and $18 million and $46 million for the three and nine month periods ending September 30, 2018 , respectively. The Consulting segment recorded fiduciary interest income of less than $1 million and $2 million for the three and nine month periods ended September 30, 2019 , respectively, as compared to $1 million and $3 million for the same periods in 2018. 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 $9.6 billion at September 30, 2019 and $7.3 billion at December 31, 2018 . 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	9 Months Ended
	Sep. 30, 2019
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 September 30, Nine Months Ended (In millions, except per share amounts) 2019 2018 2019 2018 Net income before non-controlling interests $ 306 $ 279 $ 1,377 $ 1,511 Less: Net income attributable to non-controlling interests 3 3 26 14 Net income attributable to the Company $ 303 $ 276 $ 1,351 $ 1,497 Basic weighted average common shares outstanding 506 504 506 506 Dilutive effect of potentially issuable common shares 5 6 5 6 Diluted weighted average common shares outstanding 511 510 511 512 Average stock price used to calculate common stock equivalents $ 99.97 $ 84.68 $ 94.75 $ 83.05

Supplemental Disclosures to the

Supplemental Disclosures to the Consolidated Statements of Cash Flows	9 Months Ended
	Sep. 30, 2019
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 nine -month periods ended September 30, 2019 and 2018 . (In millions) 2019 2018 Assets acquired, excluding cash $ 8,619 $ 679 Liabilities assumed (2,758 ) (35 ) Non-controlling interests assumed (295 ) — Contingent/deferred purchase consideration (66 ) (108 ) Net cash outflow for current year acquisitions $ 5,500 $ 536 (In millions) 2019 2018 Interest paid $ 387 $ 225 Income taxes paid, net of refunds $ 442 $ 455 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 $60 million for the nine months ended September 30, 2019 . This consisted of deferred purchase consideration related to prior years' acquisitions of $37 million and contingent consideration of $23 million . For the nine months ended September 30, 2018 , the Company paid deferred and contingent consideration of $106 million , consisting of deferred purchase consideration related to prior years' acquisitions of $59 million and contingent consideration of $47 million . The following amounts are included in the operating section of the consolidated statements of cash flows. For the nine months ended September 30, 2019 , the Company recorded an expense for adjustments to contingent consideration liabilities of $26 million and made contingent consideration payments of $35 million . For the nine months ended September 30, 2018 , the Company recorded an expense for adjustments to contingent consideration liabilities of $19 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 $164 million and $129 million for the nine months ended September 30, 2019 and 2018 , respectively. The Company recorded stock-based compensation expense for equity awards related to restricted stock units, performance stock units and stock options of $184 million and $146 million for the nine -month periods ended September 30, 2019 and 2018 , respectively. Effective January 1, 2019, the Company adopted the new accounting guidance related to leases, which requires a lessee to recognize assets and liabilities for its leases. Upon adoption of this accounting standard, the Company recorded a non cash Right-of-Use Asset ("ROU asset") of $1.7 billion and lease liability of $1.9 billion

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	9 Months Ended
	Sep. 30, 2019
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 nine -month periods ended September 30, 2019 and 2018 , including amounts reclassified out of AOCI, are as follows: (In millions) Unrealized Investment Gains (Losses) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of July 1, 2019 $ — $ (2,942 ) $ (1,585 ) $ (4,527 ) Other comprehensive income before reclassifications — 56 (475 ) (419 ) Amounts reclassified from accumulated other comprehensive income — 15 — 15 Net current period other comprehensive income (loss) — 71 (475 ) (404 ) Balance as of September 30, 2019 $ — $ (2,871 ) $ (2,060 ) $ (4,931 ) (In millions) Unrealized Investment Gains (Losses) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of July 1, 2018 $ — $ (2,807 ) $ (1,458 ) $ (4,265 ) Other comprehensive income (loss) before reclassifications — (13 ) (242 ) (255 ) Amounts reclassified from accumulated other comprehensive income — 32 — 32 Net current period other comprehensive income (loss) — 19 (242 ) (223 ) Balance as of September 30, 2018 $ — $ (2,788 ) $ (1,700 ) $ (4,488 ) (In millions) Unrealized Investment Gains (Losses) 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 (loss) income before reclassifications — 26 (366 ) (340 ) Amounts reclassified from accumulated other comprehensive income — 56 — 56 Net current period other comprehensive income (loss) — 82 (366 ) (284 ) Balance as of September 30, 2019 $ — $ (2,871 ) $ (2,060 ) $ (4,931 ) (In millions) Unrealized Investment Gains (Losses) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2017 $ 14 $ (2,892 ) $ (1,165 ) $ (4,043 ) Cumulative effect of amended accounting standard (14 ) — — (14 ) Other comprehensive income (loss) before reclassifications — 16 (535 ) (519 ) Amounts reclassified from accumulated other comprehensive income — 88 — 88 Net current period other comprehensive income (loss) — 104 (535 ) (431 ) Balance as of September 30, 2018 $ — $ (2,788 ) $ (1,700 ) $ (4,488 ) The components of other comprehensive income (loss) for the three and nine -month periods ended September 30, 2019 and 2018 are as follows: Three Months Ended September 30, 2019 2018 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (475 ) $ — $ (475 ) $ (237 ) $ 5 $ (242 ) 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) 25 6 19 36 7 29 Effect of remeasurement (a) (8 ) (2 ) (6 ) 3 — 3 Effect of settlement (a) 2 — 2 — — — Subtotal 18 3 15 38 6 32 Foreign currency translation adjustments 64 8 56 (15 ) (2 ) (13 ) Pension/post-retirement plans gains 82 11 71 23 4 19 Other comprehensive (loss) income $ (393 ) $ 11 $ (404 ) $ (214 ) $ 9 $ (223 ) (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. Nine Months Ended September 30, 2019 2018 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (366 ) $ — $ (366 ) $ (538 ) $ (3 ) $ (535 ) Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (2 ) (1 ) (1 ) (3 ) (1 ) (2 ) Net actuarial losses (a) 77 18 59 110 23 87 Effect of remeasurement (a) (9 ) (2 ) (7 ) 3 — 3 Effect of settlement (a) 6 1 5 — — — Subtotal 72 16 56 110 22 88 Foreign currency translation adjustments 30 4 26 21 5 16 Pension/post-retirement plans gains 102 20 82 131 27 104 Other comprehensive (loss) income $ (264 ) $ 20 $ (284 ) $ (407 ) $ 24 $ (431 ) (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	9 Months Ended
	Sep. 30, 2019
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. On April 1, 2019, the Company completed the JLT Transaction to purchase 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 ), and the Company 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 Company believes the Transaction strengthens MMC’s leadership position in insurance and reinsurance broking, health and retirement. The addition of over 10,000 colleagues provides deeper industry expertise in almost every part of the Company. The Transaction also builds on MMC’s efforts to expand in faster-growing geographies and market segments, and facilitates investment in data and analytics. The Risk and Insurance Services segment completed four acquisitions during the first nine months of 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. Total purchase consideration for acquisitions made during the nine months ended September 30, 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 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 $37 million of deferred purchase consideration and $58 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 2019 based on the estimated fair values for JLT and other acquisitions as of their respective acquisition dates: Acquisitions through September 30, 2019 (In millions) JLT Other Total Acquisitions Cash $ 5,568 $ 291 $ 5,859 Estimated fair value of deferred/contingent consideration — 66 66 Total consideration $ 5,568 $ 357 $ 5,925 Allocation of purchase price: Cash and cash equivalents $ 353 $ 6 $ 359 Accounts receivable, net 714 5 719 Other current assets 143 — 143 Fixed assets, net 89 2 91 Other intangible assets 1,613 143 1,756 Goodwill 4,761 201 4,962 Right of use assets 382 — 382 Deferred tax assets 65 — 65 Other assets 493 8 501 Total assets acquired 8,613 365 8,978 Current liabilities 689 5 694 Fiduciary liabilities 1,275 — 1,275 Less - fiduciary assets (1,275 ) — (1,275 ) Long-term debt 1,044 — 1,044 Long-term lease liability 389 — 389 Pension, post-retirement and post-employment liabilities 248 — 248 Liabilities for errors and omissions 31 — 31 Other liabilities 349 3 352 Total liabilities assumed 2,750 8 2,758 Non controlling interests 295 — 295 Net assets acquired $ 5,568 $ 357 $ 5,925 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 instrument 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. During the third quarter of 2019, the Company made certain adjustments to the above JLT purchase price allocation, which included a reduction of identified intangible assets of approximately $50 million , adjustment of related deferred taxes, and an increase in goodwill of approximately $65 million . The third quarter of 2019 included a credit of $4 million to adjust previously expensed amortization based on the current purchase price allocation. Items subject to change include the following: • Amounts of intangible assets, fixed assets, capitalized software assets and right-of-use assets, subject to finalization of valuation efforts; • Amounts for contingencies, pending the finalization of the Company’s assessment of the portfolio of contingencies; • Amounts for income tax assets, receivables and liabilities, pending the filing of the acquired companies' pre-acquisition income tax returns and receipt of information from taxing authorities which may change certain estimates and assumptions used; and • Amounts for deferred tax assets and liabilities pending the finalization of valuations of the assets acquired, liabilities assumed and associated goodwill. 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 2019 : Intangible assets through September 30, 2019 (In millions) JLT Other Total JLT Weighted Average Amortization Period Other Weighted Average Amortization Period Client relationships $ 1,511 $ 136 $ 1,647 13 years 12 years Other 102 7 109 4 years 3 years $ 1,613 $ 143 $ 1,756 During the second and third quarters of 2019, the Company purchased the outstanding non-controlling interests of several JLT subsidiaries for cash payments of approximately $75 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. 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. Prior-Year Acquisitions The Risk and Insurance Services segment completed twelve acquisitions during 2018 . • February – MMA acquired Highsmith Insurance Agency, a North Carolina-based independent insurance brokerage firm. • March – Marsh acquired Hoken Soken, Inc., a Japan-based insurance agency. • May – Marsh acquired Mountlodge Limited, a Scotland-based independent insurance broker and Lorant Martínez Salas y Compañía Agente de Seguros y de Fianzas, S.A. de C.V., a Mexico-based multi-line insurance broker. • June – MMA acquired Bleakley Insurance Services, a California-based provider of employee benefits solutions; Klein Agency, Inc., a Minnesota-based surety and property/casualty agency; and Insurance Associates, Inc., a Maryland-based independent insurance agency. • August – Marsh acquired John L. Wortham & Son, L.P., a Houston-based independent insurance broker. • October – MMA acquired Eustis Insurance, Inc., a Louisiana-based insurance agency. • November – MMA acquired James P. Murphy & Associates, Inc., a Connecticut-based insurance agency. • December – MMA acquired Otis-Magie Insurance Agency, Inc., a Minnesota-based insurance agency, and Marsh acquired Hector Insurance PCC Ltd, a U.K.-based captive management company. The Consulting segment completed eight acquisitions during 2018 . • January – Oliver Wyman acquired Draw Ltd., a U.K.-based digital transformation agency. • March – Oliver Wyman acquired 8Works Limited, a U.K.-based design thinking consultancy. • May – Mercer acquired EverBe SAS, a France-based Workday implementer and advisory firm; and Evolve Intelligence Pty Ltd., an Australia-based talent strategy firm. • June – Mercer acquired India Life Capital Private Ltd., an India-based investment advisor. • November – Mercer acquired Induslynk Training Services Private Ltd., an India-based talent assessment company, Pavilion Financial Corp., a Canada-based investment services firm and Summit Strategies Inc., a Missouri-based investment consulting firm. Total purchase consideration for acquisitions made during the first nine months of 2018 was $661 million , which consisted of cash paid of $553 million and deferred purchase consideration and estimated contingent consideration of $108 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 nine months of 2018, the Company also paid $59 million of deferred purchase consideration and $76 million of contingent consideration related to acquisitions made in prior years. Pro-Forma Information The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during 2019 and 2018. 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, 2018 and reflects acquisitions made in 2018 as if they occurred on January 1, 2017. 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 September 30, Nine Months Ended (In millions, except per share figures) 2019 2018 2019 2018 Revenue $ 3,967 $ 3,940 $ 12,830 $ 12,842 Net income attributable to the Company $ 306 $ 181 $ 1,445 $ 804 Basic net income per share attributable to the Company $ 0.61 $ 0.36 $ 2.85 $ 1.59 Diluted net income per share attributable to the Company $ 0.60 $ 0.36 $ 2.83 $ 1.57 The unaudited pro-forma information presented in the table above includes adjustments for acquisition related costs, the change in fair value of JLT acquisition related derivatives, bridge financing costs and the early extinguishment of debt: • A reduction of costs of $4 million for the three months ended September 30, 2019 . • An increase in costs of $662 million for the nine month period ended September 30, 2018 . Of this amount, $173 million represented a reduction of costs for the nine months ended September 30, 2019 , and the remainder was incurred in the third and fourth quarter of 2018. The consolidated statements of income include the results of operations of acquired companies since their respective acquisition dates. The consolidated statements of income for the three and nine month periods ended September 30, 2019 include approximately $352 million and $848 million of revenue, respectively, and operating losses of $69 million and $51 million , respectively, for acquisitions made in 2019. The consolidated statements of income for the three and nine month periods ended September 30, 2018 included $36 million and $ 50 million , respectively, of revenue and operating losses of $5 million and $7 million , respectively, related to acquisitions made in 2018. The Company incurred acquisition related costs, primarily related to legal, investment banking and U.K. stamp duty tax of $4 million and $99 million for the three and nine month periods ended September 30, 2019 , primarily related to the acquisition of JLT. These costs are included in other operating expenses in the Company's consolidated statement of income.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	9 Months Ended
	Sep. 30, 2019
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: September 30, (In millions) 2019 2018 Balance as of January 1, $ 9,599 $ 9,089 Goodwill acquired (a) 4,962 410 Other adjustments (b) (275 ) (64 ) Balance at September 30, $ 14,286 $ 9,435 (a) Primarily reflects $4.8 billion from the acquisition of JLT in 2019. (b) Primarily reflects the impact of foreign exchange. Of total goodwill acquired of $5.0 billion in 2019 , $201 million related to the Risk and Insurance Services segment is deductible for tax purposes. The goodwill arising from the acquisitions consist largely of the synergies and economies of scale expected from combining the operations of the Company and the acquired entities and the trained and assembled workforce acquired. The goodwill acquired was primarily assigned to the Risk and Insurance Services segment. Goodwill allocable to the Company’s reportable segments at September 30, 2019 is as follows: Risk and Insurance Services, $11.3 billion and Consulting, $3.0 billion . The gross cost and accumulated amortization of identified intangible assets at September 30, 2019 and December 31, 2018 are as follows: September 30, 2019 December 31, 2018 (In millions) Gross Cost Accumulated Amortization Net Carrying Amount Gross Cost Accumulated Amortization Net Carrying Amount Client Relationships $ 3,526 $ 824 $ 2,702 $ 1,970 $ 639 $ 1,331 Other (a) 364 197 167 259 153 106 Amortized intangibles $ 3,890 $ 1,021 $ 2,869 $ 2,229 $ 792 $ 1,437 (a) Primarily non-compete agreements, trade names and developed technology. Aggregate amortization expense for the nine months ended September 30, 2019 and 2018 was $235 million and $135 million , respectively. The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2019 (excludes amortization through September 30, 2019) $ 95 2020 354 2021 343 2022 327 2023 320 Subsequent years 1,430 $ 2,869

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2019
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"). 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 . Treasury Locks - Level 2 In connection with the JLT Transaction, to hedge the risk of increases in future interest rates prior to its issuance of fixed rate debt, in the fourth quarter of 2018 the Company entered into treasury locks related to $2 billion of expected issuances of senior notes in January 2019. The fair value at December 31, 2018 was based on the published treasury rate plus forward premium as of December 31, 2018, compared to the all in rate at the inception of the contract. These treasury locks were settled during the first quarter of 2019. Contingent Purchase Consideration Assets and Liability – Level 3 Purchase consideration for some acquisitions and dispositions made by the Company include contingent consideration arrangements. These arrangements typically provide for the payment of additional consideration if earnings or revenue targets are met over periods from 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 fair value at December 31, 2018 was determined using the probability distribution approach, comparing the all in forward rate to the foreign exchange rate for possible dates the JLT Transaction could close, discounted to the valuation date and adjusted for the fair value of the deal contingency feature. Determining the fair value of the FX Contract required significant management judgments or estimates about the potential closing dates of the transaction and remaining value of the deal contingency feature. 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 September 30, 2019 and December 31, 2018 . Identical Assets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Total (In millions) 09/30/19 12/31/18 09/30/19 12/31/18 09/30/19 12/31/18 09/30/19 12/31/18 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 5 $ 133 $ — $ — $ — $ — $ 5 $ 133 Mutual funds (a) 157 151 — — — — 157 151 Money market funds (b) 37 118 — — — — 37 118 Other equity investment (a) — — 8 8 — — 8 8 Contingent purchase consideration asset (a) — — — — 65 — 65 — Total assets measured at fair value $ 199 $ 402 $ 8 $ 8 $ 65 $ — $ 272 $ 410 Fiduciary Assets: U.S. Treasury Bills $ — $ 20 $ — $ — $ — $ — $ — $ 20 Money market funds 433 80 — — — — 433 80 Total fiduciary assets measured at fair value $ 433 $ 100 $ — $ — $ — $ — $ 433 $ 100 Liabilities: Contingent purchase consideration liability (c) $ — $ — $ — $ — $ 185 $ 183 $ 185 $ 183 Acquisition related derivative contracts — — — 116 — 325 — 441 Total liabilities measured at fair value $ — $ — $ — $ 116 $ 185 $ 508 $ 185 $ 624 (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 accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets. The contingent purchase consideration of $65 million related to the sale of JLT's global aerospace business is classified as a Level 3 asset. During the nine -month period ended September 30, 2019 , 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 nine month periods ended September 30, 2019 and 2018 : Three Months Ended Nine Months Ended (In millions) 2019 2018 2019 2018 Balance at beginning of period $ 196 $ 185 $ 508 $ 189 (Reductions) Additions (7 ) 8 33 34 Payments (13 ) (35 ) (58 ) (76 ) Revaluation Impact 6 8 26 19 Change in fair value of the FX contract — 100 (325 ) 100 Other (a) 3 2 1 2 Balance at September 30, $ 185 $ 268 $ 185 $ 268 (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 increase in the estimated fair value of such liabilities for prior-period acquisitions of $26 million in the nine -month period ended September 30, 2019 . A 5% increase in the projections used to estimate the contingent consideration would increase the liability by approximately $46 million . A 5% decrease would decrease the liability by approximately $39 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 $452 million and $287 million at September 30, 2019 and December 31, 2018 , respectively. Investments Accounted For Using the Equity Method of Accounting Investments in Public and Private Companies Alexander Forbes : The Company owns approximately 33% of the common stock of Alexander Forbes ("AF"), a South African company listed on the Johannesburg Stock Exchange, which it purchased in 2014 for 7.50 South African Rand ("Rand") per share. In the third quarter of 2018, the Company concluded the decline in value of the investment was other than temporary and recorded an impairment charge of $81 million reflecting the closing price of 4.95 Rand at September 30, 2018. As of September 30, 2019 , the carrying value of the Company's investment in AF was approximately $138 million . As of September 30, 2019 , the market value of the approximately 443 million shares of AF owned by the Company, based on the September 30, 2019 closing share price of 5.6 South African Rand per share, was $166 million . The Company has other investments in private insurance and consulting companies with a carrying value of $219 million and $61 million at September 30, 2019 and December 31, 2018, respectively. The Company’s investment in Alexander Forbes and its other 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 $95 million and $82 million at September 30, 2019 and December 31, 2018 , respectively. The carrying values of these private equity investments approximate fair value. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. The Company records in earnings its proportionate share of the change in fair value of the funds on the investment income line in the consolidated statements of income. These investments are included in other assets in the consolidated balance sheets. The Company recorded net investment income of $3 million and $10 million from these investments for the three and nine month periods ended September 30, 2019 , respectively, compared to net investment gains of $4 million and $14 million for the same periods in 2018. Other Investments At September 30, 2019 and December 31, 2018 , the Company held certain equity investments with readily determinable market values of $19 million and $146 million , respectively. The Company recorded investment gains on these investments of $4 million and $10 million in the three and nine month periods ended September 30, 2019 , respectively, and investment gains of $25 million and $43 million for the same periods in 2018. The Company also held investments without readily determinable market values of $47 million and $75 million at September 30, 2019 and December 31, 2018 , respectively. 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 as final settlement on the sale. During the second quarter of 2019, the Company disposed of its investment in Payscale and received proceeds of approximately $47 million

Derivatives

Derivatives	9 Months Ended
	Sep. 30, 2019
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. The Company recorded a gain of $31 million in the consolidated statement of income for the nine month period ended September 30, 2019, related to 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 fair value at December 31, 2018 was based on the published treasury rate plus forward premium as of December 31, 2018 compared to the all in rate at the inception of the contract. The contracts were not designated as an accounting hedge. The Company recorded an unrealized loss of $116 million related to the change in the fair value of this derivative in the consolidated statement of income for the full year ended December 31, 2018. 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 . An additional charge of $6 million was recorded in the consolidated statement of income for the nine month period ended September 30, 2019, related to the settlement of the Treasury lock contracts. 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 nine month period ended September 30, 2019, related to the 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 Transaction were denominated in U.S. dollars. In order to hedge its exposure against the risk of fluctuations between the GBP and the U.S. dollar, JLT entered into foreign exchange contracts and interest rate swaps, 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 nine month period ended September 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 for the nine month period ended September 30, 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 will be 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 September 30, 2019. During 2019, the U.S. dollar value of the euro notes decreased $39 million through September 30, 2019 due to the impact of foreign exchange rates, with a corresponding increase to foreign currency translation gains (losses).

Leases

Leases	9 Months Ended
	Sep. 30, 2019
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 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 was 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 98% of the Company’s lease obligations are for the use of office space. All of the Company’s material leases are operating leases. The Company assumed approximately $400 million , as of March 31, 2019, of ROU assets and lease liabilities from the JLT Transaction. As part of the Company's real estate rationalization plan related to the JLT Transaction, the Company has determined that approximately $7 million of its ROU assets have been impaired, and therefore, recorded a charge to the consolidated statement of income for the three and nine month periods ended September 30, 2019, with an offsetting reduction to ROU assets. The Company expects additional impairments as it continues to assess its future real estate requirements. The following chart provides additional information about the Company’s property leases: For the Three and Nine Months Ended September 30, 2019 (In millions) Three Months Ended September 30, Nine Months Ended September 30, Lease Cost: Operating lease cost $ 94 $ 276 Short-term lease cost 4 7 Variable lease cost 37 113 Sublease income (4 ) (12 ) Net lease cost $ 131 $ 384 Other information: Operating cash outflows from operating leases $ 288 Right of use assets obtained in exchange for new operating lease liabilities $ 112 Weighted-average remaining lease term – real estate 8.86 years Weighted-average discount rate – real estate leases 3.09 % Future minimum lease payments for the Company’s operating leases as of September 30, 2019 are as follows: Payment Dates (In millions) Real Estate Leases Remainder of 2019 $ 104 2020 406 2021 348 2022 324 2023 279 2024 233 Subsequent years 940 Total future lease payments 2,634 Less: Imputed interest (336 ) Total $ 2,298 Current lease liabilities $ 341 Long-term lease liabilities 1,957 Total lease liabilities $ 2,298 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 September 30, 2019 , the Company had additional operating real estate leases that had not yet commenced of $71 million . These operating leases will commence over the next 12 months. At December 31, 2018 , the aggregate future minimum rental commitments under all non-cancelable operating lease agreements are as follows: For the Year Ended December 31, Gross Rental Commitments Rentals from Subleases Net Rental Commitments (In millions of dollars) 2019 $ 361 $ 32 $ 329 2020 $ 340 $ 31 $ 309 2021 $ 277 $ 12 $ 265 2022 $ 252 $ 10 $ 242 2023 $ 214 $ 9 $ 205 Subsequent years $ 753 $ 32 $ 721

Retirement Benefits

Retirement Benefits	9 Months Ended
	Sep. 30, 2019
Defined Benefit Plan [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 September 30, 2019 the actual allocation for the Company's U.S. Plan was 62% equities and equity alternatives and 38% fixed income. The target allocation for the U.K. Plans at September 30, 2019 was 36% equities and equity alternatives and 64% fixed income. At September 30, 2019 , the actual allocation for the U.K. Plans was 33% equities and equity alternatives and 67% fixed income. The Company's U.K. Plans comprised approximately 81% of non-U.S. plan assets at December 31, 2018 . 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 Pension Plans As part of the JLT Transaction, the Company has assumed responsibility for a number of pension plans throughout the world, with $248 million of net pension liabilities as of March 31, 2019 (approximately $700 million of plan assets as of March 31, 2019), the most significant of which is the Jardine Lloyd Thompson U.K. Pension Scheme ("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 September 30, (In millions) 2019 2018 2019 2018 Service cost $ 10 $ 8 $ — $ 1 Interest cost 120 114 1 — Expected return on plan assets (214 ) (213 ) — — Amortization of prior service (credit) cost — — — (1 ) Recognized actuarial loss 25 36 (1 ) 1 Net periodic benefit (credit) cost $ (59 ) $ (55 ) $ — $ 1 Combined U.S. and significant non-U.S. Plans Pension Benefits Post-retirement Benefits For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Service cost $ 28 $ 25 $ — $ 1 Interest cost 360 349 2 2 Expected return on plan assets (644 ) (652 ) — — Amortization of prior service credit — (1 ) (1 ) (3 ) Recognized actuarial loss 77 110 (1 ) 1 Net periodic benefit (credit) cost $ (179 ) $ (169 ) $ — $ 1 Settlement loss 4 — — — Total (credit) cost $ (175 ) $ (169 ) $ — $ 1 Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Three Months Ended September 30, (In millions) 2019 2018 2019 2018 Compensation and benefits expense (Operating income) $ 10 $ 8 $ — $ 1 Other net benefit credits (69 ) (63 ) — — Total (credit) cost $ (59 ) $ (55 ) $ — $ 1 Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Compensation and benefits expense (Operating income) $ 28 $ 25 $ — $ 1 Other net benefit credits (203 ) (194 ) — — Total (credit) cost $ (175 ) $ (169 ) $ — $ 1 U.S. Plans only Pension Post-retirement For the Three Months Ended September 30, (In millions) 2019 2018 2019 2018 Interest cost $ 61 $ 58 $ 1 $ — Expected return on plan assets (86 ) (89 ) — — Recognized actuarial loss 11 14 (1 ) — Net periodic benefit credit $ (14 ) $ (17 ) $ — $ — U.S. Plans only Pension Post-retirement For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Interest cost $ 181 $ 176 $ 1 $ 1 Expected return on plan assets (257 ) (268 ) — — Amortization of prior service credit — — — (1 ) Recognized actuarial loss (credit) 33 41 (1 ) — Net periodic benefit credit $ (43 ) $ (51 ) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Three Months Ended September 30, (In millions) 2019 2018 2019 2018 Service cost $ 10 $ 8 $ — $ 1 Interest cost 59 56 — — Expected return on plan assets (128 ) (124 ) — — Amortization of prior service credit — — — (1 ) Recognized actuarial loss 14 22 — 1 Net periodic benefit (credit) cost $ (45 ) $ (38 ) $ — $ 1 Significant non-U.S. Plans only Pension Post-retirement For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Service cost $ 28 $ 25 $ — $ 1 Interest cost 179 173 1 1 Expected return on plan assets (387 ) (384 ) — — Amortization of prior service credit — (1 ) (1 ) (2 ) Recognized actuarial loss 44 69 — 1 Net periodic benefit (credit) cost $ (136 ) $ (118 ) $ — $ 1 Settlement loss 4 — — — Total (credit) cost $ (132 ) $ (118 ) $ — $ 1 The weighted average actuarial assumptions utilized to calculate the net periodic benefit costs for the U.S. and significant non-U.S. defined benefit plans are as follows: Combined U.S. and significant non-U.S. Plans Pension Post-retirement September 30, 2019 2018 2019 2018 Weighted average assumptions: Expected return on plan assets 5.74 % 5.83 % — — Discount Rate 3.48 % 3.07 % 3.65 % 3.21 % Rate of compensation increase 1.74 % 1.73 % — — The Company made approximately $85 million of contributions to its U.S. and non-U.S. defined benefit pension plans for the nine months ended September 30, 2019 . The Company expects to contribute approximately $32 million to its U.S. and non-U.S. defined benefit pension plans during the remainder of 2019 . 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 $106 million and $100 million for the nine months ended September 30, 2019 and 2018 , respectively. The cost of the U.K. DC Plans was $74 million and $61 million for the nine months ended September 30, 2019 and 2018 , respectively.

Debt

Debt	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Debt	Debt The Company’s outstanding debt is as follows: (In millions) September 30, December 31, Short-term: Commercial paper $ 325 $ — Term loan facility 300 — Current portion of long-term debt 514 314 1,139 314 Long-term: Senior notes – 2.35% due 2019 — 300 Senior notes – 2.35% due 2020 500 499 Senior notes – 3.50% due 2020 698 — Senior notes – 4.80% due 2021 499 499 Senior notes - Floating rate due 2021 298 — Senior notes – 2.75% due 2022 498 497 Senior notes – 3.30% due 2023 348 348 Senior notes – 4.05% due 2023 249 249 Senior notes – 3.50% due 2024 597 597 Senior notes – 3.875% due 2024 993 — Senior notes – 3.50% due 2025 497 496 Senior notes – 1.349% due 2026 603 — Senior notes – 3.75% due 2026 597 596 Senior notes – 4.375% due 2029 1,499 — Senior notes – 1.979% due 2030 602 — Senior notes – 5.875% due 2033 298 297 Senior notes – 4.75% due 2039 494 — Senior notes – 4.35% due 2047 492 492 Senior notes – 4.20% due 2048 592 592 Senior notes – 4.90% due 2049 1,237 — Mortgage – 5.70% due 2035 347 358 Other 5 4 11,943 5,824 Less current portion 514 314 $ 11,429 $ 5,510 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 $325 million of commercial paper outstanding at September 30, 2019 at an effective interest rate of 2.29% . On September 18, 2018, the Company entered into a bridge loan agreement to finance the JLT Transaction. The bridge loan agreement provided for commitments in the aggregate principal amount of £5.2 billion . In 2018, the Company paid approximately $35 million of customary upfront fees related to the bridge loan at the inception of the loan commitment, of which $30 million was amortized in 2018 and $5 million in the first quarter of 2019 as interest expense based on the period of time the facility was expected to be in effect (including any loans outstanding). The Company terminated its bridge loan agreement on April 1, 2019. 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. 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 above). 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 March 2019, the Company closed on $300 million one -year and $300 million three -year term loan facilities. 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 below. The Company had $300 million of borrowings outstanding under the one -year term facility at September 30, 2019 at an average borrowing rate of 3.05% . In August 2019, the Company terminated the $300 million three-year term facility. The outstanding term loan expires on March 2020 and will not be impacted by the replacement of LIBOR. 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. In September 2019, the Company repaid $300 million of maturing senior notes. In March 2018, the Company issued $600 million of 4.20% senior notes due 2048. The Company used the net proceeds for general corporate purposes. In October 2018, the Company and certain of its foreign subsidiaries increased its multi-currency five -year unsecured revolving credit facility from $1.5 billion to $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. There were no borrowings outstanding under this facility at September 30, 2019 . 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. 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. September 30, 2019 December 31, 2018 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Short-term debt $ 1,139 $ 1,140 $ 314 $ 313 Long-term debt $ 11,429 $ 12,666 $ 5,510 $ 5,437 The fair value of the Company’s short-term debt consists primarily of commercial paper, borrowings from the term loan facility 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- and long-term debt would be classified as Level 2 in the fair value hierarchy.

Restructuring Costs

Restructuring Costs	9 Months Ended
	Sep. 30, 2019
Restructuring and Related Activities [Abstract]
Restructuring Costs	Restructuring Costs JLT Related Integration and Restructuring The Company has begun its integration and restructuring activities related to JLT. The process will involve combining the business practices and co-locating colleagues in most geographies, rationalization of real estate leases around the world, realization of synergies and migration of legacy JLT systems onto MMC’s information technology environment and security protocols, consulting fees related to integration management processes and legal fees related to the rationalization of legal entity structures that will 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 at least $375 million in connection with the integration and restructuring of the combined businesses, primarily related to severance, real estate rationalization, technology, consulting fees related to the management of the integration processes and legal fees related to the rationalization of legal entity structures. The Company expects to incur these costs over a three- year period, and has incurred $192 million to date. These integration and restructuring plans are still developing, and these estimates may change as the Company completes its detailed plans for each business and location. In connection with the JLT integration and restructuring, in the third quarter of 2019, the Company incurred costs of $77 million : $58 million in RIS, $5 million in Consulting, and $14 million in Corporate. For the nine month period ended September 30, 2019, costs incurred were $134 million in RIS, $10 million in Consulting, and $48 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 September 30, 2019 , 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 92 21 9 70 192 Cash payments (59 ) (5 ) (9 ) (70 ) (143 ) Non-cash charges — (7 ) — — (7 ) Liability at 9/30/19 $ 33 $ 9 $ — $ — $ 42 (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 the second quarter of 2018, Marsh initiated a program to simplify the organization through reduced management layers and more common structures across regions and businesses to more closely align with its more formalized segmentation strategy across large risk management, middle market corporate, and small commercial & personal segments. These efforts are expected to create increased efficiencies and additional capacity for reinvestment in people and technology. The Company incurred severance and consulting costs of $6 million for the nine month period ended September 30, 2019 , related to this initiative. 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 $10 million and $43 million for the three and nine month periods, ended September 30, 2019 , respectively, related to this initiative. In addition to the changes discussed above, the Company incurred $7 million of restructuring costs related to severance and future rent under non-cancelable leases, primarily in Corporate. Details of the other restructuring activity from January 1, 2018 through September 30, 2019 , which includes liabilities from actions prior to 2019 , are as follows: (In millions) Liability at 1/1/18 Amounts Accrued Cash Paid Other Liability at 12/31/18 Amounts Accrued Cash Paid Other Liability at 9/30/19 Severance $ 15 $ 137 $ (77 ) $ (2 ) $ 73 $ 44 $ (95 ) $ (4 ) $ 18 Future rent under non-cancelable leases and other costs 50 24 (37 ) 2 39 12 (13 ) (6 ) $ 32 Total $ 65 $ 161 $ (114 ) $ — $ 112 $ 56 $ (108 ) $ (10 ) $ 50 The expenses associated with the above initiatives are included in compensation and benefits and other operating expenses in the consolidated statements of income. The liabilities associated with these initiatives are classified on the consolidated balance sheets as accounts payable and accrued liabilities, other liabilities or accrued compensation and employee benefits, depending on the nature of the items. These programs are substantially completed as of September 30, 2019.

Common Stock

Common Stock	9 Months Ended
	Sep. 30, 2019
Equity [Abstract]
Common Stock	Common Stock During the first nine months of 2019 , the Company repurchased approximately 3.1 million shares of its common stock for consideration of $300 million . In November 2016, 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 September 30, 2019 , the Company remained authorized to repurchase up to approximately $566 million in shares of its common stock. There is no time limit on the authorization. During the first nine months of 2018 , the Company repurchased approximately 8.2 million shares of its common stock for consideration of $675 million . The Company issued approximately 4.2 million and 3.0 million shares related to stock compensation and employee stock purchase plans during the first nine months of 2019 and 2018 , respectively.

Claims, Lawsuits And Other Cont

Claims, Lawsuits And Other Contingencies	9 Months Ended
	Sep. 30, 2019
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. By virtue 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 services for corporate and public sector clients, the provision of investment advice and investment management services to pension plans, the provision of advice relating to pension buy-out transactions and the provision of consulting services relating to the drafting and interpretation of trust deeds and other documentation governing pension plans. These claims 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 have 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. We are cooperating with these investigations and are conducting our own reviews. At this time, we are unable to predict their likely timing, outcome or ultimate impact. There can be no assurance that the ultimate resolution of these or any related matters will not have a material adverse effect on our consolidated results of operations, financial condition or cash flows. 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 it was commissioning a Skilled Person review of JLT’s ETV advice. In February 2019, prior to the completion of the acquisition, JLT disclosed that it had recorded a net charge of £38.4 million (or approximately $49.2 million ) arising from the Skilled Person report and ETV review, reflecting estimated net costs offset by potential insurance and indemnification recoveries. Pending the outcome of the FCA’s review, and based on our review as of September 30, 2019, the Company has a gross liability of 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 September 30, 2019 , 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	9 Months Ended
	Sep. 30, 2019
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 2018 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 nine -month periods ended September 30, 2019 and 2018 are as follows: Three Months Ended September 30, Nine Months Ended (In millions) Revenue Operating Income (Loss) Revenue Operating Income (Loss) 2019– Risk and Insurance Services $ 2,206 (a) $ 218 $ 7,203 (c) $ 1,468 Consulting 1,785 (b) 317 5,258 (d) 874 Total Operating Segments 3,991 535 12,461 2,342 Corporate/Eliminations (23 ) (68 ) (73 ) (257 ) Total Consolidated $ 3,968 $ 467 $ 12,388 $ 2,085 2018– Risk and Insurance Services $ 1,863 (a) $ 293 $ 6,303 (c) $ 1,481 Consulting 1,656 (b) 291 4,974 (d) 805 Total Operating Segments 3,519 584 11,277 2,286 Corporate/Eliminations (15 ) (43 ) (39 ) (146 ) Total Consolidated $ 3,504 $ 541 $ 11,238 $ 2,140 (a) Includes inter-segment revenue of $3 million and $4 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $31 million and $18 million in 2019 and 2018 , respectively, and equity method income of $10 million and $4 million in 2019 and 2018 , respectively and $51 million related to the sale of business in 2018 . (b) Includes inter-segment revenue of $20 million and $11 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $1 million in 2018 , and equity method income of $4 million in 2018 . (c) Includes inter-segment revenue of $7 million and $5 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $80 million and $46 million in 2019 and 2018 , respectively, and equity method income of $16 million and $10 million in 2019 and 2018 , respectively and $51 million related to the sale of business in 2018 . (d) Includes inter-segment revenue of $66 million and $34 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $2 million and $3 million in 2019 and 2018 , respectively and equity method income of $10 million and $12 million in 2019 and in 2018 , respectively. Details of operating segment revenue for the three and nine -month periods ended September 30, 2019 and 2018 are as follows: Three Months Ended September 30, Nine Months Ended (In millions) 2019 2018 2019 2018 Risk and Insurance Services Marsh $ 1,923 $ 1,643 $ 5,850 $ 5,106 Guy Carpenter 283 220 1,353 1,197 Total Risk and Insurance Services 2,206 1,863 7,203 6,303 Consulting Mercer 1,280 1,175 3,695 3,504 Oliver Wyman Group 505 481 1,563 1,470 Total Consulting 1,785 1,656 5,258 4,974 Total Operating Segments 3,991 3,519 12,461 11,277 Corporate / Eliminations (23 ) (15 ) (73 ) (39 ) Total $ 3,968 $ 3,504 $ 12,388 $ 11,238

New Accounting Guidance

New Accounting Guidance	9 Months Ended
	Sep. 30, 2019
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Guidance	New Accounting Guidance 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 Effective January 1, 2018: The following new accounting standards were adopted using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of January 1, 2018: Revenue Recognition In May 2014, the FASB issued new accounting guidance related to revenue from contracts with customers. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Company adopted the new guidance effective January 1, 2018, using the modified retrospective method, which applies the new guidance beginning with the year of adoption, with the cumulative effect of initially applying the guidance recognized as an adjustment to retained earnings at January 1, 2018. The cumulative effect of adopting the standard, net of tax, on January 1, 2018 resulted in an increase to the opening balance of retained earnings of $364 million , with offsetting increases/decreases to other balance sheet accounts, e.g. accounts receivable, other assets and deferred income taxes. Recognition and Measurement of Financial Instruments In January 2016, the FASB issued new guidance intended to improve the recognition and measurement of financial instruments. The new guidance requires investments in equity securities (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income; requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (i.e., securities or loans and receivables) on the balance sheet or the accompanying notes to the financial statements; eliminates the requirement for public business entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet; and requires a reporting organization to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk (also referred to as "own credit") when the organization has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. The Company adopted the new accounting guidance effective January 1, 2018, recording a cumulative-effect adjustment increase to retained earnings as of the beginning of the period of adoption of $14 million , reflecting the reclassification of cumulative unrealized gains, net of tax as of December 31, 2017 from accumulated other comprehensive income to retained earnings. Income Tax Consequences of Intra-Entity Transfers In October 2016, the FASB also issued new guidance which requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The new guidance eliminates the exception for an intra-entity transfer of an asset other than inventory. The new guidance is effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The new guidance must be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company adopted the new guidance effective January 1, 2018, recording a cumulative-effect adjustment decrease to retained earnings of approximately $14 million as of the beginning of the period of adoption. New Accounting Pronouncements Not Yet Adopted 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 guidance is effective for fiscal years beginning after December 15, 2019, including interim periods therein. 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. 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. 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 guidance is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company does not expect the adoption of this standard to have a material impact on its financial position or results of operations. In June 2016, the FASB issued new guidance on the impairment of financial instruments. The new guidance adds an impairment model (known as the current expected credit loss (CECL) 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 new standard is effective for public companies for annual reporting periods beginning after December 15, 2019, and interim periods therein. The Company is currently evaluating the impact of this standard, but does not expect the adoption of this standard will have a material impact on its financial position or results of operations.

Principles of Consolidation a_2

Principles of Consolidation and Other Matters (Policies)	9 Months Ended
	Sep. 30, 2019
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.
Investments	The caption "Investment income" in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in earnings. It includes, when applicable, other than temporary declines in the value of securities, mark-to-market increases or decreases in equity investments with readily determinable fair values and equity method gains or losses on the Company's investments in private equity funds. The Company holds investments in certain private equity funds 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.
Leases	Effective January 1, 2019, the Company adopted the new accounting standard related to leases. Under the new standard, a lessee is required to recognize assets and liabilities for its leases with lease terms of more than 12 months. The Company adopted this new standard using the modified retrospective method, which applies the new guidance beginning with the year of adoption, with the cumulative effect of initially applying the standard recognized as an adjustment to retained earnings at January 1, 2019. There was no cumulative-effect adjustment required to be recorded to retained earnings upon transition. Prior period results have not been restated to reflect the adoption of this new standard.
Income Taxes	The Company's effective tax rate in the third quarter of 2019 was 26.0% compared with 27.5% in the third quarter of 2018 . The effective tax rates for the first nine months of 2019 and 2018 were 27.8% and 25.2% , respectively. The rate in the first nine 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 Transaction. The rate in the third quarter of 2018 as well as the first nine months of 2018 reflect the impact of a charge related to the Company’s investment in Alexander Forbes as discussed in Note 10, largely offset by favorable adjustments to the estimated impact of tax reform. Both periods reflect the effect of other 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 is routinely examined by tax authorities in the jurisdictions in which it has significant operations. The Company regularly considers the likelihood of assessments in each of the taxing jurisdictions resulting from examinations. When evaluating the potential imposition of penalties, the Company considers a number of relevant factors under penalty statutes, including appropriate disclosure of the tax return position, the existence of legal authority supporting the Company's position, and reliance on the opinion of professional tax advisors.
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"). 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 . Treasury Locks - Level 2 In connection with the JLT Transaction, to hedge the risk of increases in future interest rates prior to its issuance of fixed rate debt, in the fourth quarter of 2018 the Company entered into treasury locks related to $2 billion of expected issuances of senior notes in January 2019. The fair value at December 31, 2018 was based on the published treasury rate plus forward premium as of December 31, 2018, compared to the all in rate at the inception of the contract. These treasury locks were settled during the first quarter of 2019. Contingent Purchase Consideration Assets and Liability – Level 3 Purchase consideration for some acquisitions and dispositions made by the Company include contingent consideration arrangements. These arrangements typically provide for the payment of additional consideration if earnings or revenue targets are met over periods from 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 fair value at December 31, 2018 was determined using the probability distribution approach, comparing the all in forward rate to the foreign exchange rate for possible dates the JLT Transaction could close, discounted to the valuation date and adjusted for the fair value of the deal contingency feature. Determining the fair value of the FX Contract required significant management judgments or estimates about the potential closing dates of the transaction and remaining value of the deal contingency feature.
New Accounting Pronouncements	New Accounting Guidance 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 Effective January 1, 2018: The following new accounting standards were adopted using a modified retrospective approach through a cumulative-effect adjustment to retained earnings as of January 1, 2018: Revenue Recognition In May 2014, the FASB issued new accounting guidance related to revenue from contracts with customers. The core principle of the guidance is that an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The Company adopted the new guidance effective January 1, 2018, using the modified retrospective method, which applies the new guidance beginning with the year of adoption, with the cumulative effect of initially applying the guidance recognized as an adjustment to retained earnings at January 1, 2018. The cumulative effect of adopting the standard, net of tax, on January 1, 2018 resulted in an increase to the opening balance of retained earnings of $364 million , with offsetting increases/decreases to other balance sheet accounts, e.g. accounts receivable, other assets and deferred income taxes. Recognition and Measurement of Financial Instruments In January 2016, the FASB issued new guidance intended to improve the recognition and measurement of financial instruments. The new guidance requires investments in equity securities (except those accounted for under the equity method of accounting, or those that result in consolidation of the investee) to be measured at fair value with changes in fair value recognized in net income; requires public business entities to use the exit price notion when measuring the fair value of financial instruments for disclosure purposes; requires separate presentation of financial assets and financial liabilities by measurement category and form of financial asset (i.e., securities or loans and receivables) on the balance sheet or the accompanying notes to the financial statements; eliminates the requirement for public business entities to disclose the method(s) and significant assumptions used to estimate the fair value that is required to be disclosed for financial instruments measured at amortized cost on the balance sheet; and requires a reporting organization to present separately in other comprehensive income the portion of the total change in the fair value of a liability resulting from a change in the instrument-specific credit risk (also referred to as "own credit") when the organization has elected to measure the liability at fair value in accordance with the fair value option for financial instruments. The Company adopted the new accounting guidance effective January 1, 2018, recording a cumulative-effect adjustment increase to retained earnings as of the beginning of the period of adoption of $14 million , reflecting the reclassification of cumulative unrealized gains, net of tax as of December 31, 2017 from accumulated other comprehensive income to retained earnings. Income Tax Consequences of Intra-Entity Transfers In October 2016, the FASB also issued new guidance which requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The new guidance eliminates the exception for an intra-entity transfer of an asset other than inventory. The new guidance is effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The new guidance must be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company adopted the new guidance effective January 1, 2018, recording a cumulative-effect adjustment decrease to retained earnings of approximately $14 million as of the beginning of the period of adoption. New Accounting Pronouncements Not Yet Adopted 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 guidance is effective for fiscal years beginning after December 15, 2019, including interim periods therein. 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. 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. 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 guidance is effective for annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted. The Company does not expect the adoption of this standard to have a material impact on its financial position or results of operations. In June 2016, the FASB issued new guidance on the impairment of financial instruments. The new guidance adds an impairment model (known as the current expected credit loss (CECL) 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 new standard is effective for public companies for annual reporting periods beginning after December 15, 2019, and interim periods therein. The Company is currently evaluating the impact of this standard, but does not expect the adoption of this standard will have a material impact on its financial position or results of operations.

Revenue (Tables)

Revenue (Tables)	9 Months Ended
	Sep. 30, 2019
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following schedule disaggregates components of the Company's revenue: Three Months Ended September 30, Nine Months Ended (In millions) 2019 2019 Marsh: EMEA $ 536 $ 1,821 Asia Pacific 242 698 Latin America 110 304 Total International 888 2,823 U.S./Canada 1,014 2,972 Total Marsh 1,902 5,795 Guy Carpenter 273 1,328 Subtotal 2,175 7,123 Fiduciary interest income 31 80 Total Risk and Insurance Services $ 2,206 $ 7,203 Mercer: Wealth $ 592 $ 1,748 Health 441 1,341 Career 247 606 Total Mercer 1,280 3,695 Oliver Wyman 505 1,563 Total Consulting $ 1,785 $ 5,258
Contract with Customer, Asset and Liability	The following schedule provides contract assets and contract liabilities information from contracts with customers. (In millions) September 30, 2019 January 1, 2019 Contract Assets $ 240 $ 112 Contract Liabilities $ 611 $ 545

Per Share Data (Tables)

Per Share Data (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Basic and Diluted EPS Calculation	Basic and Diluted EPS Calculation Three Months Ended September 30, Nine Months Ended (In millions, except per share amounts) 2019 2018 2019 2018 Net income before non-controlling interests $ 306 $ 279 $ 1,377 $ 1,511 Less: Net income attributable to non-controlling interests 3 3 26 14 Net income attributable to the Company $ 303 $ 276 $ 1,351 $ 1,497 Basic weighted average common shares outstanding 506 504 506 506 Dilutive effect of potentially issuable common shares 5 6 5 6 Diluted weighted average common shares outstanding 511 510 511 512 Average stock price used to calculate common stock equivalents $ 99.97 $ 84.68 $ 94.75 $ 83.05

Supplemental Disclosures to t_2

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Tables)	9 Months Ended
	Sep. 30, 2019
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 nine -month periods ended September 30, 2019 and 2018 . (In millions) 2019 2018 Assets acquired, excluding cash $ 8,619 $ 679 Liabilities assumed (2,758 ) (35 ) Non-controlling interests assumed (295 ) — Contingent/deferred purchase consideration (66 ) (108 ) Net cash outflow for current year acquisitions $ 5,500 $ 536 (In millions) 2019 2018 Interest paid $ 387 $ 225 Income taxes paid, net of refunds $ 442 $ 455

Other Comprehensive Income (L_2

Other Comprehensive Income (Loss) (Tables)	9 Months Ended
	Sep. 30, 2019
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 nine -month periods ended September 30, 2019 and 2018 , including amounts reclassified out of AOCI, are as follows: (In millions) Unrealized Investment Gains (Losses) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of July 1, 2019 $ — $ (2,942 ) $ (1,585 ) $ (4,527 ) Other comprehensive income before reclassifications — 56 (475 ) (419 ) Amounts reclassified from accumulated other comprehensive income — 15 — 15 Net current period other comprehensive income (loss) — 71 (475 ) (404 ) Balance as of September 30, 2019 $ — $ (2,871 ) $ (2,060 ) $ (4,931 ) (In millions) Unrealized Investment Gains (Losses) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of July 1, 2018 $ — $ (2,807 ) $ (1,458 ) $ (4,265 ) Other comprehensive income (loss) before reclassifications — (13 ) (242 ) (255 ) Amounts reclassified from accumulated other comprehensive income — 32 — 32 Net current period other comprehensive income (loss) — 19 (242 ) (223 ) Balance as of September 30, 2018 $ — $ (2,788 ) $ (1,700 ) $ (4,488 ) (In millions) Unrealized Investment Gains (Losses) 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 (loss) income before reclassifications — 26 (366 ) (340 ) Amounts reclassified from accumulated other comprehensive income — 56 — 56 Net current period other comprehensive income (loss) — 82 (366 ) (284 ) Balance as of September 30, 2019 $ — $ (2,871 ) $ (2,060 ) $ (4,931 ) (In millions) Unrealized Investment Gains (Losses) Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2017 $ 14 $ (2,892 ) $ (1,165 ) $ (4,043 ) Cumulative effect of amended accounting standard (14 ) — — (14 ) Other comprehensive income (loss) before reclassifications — 16 (535 ) (519 ) Amounts reclassified from accumulated other comprehensive income — 88 — 88 Net current period other comprehensive income (loss) — 104 (535 ) (431 ) Balance as of September 30, 2018 $ — $ (2,788 ) $ (1,700 ) $ (4,488 )
Schedule of Components of Comprehensive Income (Loss)	The components of other comprehensive income (loss) for the three and nine -month periods ended September 30, 2019 and 2018 are as follows: Three Months Ended September 30, 2019 2018 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (475 ) $ — $ (475 ) $ (237 ) $ 5 $ (242 ) 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) 25 6 19 36 7 29 Effect of remeasurement (a) (8 ) (2 ) (6 ) 3 — 3 Effect of settlement (a) 2 — 2 — — — Subtotal 18 3 15 38 6 32 Foreign currency translation adjustments 64 8 56 (15 ) (2 ) (13 ) Pension/post-retirement plans gains 82 11 71 23 4 19 Other comprehensive (loss) income $ (393 ) $ 11 $ (404 ) $ (214 ) $ 9 $ (223 ) (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. Nine Months Ended September 30, 2019 2018 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (366 ) $ — $ (366 ) $ (538 ) $ (3 ) $ (535 ) Pension/post-retirement plans: Amortization of (gains) losses included in net periodic pension cost: Prior service credits (a) (2 ) (1 ) (1 ) (3 ) (1 ) (2 ) Net actuarial losses (a) 77 18 59 110 23 87 Effect of remeasurement (a) (9 ) (2 ) (7 ) 3 — 3 Effect of settlement (a) 6 1 5 — — — Subtotal 72 16 56 110 22 88 Foreign currency translation adjustments 30 4 26 21 5 16 Pension/post-retirement plans gains 102 20 82 131 27 104 Other comprehensive (loss) income $ (264 ) $ 20 $ (284 ) $ (407 ) $ 24 $ (431 ) (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)	9 Months Ended
	Sep. 30, 2019
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 2019 based on the estimated fair values for JLT and other acquisitions as of their respective acquisition dates: Acquisitions through September 30, 2019 (In millions) JLT Other Total Acquisitions Cash $ 5,568 $ 291 $ 5,859 Estimated fair value of deferred/contingent consideration — 66 66 Total consideration $ 5,568 $ 357 $ 5,925 Allocation of purchase price: Cash and cash equivalents $ 353 $ 6 $ 359 Accounts receivable, net 714 5 719 Other current assets 143 — 143 Fixed assets, net 89 2 91 Other intangible assets 1,613 143 1,756 Goodwill 4,761 201 4,962 Right of use assets 382 — 382 Deferred tax assets 65 — 65 Other assets 493 8 501 Total assets acquired 8,613 365 8,978 Current liabilities 689 5 694 Fiduciary liabilities 1,275 — 1,275 Less - fiduciary assets (1,275 ) — (1,275 ) Long-term debt 1,044 — 1,044 Long-term lease liability 389 — 389 Pension, post-retirement and post-employment liabilities 248 — 248 Liabilities for errors and omissions 31 — 31 Other liabilities 349 3 352 Total liabilities assumed 2,750 8 2,758 Non controlling interests 295 — 295 Net assets acquired $ 5,568 $ 357 $ 5,925
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	The following chart provides information about intangible assets acquired during 2019 : Intangible assets through September 30, 2019 (In millions) JLT Other Total JLT Weighted Average Amortization Period Other Weighted Average Amortization Period Client relationships $ 1,511 $ 136 $ 1,647 13 years 12 years Other 102 7 109 4 years 3 years $ 1,613 $ 143 $ 1,756
Pro-Forma Information	The following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during 2019 and 2018. 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, 2018 and reflects acquisitions made in 2018 as if they occurred on January 1, 2017. 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 September 30, Nine Months Ended (In millions, except per share figures) 2019 2018 2019 2018 Revenue $ 3,967 $ 3,940 $ 12,830 $ 12,842 Net income attributable to the Company $ 306 $ 181 $ 1,445 $ 804 Basic net income per share attributable to the Company $ 0.61 $ 0.36 $ 2.85 $ 1.59 Diluted net income per share attributable to the Company $ 0.60 $ 0.36 $ 2.83 $ 1.57

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	9 Months Ended
	Sep. 30, 2019
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the Carrying Amount of Goodwill	Changes in the carrying amount of goodwill are as follows: September 30, (In millions) 2019 2018 Balance as of January 1, $ 9,599 $ 9,089 Goodwill acquired (a) 4,962 410 Other adjustments (b) (275 ) (64 ) Balance at September 30, $ 14,286 $ 9,435 (a) Primarily reflects $4.8 billion from the acquisition of JLT in 2019. (b) Primarily reflects the impact of foreign exchange.
Amortized Intangible Assets	The gross cost and accumulated amortization of identified intangible assets at September 30, 2019 and December 31, 2018 are as follows: September 30, 2019 December 31, 2018 (In millions) Gross Cost Accumulated Amortization Net Carrying Amount Gross Cost Accumulated Amortization Net Carrying Amount Client Relationships $ 3,526 $ 824 $ 2,702 $ 1,970 $ 639 $ 1,331 Other (a) 364 197 167 259 153 106 Amortized intangibles $ 3,890 $ 1,021 $ 2,869 $ 2,229 $ 792 $ 1,437 (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 2019 (excludes amortization through September 30, 2019) $ 95 2020 354 2021 343 2022 327 2023 320 Subsequent years 1,430 $ 2,869

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 and December 31, 2018 . Identical Assets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Total (In millions) 09/30/19 12/31/18 09/30/19 12/31/18 09/30/19 12/31/18 09/30/19 12/31/18 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 5 $ 133 $ — $ — $ — $ — $ 5 $ 133 Mutual funds (a) 157 151 — — — — 157 151 Money market funds (b) 37 118 — — — — 37 118 Other equity investment (a) — — 8 8 — — 8 8 Contingent purchase consideration asset (a) — — — — 65 — 65 — Total assets measured at fair value $ 199 $ 402 $ 8 $ 8 $ 65 $ — $ 272 $ 410 Fiduciary Assets: U.S. Treasury Bills $ — $ 20 $ — $ — $ — $ — $ — $ 20 Money market funds 433 80 — — — — 433 80 Total fiduciary assets measured at fair value $ 433 $ 100 $ — $ — $ — $ — $ 433 $ 100 Liabilities: Contingent purchase consideration liability (c) $ — $ — $ — $ — $ 185 $ 183 $ 185 $ 183 Acquisition related derivative contracts — — — 116 — 325 — 441 Total liabilities measured at fair value $ — $ — $ — $ 116 $ 185 $ 508 $ 185 $ 624 (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 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 nine month periods ended September 30, 2019 and 2018 : Three Months Ended Nine Months Ended (In millions) 2019 2018 2019 2018 Balance at beginning of period $ 196 $ 185 $ 508 $ 189 (Reductions) Additions (7 ) 8 33 34 Payments (13 ) (35 ) (58 ) (76 ) Revaluation Impact 6 8 26 19 Change in fair value of the FX contract — 100 (325 ) 100 Other (a) 3 2 1 2 Balance at September 30, $ 185 $ 268 $ 185 $ 268 (a) Primarily reflects the impact of foreign exchange.

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Lease Cost and Additional Information	The following chart provides additional information about the Company’s property leases: For the Three and Nine Months Ended September 30, 2019 (In millions) Three Months Ended September 30, Nine Months Ended September 30, Lease Cost: Operating lease cost $ 94 $ 276 Short-term lease cost 4 7 Variable lease cost 37 113 Sublease income (4 ) (12 ) Net lease cost $ 131 $ 384 Other information: Operating cash outflows from operating leases $ 288 Right of use assets obtained in exchange for new operating lease liabilities $ 112 Weighted-average remaining lease term – real estate 8.86 years Weighted-average discount rate – real estate leases 3.09 %
Future Minimum Lease Payments for Operating Leases	Future minimum lease payments for the Company’s operating leases as of September 30, 2019 are as follows: Payment Dates (In millions) Real Estate Leases Remainder of 2019 $ 104 2020 406 2021 348 2022 324 2023 279 2024 233 Subsequent years 940 Total future lease payments 2,634 Less: Imputed interest (336 ) Total $ 2,298 Current lease liabilities $ 341 Long-term lease liabilities 1,957 Total lease liabilities $ 2,298 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.
Aggregate Fixed Future Minimum Commitments	At December 31, 2018 , the aggregate future minimum rental commitments under all non-cancelable operating lease agreements are as follows: For the Year Ended December 31, Gross Rental Commitments Rentals from Subleases Net Rental Commitments (In millions of dollars) 2019 $ 361 $ 32 $ 329 2020 $ 340 $ 31 $ 309 2021 $ 277 $ 12 $ 265 2022 $ 252 $ 10 $ 242 2023 $ 214 $ 9 $ 205 Subsequent years $ 753 $ 32 $ 721

Retirement Benefits (Tables)

Retirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2019
Defined Benefit Plan [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 September 30, (In millions) 2019 2018 2019 2018 Service cost $ 10 $ 8 $ — $ 1 Interest cost 120 114 1 — Expected return on plan assets (214 ) (213 ) — — Amortization of prior service (credit) cost — — — (1 ) Recognized actuarial loss 25 36 (1 ) 1 Net periodic benefit (credit) cost $ (59 ) $ (55 ) $ — $ 1 Combined U.S. and significant non-U.S. Plans Pension Benefits Post-retirement Benefits For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Service cost $ 28 $ 25 $ — $ 1 Interest cost 360 349 2 2 Expected return on plan assets (644 ) (652 ) — — Amortization of prior service credit — (1 ) (1 ) (3 ) Recognized actuarial loss 77 110 (1 ) 1 Net periodic benefit (credit) cost $ (179 ) $ (169 ) $ — $ 1 Settlement loss 4 — — — Total (credit) cost $ (175 ) $ (169 ) $ — $ 1 Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Three Months Ended September 30, (In millions) 2019 2018 2019 2018 Compensation and benefits expense (Operating income) $ 10 $ 8 $ — $ 1 Other net benefit credits (69 ) (63 ) — — Total (credit) cost $ (59 ) $ (55 ) $ — $ 1 Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. Plans Pension Post-retirement For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Compensation and benefits expense (Operating income) $ 28 $ 25 $ — $ 1 Other net benefit credits (203 ) (194 ) — — Total (credit) cost $ (175 ) $ (169 ) $ — $ 1 U.S. Plans only Pension Post-retirement For the Three Months Ended September 30, (In millions) 2019 2018 2019 2018 Interest cost $ 61 $ 58 $ 1 $ — Expected return on plan assets (86 ) (89 ) — — Recognized actuarial loss 11 14 (1 ) — Net periodic benefit credit $ (14 ) $ (17 ) $ — $ — U.S. Plans only Pension Post-retirement For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Interest cost $ 181 $ 176 $ 1 $ 1 Expected return on plan assets (257 ) (268 ) — — Amortization of prior service credit — — — (1 ) Recognized actuarial loss (credit) 33 41 (1 ) — Net periodic benefit credit $ (43 ) $ (51 ) $ — $ — Significant non-U.S. Plans only Pension Post-retirement For the Three Months Ended September 30, (In millions) 2019 2018 2019 2018 Service cost $ 10 $ 8 $ — $ 1 Interest cost 59 56 — — Expected return on plan assets (128 ) (124 ) — — Amortization of prior service credit — — — (1 ) Recognized actuarial loss 14 22 — 1 Net periodic benefit (credit) cost $ (45 ) $ (38 ) $ — $ 1 Significant non-U.S. Plans only Pension Post-retirement For the Nine Months Ended September 30, (In millions) 2019 2018 2019 2018 Service cost $ 28 $ 25 $ — $ 1 Interest cost 179 173 1 1 Expected return on plan assets (387 ) (384 ) — — Amortization of prior service credit — (1 ) (1 ) (2 ) Recognized actuarial loss 44 69 — 1 Net periodic benefit (credit) cost $ (136 ) $ (118 ) $ — $ 1 Settlement loss 4 — — — Total (credit) cost $ (132 ) $ (118 ) $ — $ 1
Schedule of Assumptions Used	The weighted average actuarial assumptions utilized to calculate the net periodic benefit costs for the U.S. and significant non-U.S. defined benefit plans are as follows: Combined U.S. and significant non-U.S. Plans Pension Post-retirement September 30, 2019 2018 2019 2018 Weighted average assumptions: Expected return on plan assets 5.74 % 5.83 % — — Discount Rate 3.48 % 3.07 % 3.65 % 3.21 % Rate of compensation increase 1.74 % 1.73 % — —

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	The Company’s outstanding debt is as follows: (In millions) September 30, December 31, Short-term: Commercial paper $ 325 $ — Term loan facility 300 — Current portion of long-term debt 514 314 1,139 314 Long-term: Senior notes – 2.35% due 2019 — 300 Senior notes – 2.35% due 2020 500 499 Senior notes – 3.50% due 2020 698 — Senior notes – 4.80% due 2021 499 499 Senior notes - Floating rate due 2021 298 — Senior notes – 2.75% due 2022 498 497 Senior notes – 3.30% due 2023 348 348 Senior notes – 4.05% due 2023 249 249 Senior notes – 3.50% due 2024 597 597 Senior notes – 3.875% due 2024 993 — Senior notes – 3.50% due 2025 497 496 Senior notes – 1.349% due 2026 603 — Senior notes – 3.75% due 2026 597 596 Senior notes – 4.375% due 2029 1,499 — Senior notes – 1.979% due 2030 602 — Senior notes – 5.875% due 2033 298 297 Senior notes – 4.75% due 2039 494 — Senior notes – 4.35% due 2047 492 492 Senior notes – 4.20% due 2048 592 592 Senior notes – 4.90% due 2049 1,237 — Mortgage – 5.70% due 2035 347 358 Other 5 4 11,943 5,824 Less current portion 514 314 $ 11,429 $ 5,510
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. September 30, 2019 December 31, 2018 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Short-term debt $ 1,139 $ 1,140 $ 314 $ 313 Long-term debt $ 11,429 $ 12,666 $ 5,510 $ 5,437

Restructuring Costs (Tables)

Restructuring Costs (Tables)	9 Months Ended
	Sep. 30, 2019
Restructuring and Related Activities [Abstract]
Restructuring Activities	Details of the JLT integration and restructuring activity from January 1, 2019 through September 30, 2019 , 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 92 21 9 70 192 Cash payments (59 ) (5 ) (9 ) (70 ) (143 ) Non-cash charges — (7 ) — — (7 ) Liability at 9/30/19 $ 33 $ 9 $ — $ — $ 42 (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. Details of the other restructuring activity from January 1, 2018 through September 30, 2019 , which includes liabilities from actions prior to 2019 , are as follows: (In millions) Liability at 1/1/18 Amounts Accrued Cash Paid Other Liability at 12/31/18 Amounts Accrued Cash Paid Other Liability at 9/30/19 Severance $ 15 $ 137 $ (77 ) $ (2 ) $ 73 $ 44 $ (95 ) $ (4 ) $ 18 Future rent under non-cancelable leases and other costs 50 24 (37 ) 2 39 12 (13 ) (6 ) $ 32 Total $ 65 $ 161 $ (114 ) $ — $ 112 $ 56 $ (108 ) $ (10 ) $ 50

Segment Information (Tables)

Segment Information (Tables)	9 Months Ended
	Sep. 30, 2019
Segment Reporting [Abstract]
Selected Information And Details For MMC's Operating Segments	Selected information about the Company’s operating segments for the three -and nine -month periods ended September 30, 2019 and 2018 are as follows: Three Months Ended September 30, Nine Months Ended (In millions) Revenue Operating Income (Loss) Revenue Operating Income (Loss) 2019– Risk and Insurance Services $ 2,206 (a) $ 218 $ 7,203 (c) $ 1,468 Consulting 1,785 (b) 317 5,258 (d) 874 Total Operating Segments 3,991 535 12,461 2,342 Corporate/Eliminations (23 ) (68 ) (73 ) (257 ) Total Consolidated $ 3,968 $ 467 $ 12,388 $ 2,085 2018– Risk and Insurance Services $ 1,863 (a) $ 293 $ 6,303 (c) $ 1,481 Consulting 1,656 (b) 291 4,974 (d) 805 Total Operating Segments 3,519 584 11,277 2,286 Corporate/Eliminations (15 ) (43 ) (39 ) (146 ) Total Consolidated $ 3,504 $ 541 $ 11,238 $ 2,140 (a) Includes inter-segment revenue of $3 million and $4 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $31 million and $18 million in 2019 and 2018 , respectively, and equity method income of $10 million and $4 million in 2019 and 2018 , respectively and $51 million related to the sale of business in 2018 . (b) Includes inter-segment revenue of $20 million and $11 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $1 million in 2018 , and equity method income of $4 million in 2018 . (c) Includes inter-segment revenue of $7 million and $5 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $80 million and $46 million in 2019 and 2018 , respectively, and equity method income of $16 million and $10 million in 2019 and 2018 , respectively and $51 million related to the sale of business in 2018 . (d) Includes inter-segment revenue of $66 million and $34 million in 2019 and 2018 , respectively, interest income on fiduciary funds of $2 million and $3 million in 2019 and 2018 , respectively and equity method income of $10 million and $12 million in 2019 and in 2018 , respectively.
Details of Operating Segment Revenue	Details of operating segment revenue for the three and nine -month periods ended September 30, 2019 and 2018 are as follows: Three Months Ended September 30, Nine Months Ended (In millions) 2019 2018 2019 2018 Risk and Insurance Services Marsh $ 1,923 $ 1,643 $ 5,850 $ 5,106 Guy Carpenter 283 220 1,353 1,197 Total Risk and Insurance Services 2,206 1,863 7,203 6,303 Consulting Mercer 1,280 1,175 3,695 3,504 Oliver Wyman Group 505 481 1,563 1,470 Total Consulting 1,785 1,656 5,258 4,974 Total Operating Segments 3,991 3,519 12,461 11,277 Corporate / Eliminations (23 ) (15 ) (73 ) (39 ) Total $ 3,968 $ 3,504 $ 12,388 $ 11,238

Nature of Operations (Details)

Nature of Operations (Details)	Mar. 31, 2019countrysegment	Sep. 30, 2019segment
Nature of Operations [Line Items]
Number of business segments (segment)		2
Jardine Lloyd Thompson Group plc
Nature of Operations [Line Items]
Number of business segments (segment)	3
Number of countries in which entity operates (country) | country	41

Principles of Consolidation A_3

Principles of Consolidation And Other Matters (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jan. 01, 2019	Dec. 31, 2018
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 193,000,000		$ 193,000,000			$ 186,000,000
Equity method investments lag period			3 months
Gain (loss) on investment income, net	7,000,000	$ (52,000,000)	$ 20,000,000	$ (24,000,000)
Gains on equity securities	4,000,000	25,000,000	10,000,000	43,000,000
Equity method income	3,000,000	$ 4,000,000	10,000,000	$ 14,000,000
Operating lease, liability	2,298,000,000		2,298,000,000
Operating lease, right-of-use asset	$ 1,957,000,000		$ 1,957,000,000			0
Effective tax rate (as a percent)	26.00%	27.50%	27.80%	25.20%
Unrecognized tax benefits	$ 76,000,000		$ 76,000,000			$ 78,000,000
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	$ 7,000,000		$ 7,000,000
Accounting Standards Update 2016-02
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating lease, liability					$ 1,900,000,000
Operating lease, right-of-use asset					1,700,000,000
Restatement Adjustment | Accounting Standards Update 2016-02
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Other liabilities					$ 200,000,000
Alexander Forbes Group Holdings Limited
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Equity method investment other than temporary impairment charge		$ 81,000,000		$ 81,000,000

Revenue - Narrative (Details)

Revenue - Narrative (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Percentage of total revenue		1.00%
Increases as a result of cumulative catch-up adjustments arising from changes in the estimate of the stage of completion, excluding amounts transferred to receivables during the period		$ 353
Transferred to receivables from contract assets		262
Cash received for performance obligations not yet fulfilled		400
Revenue recognized that was included in the contract liability balance at the beginning of the period		$ 378
Performance obligation satisfied in previous period	$ 67
Mercer Consulting Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Consulting revenue, payment terms (in days)		30 days
Revenue, remaining performance obligation	127	$ 127
Oliver Wyman Group Consulting Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation	2	2
Guy Carpenter Reinsurance Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Contract with customer, liability, adjustment	17
Marsh Insurance Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation	$ 33	$ 33
Risk and Insurance Services Segment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Insurance brokerage commissions, payment terms (in days)		30 days
Health Brokerage and Consulting
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer, percent		63.00%
Minimum | Oliver Wyman Group Consulting Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Consulting revenue, payment terms (in days)		30 days
Minimum | Risk and Insurance Services Segment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated brokerage revenue, payment terms (in months)		12 months
Reinsurance brokerage revenue, payment terms (in months)		12 months
Maximum | Oliver Wyman Group Consulting Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Consulting revenue, payment terms (in days)		60 days
Maximum | Risk and Insurance Services Segment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Estimated brokerage revenue, payment terms (in months)		18 months
Reinsurance brokerage revenue, payment terms (in months)		18 months
Jardine Lloyd Thompson Group plc
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Increase for contract acquired in business combination		$ 58
Increase for contract acquired in business combination		$ 45

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 2,206	$ 7,203
Fiduciary interest income	31	80
Risk and Insurance Services Segment | EMEA
Disaggregation of Revenue [Line Items]
Revenue	536	1,821
Risk and Insurance Services Segment | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	242	698
Risk and Insurance Services Segment | Latin America
Disaggregation of Revenue [Line Items]
Revenue	110	304
Risk and Insurance Services Segment | Total International
Disaggregation of Revenue [Line Items]
Revenue	888	2,823
Risk and Insurance Services Segment | U.S./Canada
Disaggregation of Revenue [Line Items]
Revenue	1,014	2,972
Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,785	5,258
Wealth | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	592	1,748
Health | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	441	1,341
Career | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	247	606
Marsh Insurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	1,902	5,795
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	273	1,328
Marsh & Guy Carpenter | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	2,175	7,123
Mercer Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,280	3,695
Oliver Wyman Group Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 505	$ 1,563

Revenue - Contract Assets and C

Revenue - Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019
Revenue from Contract with Customer [Abstract]
Contract Assets	$ 240	$ 112
Contract Liabilities	$ 611	$ 545

Revenue - Estimated Revenue Exp

Revenue - Estimated Revenue Expected to Be Recognized Related to Performance Obligations (Details) $ in Millions	Sep. 30, 2019USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 107
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)	1 year
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	$ 41
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	$ 10
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	$ 1
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	$ 3
Revenue, remaining performance obligation, expected timing of satisfaction, period (in years)

Fiduciary Assets and Liabilit_2

Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 9,600		$ 9,600		$ 7,300
Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	31		80
Operating Segments | Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	31	$ 18	80	$ 46
Operating Segments | Consulting Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds	$ 1	$ 1	$ 2	$ 3

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net income before non-controlling interests	$ 306	$ 279	$ 1,377	$ 1,511
Less: Net income attributable to non-controlling interests	3	3	26	14
Net income attributable to the Company	$ 303	$ 276	$ 1,351	$ 1,497
Basic weighted average common shares outstanding (in shares)	506	504	506	506
Dilutive effect of potentially issuable common shares (in shares)	5	6	5	6
Diluted weighted average common shares outstanding (in shares)	511	510	511	512
Average stock price used to calculate common stock equivalents (in dollars per share)	$ 99.97	$ 84.68	$ 94.75	$ 83.05

Supplemental Disclosures to t_3

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Additional Information Concerning Acquisitions, Interest And Income Taxes Paid) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Supplemental Cash Flow Information [Abstract]
Assets acquired, excluding cash	$ 8,619	$ 679
Liabilities assumed	(2,758)	(35)
Non-controlling interests assumed	(295)	0
Contingent/deferred purchase consideration	(66)	(108)
Net cash outflow for current year acquisitions	5,500	536
Interest paid	387	225
Income taxes paid, net of refunds	$ 442	$ 455

Supplemental Disclosures to t_4

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Mar. 31, 2019	Sep. 30, 2019	Sep. 30, 2018
Supplemental Cash Flow Information [Abstract]
Deferred and contingent consideration from prior years acquisition		$ 60	$ 106
Deferred purchase consideration from prior years' acquisitions		37	59
Contingent consideration from prior year's acquisitions		23	47
Net charge for adjustments related to acquisition related accounts		26	19
Payment of contingent consideration		35	29
Non-cash issuance of common stock		164	129
Stock-based compensation expense, equity awards		$ 184	$ 146
Right-of-use asset, noncash	$ 1,700
Right-to-use liability, noncash	$ 1,900

Other Comprehensive Income (L_3

Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Cumulative effect of amended accounting standard					$ (14)
Other comprehensive income before reclassifications	$ (419)	$ (255)	$ (340)	$ (519)
Amounts reclassified from accumulated other comprehensive income	15	32	56	88
Other comprehensive income (loss), net of tax	(404)	(223)	(284)	(431)
AOCI Attributable to Parent
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(4,527)	(4,265)	(4,647)	(4,043)
Other comprehensive income (loss), net of tax	(404)	(223)	(284)	(431)
Balance, ending of period	(4,931)	(4,488)	(4,931)	(4,488)
Unrealized Investment Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	0	0	0	14
Cumulative effect of amended accounting standard					(14)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	0	0	0	0
Balance, ending of period	0	0	0	0
Pension/Post-Retirement Plans Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(2,942)	(2,807)	(2,953)	(2,892)
Cumulative effect of amended accounting standard					0
Other comprehensive income before reclassifications	56	(13)	26	16
Amounts reclassified from accumulated other comprehensive income	15	32	56	88
Other comprehensive income (loss), net of tax	71	19	82	104
Balance, ending of period	(2,871)	(2,788)	(2,871)	(2,788)
Foreign Currency Translation Gains (Losses)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance, beginning of period	(1,585)	(1,458)	(1,694)	(1,165)
Cumulative effect of amended accounting standard					$ 0
Other comprehensive income before reclassifications	(475)	(242)	(366)	(535)
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive income (loss), net of tax	(475)	(242)	(366)	(535)
Balance, ending of period	$ (2,060)	$ (1,700)	$ (2,060)	$ (1,700)

Other Comprehensive Income (L_4

Other Comprehensive Income (Loss) (Schedule Of Components Of Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Equity [Abstract]
Foreign currency translation adjustments, Pre-Tax	$ (475)	$ (237)	$ (366)	$ (538)
Foreign currency translation adjustments, Tax	0	5	0	(3)
Foreign currency translation adjustments, Net of Tax	(475)	(242)	(366)	(535)
Pension/post-retirement plans:
Prior services credits, Pre-Tax	(1)	(1)	(2)	(3)
Prior service credits, Tax	(1)	(1)	(1)	(1)
Prior service credits, Net of Tax	0	0	(1)	(2)
Net actuarial loss, Pre-Tax	25	36	77	110
Net actuarial loss, Tax	6	7	18	23
Net actuarial loss, Net of Tax	19	29	59	87
Effect of remeasurements, Pre-Tax	(8)	3	(9)	3
Effect of remeasurements, Tax	(2)	0	(2)	0
Effect of remeasurements, Net of Tax	(6)	3	(7)	3
Effect of settlement, Pre-tax	2	0	6	0
Effect of settlement, Tax	0	0	1	0
Effect of settlement, Net of Tax	2	0	5	0
Subtotal, Pre-Tax	18	38	72	110
Subtotal, Tax	3	6	16	22
Subtotal, Net of Tax	15	32	56	88
Foreign currency translation adjustment, Pre-Tax	64	(15)	30	21
Foreign currency translation adjustment, Tax	8	(2)	4	5
Foreign currency translation adjustment, Net of Tax	56	(13)	26	16
Pension/post-retirement plans (losses) gains, Pre-Tax	82	23	102	131
Pension/post-retirement plans (losses) gains, Tax	11	4	20	27
Pension/post-retirement plans (losses) gains, Net of Tax	71	19	82	104
Other comprehensive (loss), before tax	(393)	(214)	(264)	(407)
Other comprehensive (loss) income, Tax	11	9	20	24
Other comprehensive income (loss), net of tax	$ (404)	$ (223)	$ (284)	$ (431)

Acquisitions and Dispositions_2

Acquisitions and Dispositions (Narrative) (Details) £ / shares in Units, colleague in Thousands, $ in Millions, £ in Billions	Jun. 01, 2019USD ($)	Apr. 01, 2019USD ($)	Apr. 01, 2019GBP (£)colleague£ / shares	Sep. 20, 2018GBP (£)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)acquisition	Sep. 30, 2018USD ($)	Dec. 31, 2018acquisition	Jan. 01, 2019
Business Acquisition [Line Items]
Assumption of debt								$ 2,758	$ 35
Total consideration								5,925	661
Cash								5,859	553
Estimated fair value of deferred/contingent consideration								66	108
Deferred purchase consideration from prior years' acquisitions								37	59
Contingent consideration from prior year's acquisitions								23	47
Amortization of intangible assets								235	135
Payments to acquire outstanding minority interests of subsidiaries								91	0
Increase (decrease) in costs					$ (4)			(173)	662
Jardine Lloyd Thompson Group plc
Business Acquisition [Line Items]
Business acquisition, share price (in gbp per share) | £ / shares			£ 19.15
Equity interests issued and issuable		$ 5,600	£ 4.3
Assumption of debt		$ 1,000
Entity number of employees | colleague			10
Total consideration				£ 5.2				5,568
Cash								5,568
Estimated fair value of deferred/contingent consideration								0
Adjustments to intangible assets					(50)
Goodwill, purchase accounting adjustments					65
Business combination, acquisition related costs					4			99
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions								37	59
Contingent consideration from prior year's acquisitions								58	76
Payments to acquire outstanding minority interests of subsidiaries							$ 75
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration								5,925
Cash								5,859
Estimated fair value of deferred/contingent consideration								66
Revenue related to acquisitions					352	$ 36		848	50
Operating (loss) income related to acquisitions					(69)	$ (5)		$ (51)	$ (7)
Risk and Insurance Services Segment
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition								4		12
Consulting Segment
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition										8
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)								2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)								4 years
Marsh India
Business Acquisition [Line Items]
Percentage of ownership in equity investment										26.00%	49.00%
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
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
Adjustment | Jardine Lloyd Thompson Group plc
Business Acquisition [Line Items]
Amortization of intangible assets					$ (4)

Acquisitions and Dispositions_3

Acquisitions and Dispositions (Allocation Of Acquisition Costs) (Details) $ in Millions, £ in Billions	Sep. 20, 2018GBP (£)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Apr. 01, 2019USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Cash		$ 5,859	$ 553
Estimated fair value of deferred/contingent consideration		66	108
Total consideration		5,925	661
Allocation of purchase price:
Goodwill		14,286	$ 9,435		$ 9,599	$ 9,089
Jardine Lloyd Thompson Group plc
Business Acquisition [Line Items]
Cash		5,568
Estimated fair value of deferred/contingent consideration		0
Total consideration	£ 5.2	5,568
Allocation of purchase price:
Cash and cash equivalents		353
Accounts receivable, net		714
Other current assets		143
Fixed assets, net		89
Other intangible assets		1,613
Goodwill		4,761
Right of use assets		382
Deferred tax assets		65
Other assets		493
Total assets acquired		8,613
Current liabilities		689
Fiduciary liabilities		1,275
Less- fiduciary assets		(1,275)
Long-term debt		1,044		$ 1,000
Long-term lease liability		389
Pension, post-retirement and post-employment liabilities		248
Liabilities for errors and omissions		31
Other liabilities		349
Total liabilities assumed		2,750
Non controlling interests		295
Net assets acquired		5,568
Other
Business Acquisition [Line Items]
Cash		291
Estimated fair value of deferred/contingent consideration		66
Total consideration		357
Allocation of purchase price:
Cash and cash equivalents		6
Accounts receivable, net		5
Other current assets		0
Fixed assets, net		2
Other intangible assets		143
Goodwill		201
Right of use assets		0
Deferred tax assets		0
Other assets		8
Total assets acquired		365
Current liabilities		5
Fiduciary liabilities		0
Less- fiduciary assets		0
Long-term debt		0
Long-term lease liability		0
Pension, post-retirement and post-employment liabilities		0
Liabilities for errors and omissions		0
Other liabilities		3
Total liabilities assumed		8
Non controlling interests		0
Net assets acquired		357
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash		5,859
Estimated fair value of deferred/contingent consideration		66
Total consideration		5,925
Allocation of purchase price:
Cash and cash equivalents		359
Accounts receivable, net		719
Other current assets		143
Fixed assets, net		91
Other intangible assets		1,756
Goodwill		4,962
Right of use assets		382
Deferred tax assets		65
Other assets		501
Total assets acquired		8,978
Current liabilities		694
Fiduciary liabilities		1,275
Less- fiduciary assets		(1,275)
Long-term debt		1,044
Long-term lease liability		389
Pension, post-retirement and post-employment liabilities		248
Liabilities for errors and omissions		31
Other liabilities		352
Total liabilities assumed		2,758
Non controlling interests		295
Net assets acquired		$ 5,925

Acquisitions and Dispositions_4

Acquisitions and Dispositions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2019USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 1,756
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	1,647
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	109
Jardine Lloyd Thompson Group plc
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	1,613
Jardine Lloyd Thompson Group plc | Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 1,511
Finite-lived intangible assets, remaining amortization period	13 years
Jardine Lloyd Thompson Group plc | Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 102
Finite-lived intangible assets, remaining amortization period	4 years
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 143
Other | Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 136
Finite-lived intangible assets, remaining amortization period	12 years
Other | Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 7
Finite-lived intangible assets, remaining amortization period	3 years

Acquisitions and Dispositions_5

Acquisitions and Dispositions (Pro-Forma Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Business Combinations [Abstract]
Revenue	$ 3,967	$ 3,940	$ 12,830	$ 12,842
Net income attributable to the Company	$ 306	$ 181	$ 1,445	$ 804
Basic net income per share attributable to the Company (in dollars per share)	$ 0.61	$ 0.36	$ 2.85	$ 1.59
Diluted net income per share attributable to the Company (in dollars per share)	$ 0.60	$ 0.36	$ 2.83	$ 1.57

Goodwill and Other Intangible_2

Goodwill and Other Intangibles (Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Goodwill [Roll Forward]
Balance as of January 1,	$ 9,599	$ 9,089
Goodwill acquired	4,962	410
Other adjustments	(275)	(64)
Balance at September 30,	$ 14,286	$ 9,435

Goodwill and Other Intangible_3

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill acquired	$ 4,962	$ 410
Goodwill	14,286	9,435	$ 9,599	$ 9,089
Aggregate amortization expense	235	$ 135
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill acquired	201
Goodwill	11,300
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	3,000
Jardine Lloyd Thompson Group plc
Segment Reporting Information [Line Items]
Goodwill acquired	4,800
Goodwill	$ 4,761

Goodwill and Other Intangible_4

Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Cost	$ 3,890	$ 2,229
Accumulated Amortization	1,021	792
Net Carrying Amount	2,869	1,437
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost	3,526	1,970
Accumulated Amortization	824	639
Net Carrying Amount	2,702	1,331
Other
Finite-Lived Intangible Assets [Line Items]
Gross Cost	364	259
Accumulated Amortization	197	153
Net Carrying Amount	$ 167	$ 106

Goodwill And Other Intangible_5

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
2019 (excludes amortization through September 30, 2019)	$ 95
2020	354
2021	343
2022	327
2023	320
Subsequent years	1,430
Net Carrying Amount	$ 2,869	$ 1,437

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) $ / shares in Units, shares in Millions, $ in Millions	1 Months Ended		3 Months Ended				9 Months Ended
	Apr. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Sep. 30, 2019USD ($)$ / sharesshares	Jun. 30, 2019USD ($)	Mar. 31, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)$ / sharesshares	Sep. 30, 2018USD ($)	Sep. 30, 2019R / shares	Dec. 31, 2018USD ($)	Sep. 30, 2018R / shares	Dec. 31, 2014R / shares
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Net charge for adjustments related to acquisition related accounts							$ 26	$ 19
Increase in fair value of contingent consideration due to 5% increase in projections							46
Decrease in fair value of contingent consideration due to 5% decrease in projections							39
Carrying value of investment			$ 452				452			$ 287
Equity method income			3			$ 4	10	14
Equity securities			19				19			146
Gains on equity securities			4			25	10	43
Equity investments without readily determinable market value			47				$ 47			75
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			219				$ 219			61
Private Equity Funds, Non-US
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment			95				95			82
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) | R / shares									R 5.6		R 4.95	R 7.50
Carrying value of investment			$ 138				$ 138
Percentage of ownership in equity investment			33.00%				33.00%
Other than temporary impairment						$ 81		$ 81
Shares owned in investment (in shares) | shares			443				443
Equity method investment, quoted market value			$ 166				$ 166
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
Treasury Lock | Jardine Lloyd Thompson Group plc
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Derivative hedges, assets										2,000
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) | $ / shares			$ 1				$ 1
Fair Value, Measurements, Recurring | Other Assets
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent purchase consideration asset			$ 65				$ 65			0
Equity securities			5				5			133
Fair Value, Measurements, Recurring | Other Assets | Unobservable Inputs (Level 3)
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Contingent purchase consideration asset			65				65			0
Equity securities			$ 0				$ 0			$ 0

Fair Value Measurements (Assets

Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Financial instruments owned:
Exchange traded equity securities	$ 19	$ 146
Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	272	410
Fiduciary Assets:
Fiduciary assets	433	100
Liabilities:
Total liabilities measured at fair value	185	624
Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	199	402
Fiduciary Assets:
Fiduciary assets	433	100
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	116
Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Financial instruments owned:
Total assets measured at fair value	65	0
Fiduciary Assets:
Fiduciary assets	0	0
Liabilities:
Total liabilities measured at fair value	185	508
US Treasury Bills | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	20
US Treasury Bills | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	0	20
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	433	80
Money Market Funds | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Fiduciary Assets:
Fiduciary assets	433	80
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
Forward Contracts | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contracts	0	441
Forward Contracts | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contracts	0	0
Forward Contracts | Observable Inputs (Level 2) | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contracts	0	116
Forward Contracts | Unobservable Inputs (Level 3) | Fair Value, Measurements, Recurring
Liabilities:
Acquisition related derivative contracts	0	325
Other Assets | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	5	133
Mutual funds	157	151
Other equity investments	8	8
Contingent purchase consideration asset	65	0
Other Assets | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Exchange traded equity securities	5	133
Mutual funds	157	151
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	65	0
Cash and Cash Equivalents | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	37	118
Cash and Cash Equivalents | Identical Assets (Level 1) | Fair Value, Measurements, Recurring
Financial instruments owned:
Money market funds	37	118
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	185	183
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	$ 185	$ 183

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Revaluation Impact			$ 26	$ 19
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period,	$ 196	$ 185	508	189
(Reductions) Additions	(7)
(Reductions) Additions		8	33	34
Payments	(13)	(35)	(58)	(76)
Revaluation Impact	6	8	26	19
Other	3	2	1	2
Balance at September 30,	185	268	185	268
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	$ 100	$ (325)	$ 100

Derivatives - Narrative (Detail

Derivatives - Narrative (Details) £ in Billions	Sep. 20, 2018GBP (£)	Jan. 31, 2019USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Dec. 31, 2018USD ($)	Mar. 31, 2019EUR (€)
Derivative [Line Items]
Total consideration			$ 5,925,000,000	$ 661,000,000
Decrease in net investment hedges			39,000,000
Foreign Exchange Forward
Derivative [Line Items]
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		5,568,000,000
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
Unrealized loss					$ 116,000,000
Senior Notes
Derivative [Line Items]
Debt instrument face amount		$ 5,000,000,000
Senior Notes | Jardine Lloyd Thompson Group plc
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%

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Lessee, Lease, Description [Line Items]
Percentage of lease obligations used for office space		98.00%
Lessee, operating lease, lease not yet commenced, amount	$ 71	$ 71
Lessee, operating lease, lease not yet commenced, term (years)	12 months	12 months
Operating lease, right-of-use asset	$ 1,957	$ 1,957		$ 0
Operating lease, liability	2,298	2,298
Operating lease, impairment loss	$ 7	$ 7
Minimum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (years)	10 years	10 years
Maximum
Lessee, Lease, Description [Line Items]
Lessee, operating lease, term of contract (years)	25 years	25 years
Jardine Lloyd Thompson Group plc
Lessee, Lease, Description [Line Items]
Operating lease, right-of-use asset			$ 400
Operating lease, liability			$ 400

Leases - Lease Cost and Additio

Leases - Lease Cost and Additional Information (Details) $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2019USD ($)
Lessee, Lease, Description [Line Items]
Operating lease cost	$ 94	$ 276
Short-term lease cost	4	7
Variable lease cost	37	113
Sublease income	(4)	(12)
Net lease cost	$ 131	384
Operating cash outflows from operating leases		288
Right of use assets obtained in exchange for new operating lease liabilities		$ 112
Real Estate Lease
Lessee, Lease, Description [Line Items]
Weighted-average remaining lease term	8 years 10 months 9 days	8 years 10 months 9 days
Weighted-average discount rate	3.09%	3.09%

Leases - Future Minimum Payment

Leases - Future Minimum Payments for Operating Leases (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Leases [Abstract]
Remainder of 2019	$ 104
2020	406
2021	348
2022	324
2023	279
2024	233
Subsequent years	940
Total future lease payments	2,634
Less: Imputed interest	(336)
Total	2,298
Current lease liabilities	341	$ 0
Long-term lease liabilities	$ 1,957	$ 0

Leases - Aggregate Fixed Future

Leases - Aggregate Fixed Future Minimum Commitments (Details) $ in Millions	Dec. 31, 2018USD ($)
Gross Rental Commitments
2019, Gross Rental Commitments	$ 361
2020, Gross Rental Commitments	340
2021, Gross Rental Commitments	277
2022, Gross Rental Commitments	252
2023, Gross Rental Commitments	214
Subsequent years, Gross Rental Commitments	753
Rentals from Subleases
2019, Rentals from Subleases	32
2020, Rentals from Subleases	31
2021, Rentals from Subleases	12
2022, Rentals from Subleases	10
2023, Rentals from Subleases	9
Subsequent years, Rentals from Subleases	32
Net Rental Commitments
2019, Net Rental Commitments	329
2020, Net Rental Commitments	309
2021 Net Rental Commitments	265
2022, Net Rental Commitments	242
2023, Net Rental Commitments	205
Subsequent years, Net Rental Commitments	$ 721

Retirement Benefits (Narrative)

Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Mar. 31, 2019
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 85
Estimated future employer contributions in current fiscal year	32
Jardine Lloyd Thompson Group plc
Defined Benefit Plan Disclosure [Line Items]
Pension, post-retirement and post-employment liabilities				$ 248
Pension, post-retirement and post-employment plan assets				$ 700
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 106	$ 100
United States | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	64.00%
Actual asset allocation percentage of equity	62.00%
United States | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	36.00%
Actual asset allocation percentage of equity	38.00%
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 74	$ 61
United Kingdom | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	36.00%
Actual asset allocation percentage of equity	33.00%
United Kingdom | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	64.00%
Actual asset allocation percentage of equity	67.00%
United Kingdom | Geographic Concentration Risk | Non-U.S. Plans
Defined Benefit Plan Disclosure [Line Items]
Concentration risk percentage			81.00%

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 10	$ 8	$ 28	$ 25
Interest cost	120	114	360	349
Expected return on plan assets	(214)	(213)	(644)	(652)
Amortization of prior service credit	0	0	0	(1)
Recognized actuarial loss	25	36	77	110
Net periodic benefit (credit) cost	(59)	(55)	(179)	(169)
Settlement loss			4	0
Total (credit) cost	(59)	(55)	(175)	(169)
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	0	1
Interest cost	1	0	2	2
Expected return on plan assets	0	0	0	0
Amortization of prior service credit	0	(1)	(1)	(3)
Recognized actuarial loss	(1)	1	(1)	1
Net periodic benefit (credit) cost	0	1	0	1
Settlement loss			0	0
Total (credit) cost	0	1	0	1
United States | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	61	58	181	176
Expected return on plan assets	(86)	(89)	(257)	(268)
Amortization of prior service credit			0	0
Recognized actuarial loss	11	14	33	41
Net periodic benefit (credit) cost	(14)	(17)	(43)	(51)
United States | Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Interest cost	1	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service credit			0	(1)
Recognized actuarial loss	(1)	0	(1)	0
Net periodic benefit (credit) cost	0	0	0	0
Foreign Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	10	8	28	25
Interest cost	59	56	179	173
Expected return on plan assets	(128)	(124)	(387)	(384)
Amortization of prior service credit	0	0	0	(1)
Recognized actuarial loss	14	22	44	69
Net periodic benefit (credit) cost	(45)	(38)	(136)	(118)
Settlement loss			4	0
Total (credit) cost			(132)	(118)
Foreign Plan | Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	1	0	1
Interest cost	0	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service credit	0	(1)	(1)	(2)
Recognized actuarial loss	0	1	0	1
Net periodic benefit (credit) cost	$ 0	$ 1	0	1
Settlement loss			0	0
Total (credit) cost			$ 0	$ 1

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		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	$ (467)	$ (541)	$ (2,085)	$ (2,140)
Other net benefit (credits) cost	(69)	(63)	(203)	(194)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	10	8	28	25
Other net benefit (credits) cost	(69)	(63)	(203)	(194)
Total (credit) cost	(59)	(55)	(175)	(169)
Post-retirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	0	1	0	1
Other net benefit (credits) cost	0	0	0	0
Total (credit) cost	$ 0	$ 1	$ 0	$ 1

Retirement Benefits (Schedule_3

Retirement Benefits (Schedule Of Defined Benefit Plan Weighted Average Assumption Used In Calculating Net Periodic Benefit Cost) (Details)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Pension Benefits
Weighted average assumptions:
Expected return on plan assets	5.74%	5.83%
Discount Rate	3.48%	3.07%
Rate of compensation increase	1.74%	1.73%
Post-retirement Benefits
Weighted average assumptions:
Expected return on plan assets	0.00%	0.00%
Discount Rate	3.65%	3.21%
Rate of compensation increase	0.00%	0.00%

Debt (Schedule Of Outstanding D

Debt (Schedule Of Outstanding Debt) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018	Mar. 31, 2018
Debt Instrument [Line Items]
Short-term: Commercial paper	$ 325	$ 0
Current portion of long-term debt	514	314
Short-term debt	1,139	314
Long-term debt	11,943	5,824
Long-term debt, net	11,429	5,510
Term Loan Facility
Debt Instrument [Line Items]
Short-term: Term loan facility	300	0
2.35% Senior Debt Obligations Due 2019
Debt Instrument [Line Items]
Long-term debt	$ 0	300
Interest rate	2.35%
2.35% Senior Debt Obligations Due 2020
Debt Instrument [Line Items]
Long-term debt	$ 500	499
Interest rate	2.35%
3.50% Senior Debt Obligations Due 2020
Debt Instrument [Line Items]
Long-term debt	$ 698	0
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	$ 298	0
2.75% Senior Debt Obligations Due 2022
Debt Instrument [Line Items]
Long-term debt	$ 498	497
Interest rate	2.75%
3.30% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Long-term debt	$ 348	348
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	$ 597	597
Interest rate	3.50%
3.875% Senior Debt Obligations Due 2024
Debt Instrument [Line Items]
Long-term debt	$ 993	0
Interest rate	3.875%
3.50% Senior Debt Obligations Due 2025
Debt Instrument [Line Items]
Long-term debt	$ 497	496
Interest rate	3.50%
1.349% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 603	0
Interest rate	1.349%
3.75% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt	$ 597	596
Interest rate	3.75%
4.375% Senior Debt Obligations Due 2029
Debt Instrument [Line Items]
Long-term debt	$ 1,499	0
Interest rate	4.375%
1.979% Senior Debt Obligations Due 2030
Debt Instrument [Line Items]
Long-term debt	$ 602	0
Interest rate	1.979%
5.875% Senior Debt Obligations Due 2033
Debt Instrument [Line Items]
Long-term debt	$ 298	297
Interest rate	5.875%
4.75% Senior Debt Obligations Due 2039
Debt Instrument [Line Items]
Long-term debt	$ 494	0
Interest rate	4.75%
4.35% Senior Debt Obligation Due 2047
Debt Instrument [Line Items]
Long-term debt	$ 492	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%		4.20%
4.90% Senior Debt Obligations Due 2049
Debt Instrument [Line Items]
Long-term debt	$ 1,237	0
Interest rate	4.90%
5.70% Mortgage Due 2035
Debt Instrument [Line Items]
Long-term debt	$ 347	358
Interest rate	5.70%
Other
Debt Instrument [Line Items]
Long-term debt	$ 5	$ 4

Debt (Narrative) (Details)

Debt (Narrative) (Details) £ in Billions

1 Months Ended

3 Months Ended

9 Months Ended

12 Months Ended

Sep. 30, 2019USD ($)

Aug. 31, 2019USD ($)

Jun. 30, 2019USD ($)

Apr. 30, 2019USD ($)

Mar. 31, 2019USD ($)

Oct. 31, 2018

Jun. 30, 2019USD ($)

Mar. 31, 2019USD ($)

Sep. 30, 2019USD ($)

Sep. 30, 2018USD ($)

Dec. 31, 2018USD ($)

Apr. 01, 2019USD ($)

Mar. 31, 2019EUR (€)

Jan. 31, 2019USD ($)

Oct. 01, 2018USD ($)

Sep. 18, 2018GBP (£)

Mar. 31, 2018USD ($)

Debt Instrument [Line Items]

Commercial paper outstanding

$ 325,000,000

$ 325,000,000

$ 0

Payments for early extinguishment of debt

585,000,000

$ 0

Financing Program

Debt Instrument [Line Items]

Debt financing program

$ 1,500,000,000

$ 1,500,000,000

1.349% Senior Debt Obligations Due 2026

Debt Instrument [Line Items]

Interest rate

1.349%

1.349%

1.979% Senior Debt Obligations Due 2030

Debt Instrument [Line Items]

Interest rate

1.979%

1.979%

Loan Facility One

Debt Instrument [Line Items]

Debt facilities, maximum borrowing capacity

$ 300,000,000

$ 300,000,000

Loan Facility Two

Debt Instrument [Line Items]

Revolving credit facility, amount outstanding

$ 300,000,000

300,000,000

4.20% Senior Debt Obligations Due 2048

Debt Instrument [Line Items]

Debt instrument face amount

$ 600,000,000

Interest rate

4.20%

4.20%

4.20%

Commercial Paper

Debt Instrument [Line Items]

Effective interest rate

2.29%

2.29%

Jardine Lloyd Thompson Group plc

Debt Instrument [Line Items]

Repayments of debt

$ 553,000,000

$ 450,000,000

Payments for early extinguishment of debt

$ 32,000,000

Debt assumed in acquisition

$ 1,044,000,000

$ 1,044,000,000

$ 1,000,000,000

Jardine Lloyd Thompson Group plc | Bridge Loan

Debt Instrument [Line Items]

Derivative, notional amount | £

£ 5.2

Payments of debt issuance costs

35,000,000

Amortization of debt issuance costs

$ 30,000,000

Interest expense, debt

$ 5,000,000

Senior Notes

Debt Instrument [Line Items]

Debt instrument face amount

$ 5,000,000,000

Repayments of debt

300,000,000

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 4.375% Due 2029

Debt Instrument [Line Items]

Debt instrument face amount

1,500,000,000

1,500,000,000

$ 1,250,000,000

Interest rate

4.375%

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 | 1.349% Senior Debt Obligations Due 2026

Debt Instrument [Line Items]

Debt instrument face amount | €

€ 550,000,000

Interest rate

1.349%

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%

1.979%

Senior Notes | Senior Debt Obligations 4.375% Due 2019

Debt Instrument [Line Items]

Debt instrument face amount

$ 250,000,000

$ 250,000,000

Senior Notes | Jardine Lloyd Thompson Group plc

Debt Instrument [Line Items]

Debt instrument face amount | €

€ 1,100,000,000

Term Loan Facility | Loan Facility One

Debt Instrument [Line Items]

Term of debt

1 year

Term Loan Facility | Loan Facility Two

Debt Instrument [Line Items]

Term of debt

3 years

3 years

Term Loan Facility | Loan Facilities Closed March 2019

Debt Instrument [Line Items]

Revolving credit facility, amount outstanding

$ 300,000,000

$ 300,000,000

Term of debt

1 year

Debt, average borrowing rate (percentage)

3.05%

3.05%

Term Loan Facility | Loan Facilities Canceled August 2019

Debt Instrument [Line Items]

Revolving credit facility, amount outstanding

$ 300,000,000

Revolving Credit Facility | Amended Revolving Credit Facility

Debt Instrument [Line Items]

Debt facilities, maximum borrowing capacity

$ 1,500,000,000

$ 1,800,000,000

Revolving credit facility, amount outstanding

$ 0

$ 0

Term of debt

5 years

Debt (Estimated Fair Value of S

Debt (Estimated Fair Value of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 1,139	$ 314
Long-term debt	11,429	5,510
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	1,140	313
Long-term debt	$ 12,666	$ 5,437

Restructuring Costs - Narrative

Restructuring Costs - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Dec. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring And related cost, period for expected cost		3 years
Amounts accrued		$ 56	$ 161
Jardine Lloyd Thompson Group plc
Restructuring Cost and Reserve [Line Items]
Amounts accrued		192
Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Restructuring and related cost, expected cost	$ 375	375
Restructuring and related cost, cost incurred to date	192	192
Amounts accrued	77
Risk and Insurance Services Segment | Severance and consulting costs
Restructuring Cost and Reserve [Line Items]
Amounts accrued		6
Risk and Insurance Services Segment | Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Amounts accrued	58	134
Consulting Segment | Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Amounts accrued	5	10
Corporate | Severance and future rent under non-cancelable leases and other costs
Restructuring Cost and Reserve [Line Items]
Amounts accrued		7
Corporate | Jardine Lloyd Thompson Group plc | Acquisition related
Restructuring Cost and Reserve [Line Items]
Amounts accrued	14	48
Mercer Consulting Group | Severance and consulting costs
Restructuring Cost and Reserve [Line Items]
Amounts accrued	$ 10	$ 43

Restructuring Costs (Restructur

Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Restructuring Reserve [Roll Forward]
Liability at beginning of period	$ 112	$ 65
Amounts Accrued	56	161
Cash Paid	(108)	(114)
Other	(10)	0
Liability at end of period	50	112
Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	73	15
Amounts Accrued	44	137
Cash Paid	(95)	(77)
Other	(4)	(2)
Liability at end of period	18	73
Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	39	50
Amounts Accrued	12	24
Cash Paid	(13)	(37)
Other	(6)	2
Liability at end of period	32	39
Jardine Lloyd Thompson Group plc
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0
Amounts Accrued	192
Cash Paid	(143)
Non-cash charges	(7)
Liability at end of period	42	0
Jardine Lloyd Thompson Group plc | Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0
Amounts Accrued	92
Cash Paid	(59)
Non-cash charges	0
Liability at end of period	33	0
Jardine Lloyd Thompson Group plc | Real estate related costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0
Amounts Accrued	21
Cash Paid	(5)
Non-cash charges	(7)
Liability at end of period	9	0
Jardine Lloyd Thompson Group plc | Information Technology
Restructuring Reserve [Roll Forward]
Liability at beginning of period	0
Amounts Accrued	9
Cash Paid	(9)
Non-cash charges	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
Amounts Accrued	70
Cash Paid	(70)
Non-cash charges	0
Liability at end of period	$ 0	$ 0

Common Stock (Details)

Common Stock (Details) - USD ($)	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Nov. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 300,000,000	$ 675,000,000
Stock-based compensation, shares issued during period	4,200,000	3,000,000
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	3,100,000	8,200,000
Payments for repurchase of common stock	$ 300,000,000	$ 675,000,000
Share repurchases program, authorized amount (up to)			$ 2,500,000,000
Stock repurchase program, remaining authorized repurchase amount	$ 566,000,000

Claims, Lawsuits And Other Co_2

Claims, Lawsuits And Other Contingencies (Details) $ in Millions	Sep. 30, 2019USD ($)	Sep. 30, 2019GBP (£)	Feb. 28, 2019USD ($)	Feb. 28, 2019GBP (£)
Loss Contingencies [Line Items]
Loss contingency, estimate of possible loss | $	$ 83
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			$ 49.2	£ 38,400,000

Segment Information - Narrative

Segment Information - Narrative (Details)	Mar. 31, 2019countrysegment	Sep. 30, 2019segment
Segment Reporting Information [Line Items]
Number of business segments (segment)		2
Jardine Lloyd Thompson Group plc
Segment Reporting Information [Line Items]
Number of business segments (segment)	3
Number of countries in which entity operates (country) | country	41

Segment Information (Selected I

Segment Information (Selected Information And Details For MMC's Operating Segments) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue	$ 3,968	$ 3,504	$ 12,388	$ 11,238
Operating Income (Loss)	467	541	2,085	2,140
Equity method income	3	4	10	14
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Interest on fiduciary funds	31		80
Operating Segments
Segment Reporting Information [Line Items]
Revenue	3,991	3,519	12,461	11,277
Operating Income (Loss)	535	584	2,342	2,286
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,206	1,863	7,203	6,303
Operating Income (Loss)	218	293	1,468	1,481
Interest on fiduciary funds	31	18	80	46
Equity method income	10	4	16	10
Proceeds from divestiture of businesses		51		51
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,785	1,656	5,258	4,974
Operating Income (Loss)	317	291	874	805
Interest on fiduciary funds	1	1	2	3
Equity method income		4	10	12
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	(23)	(15)	(73)	(39)
Operating Income (Loss)	(68)	(43)	(257)	(146)
Intersegment Eliminations | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	3	4	7	5
Intersegment Eliminations | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	$ 20	$ 11	$ 66	$ 34

Segment Information (Details of

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Revenue	$ 3,968	$ 3,504	$ 12,388	$ 11,238
Operating Segments
Segment Reporting Information [Line Items]
Revenue	3,991	3,519	12,461	11,277
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,206	1,863	7,203	6,303
Operating Segments | Risk and Insurance Services Segment | Marsh Insurance Group
Segment Reporting Information [Line Items]
Revenue	1,923	1,643	5,850	5,106
Operating Segments | Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group
Segment Reporting Information [Line Items]
Revenue	283	220	1,353	1,197
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,785	1,656	5,258	4,974
Operating Segments | Consulting Segment | Mercer Consulting Group
Segment Reporting Information [Line Items]
Revenue	1,280	1,175	3,695	3,504
Operating Segments | Consulting Segment | Oliver Wyman Group Consulting Group
Segment Reporting Information [Line Items]
Revenue	505	481	1,563	1,470
Corporate/Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (23)	$ (15)	$ (73)	$ (39)

New Accounting Guidance - Narra

New Accounting Guidance - Narrative (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability	$ 2,298
Operating lease, right-of-use asset	1,957		$ 0
Retained earnings	$ 14,811		14,347
Cumulative effect of new accounting principle in period of adoption					$ (14)
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption			$ 14
Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, liability		$ 1,900
Operating lease, right-of-use asset		1,700
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings				$ 364
Accounting Standards Update 2016-16 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption				$ (14)
Real Estate | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Operating lease, right-of-use asset		1,700
Restatement Adjustment | Accounting Standards Update 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Other liabilities		$ 200