Marsh & McLennan Companies (MMC) 10-Q 27 Jul 18 2018 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2018	Jul. 24, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	MARSH & MCLENNAN COMPANIES, INC.
Entity Central Index Key	62,709
Trading Symbol	MMC
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Jun. 30, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q2
Amendment Flag	false
Entity Common Stock, Shares Outstanding		504,979,546

Consolidated Statements of Inco

Consolidated Statements of Income (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Revenue	$ 3,734	$ 3,495	$ 7,734	$ 6,998
Expense:
Compensation and benefits	2,135	1,998	4,359	4,003
Other operating expenses	908	796	1,776	1,545
Operating expenses	3,043	2,794	6,135	5,548
Operating income	691	701	1,599	1,450
Other net benefit credits	65	63	131	123
Interest income	3	2	6	4
Interest expense	(68)	(60)	(129)	(118)
Investment income	28	5	28	5
Income before income taxes	719	711	1,635	1,464
Income tax expense	183	204	403	379
Net income before non-controlling interests	536	507	1,232	1,085
Less: Net income attributable to non-controlling interests	5	6	11	15
Net income attributable to the Company	$ 531	$ 501	$ 1,221	$ 1,070
Net Income Per Share Attributable to the Company:
Basic net income per share attributable to the Company (usd per share)	$ 1.05	$ 0.98	$ 2.41	$ 2.08
Diluted net income per share attributable to the Company (usd per share)	$ 1.04	$ 0.96	$ 2.38	$ 2.05
Average number of shares outstanding:
Average number of shares outstanding - Basic	507	514	507	514
Average number of shares outstanding - Diluted	512	520	513	521
Shares outstanding at June 30,	505	513	505	513

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Statement of Comprehensive Income [Abstract]
Net income before non-controlling interests	$ 536	$ 507	$ 1,232	$ 1,085
Other comprehensive (loss) income, before tax:
Foreign currency translation adjustments	(529)	290	(301)	525
Unrealized investment gains	0	24	0	19
Gain (loss) related to pension/post-retirement plans	192	(5)	108	28
Other comprehensive (loss) income, before tax	(337)	309	(193)	572
Income tax expense on other comprehensive income	23	13	15	20
Other comprehensive (loss) income, net of tax	(360)	296	(208)	552
Comprehensive income	176	803	1,024	1,637
Less: comprehensive income attributable to non-controlling interest	5	6	11	15
Comprehensive income attributable to the Company	$ 171	$ 797	$ 1,013	$ 1,622

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 1,036	$ 1,205
Receivables
Commissions and fees	4,288	3,777
Advanced premiums and claims	62	65
Other	367	401
Gross receivables	4,717	4,243
Less-allowance for doubtful accounts and cancellations	(116)	(110)
Net receivables	4,601	4,133
Other current assets	538	224
Total current assets	6,175	5,562
Goodwill	9,177	9,089
Other intangible assets	1,234	1,274
Fixed assets (net of accumulated depreciation and amortization of $1,857 at June 30, 2018 and $1,826 at December 31, 2017)	698	712
Pension related assets	1,808	1,693
Deferred tax assets	532	669
Other assets	1,535	1,430
Total assets	21,159	20,429
Current liabilities:
Short-term debt	439	262
Accounts payable and accrued liabilities	2,246	2,083
Accrued compensation and employee benefits	1,103	1,718
Accrued income taxes	216	199
Dividends payable	212	0
Total current liabilities	4,216	4,262
Fiduciary liabilities	5,118	4,847
Less – cash and investments held in a fiduciary capacity	(5,118)	(4,847)
Net fiduciary assets	0	0
Long-term debt	5,813	5,225
Pension, post-retirement and post-employment benefits	1,768	1,888
Liabilities for errors and omissions	303	301
Other liabilities	1,262	1,311
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, 2018 and December 31, 2017	561	561
Additional paid-in capital	732	784
Retained earnings	14,131	13,140
Accumulated other comprehensive loss	(4,265)	(4,043)
Non-controlling interests	81	83
Stockholders' equity before treasury stock	11,240	10,525
Less – treasury shares, at cost, 55,507,129 shares at June 30, 2018 and 51,930,135 shares at December 31, 2017	(3,443)	(3,083)
Total equity	7,797	7,442
Total liabilities and stockholders' equity	$ 21,159	$ 20,429

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Fixed assets, accumulated depreciation and amortization	$ 1,857	$ 1,826
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	55,507,129	51,930,135

Consolidated Statements of Cash

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Operating cash flows:
Net income before non-controlling interests	$ 1,232	$ 1,085
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization of fixed assets and capitalized software	159	156
Amortization of intangible assets	88	80
Adjustments and payments related to contingent consideration liability	2	(13)
Provision for deferred income taxes	34	42
(Gain) loss on investments	(28)	(5)
(Gain) loss on disposition of assets	(1)	9
Share-based compensation expense	99	75
Changes in assets and liabilities:
Net receivables	(388)	(318)
Other current assets	4	(18)
Other assets	(10)	(34)
Accounts payable and accrued liabilities	30	52
Accrued compensation and employee benefits	(614)	(579)
Accrued income taxes	18	45
Contributions to pension and other benefit plans in excess of current year expense/credit	(178)	(214)
Other liabilities	(10)	9
Effect of exchange rate changes	(24)	(29)
Net cash provided by operations	413	343
Financing cash flows:
Purchase of treasury shares	(500)	(400)
Net increase in commercial paper	175	100
Proceeds from issuance of debt	592	987
Repayments of debt	(6)	(256)
Shares withheld for taxes on vested units – treasury shares	(62)	(48)
Issuance of common stock from treasury shares	48	94
Payments of deferred and contingent consideration for acquisitions	(85)	(97)
Distributions of non-controlling interests	(11)	(13)
Dividends paid	(383)	(351)
Net cash (used for) provided by financing activities	(232)	16
Investing cash flows:
Capital expenditures	(135)	(144)
Net (purchases) sales of long-term investments	(3)	12
Proceeds from sales of fixed assets	1	4
Dispositions	4	0
Acquisitions	(144)	(412)
Other, net	(2)	2
Net cash used for investing activities	(279)	(538)
Effect of exchange rate changes on cash and cash equivalents	(71)	119
Decrease in cash and cash equivalents	(169)	(60)
Cash and cash equivalents at beginning of period	1,205	1,026
Cash and cash equivalents at end of period	$ 1,036	$ 966

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, 2016		$ 561	$ 842	$ 12,388	$ (5,093)	$ (2,506)	$ 80
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(10)
Issuance of shares under stock compensation plans and employee stock purchase plans			(69)			201
Cumulative effect of adoption of new revenue recognition standard and other new accounting standards				0	0
Cumulative effect of adoption of new revenue recognition standard and other new accounting standards | Accounting Standards Update 2014-09				0
Net income	$ 1,085			1,070			15
Dividend equivalents declared – (per share amounts: $1.165 in 2018 and $1.06 in 2017)				(2)
Dividends declared – (per share amounts: $1.165 in 2018 and $1.06 in 2017)				(541)
Other comprehensive income, net of tax	552				552
Purchase of treasury shares						(400)
Distributions and other changes							(14)
Balance, end of period at Jun. 30, 2017	7,074		763	12,915	(4,541)	(2,705)	81
Balance, beginning of year at Dec. 31, 2017	7,442	$ 561	784	13,140	(4,043)	(3,083)	83
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Change in accrued stock compensation costs			(26)
Issuance of shares under stock compensation plans and employee stock purchase plans			(26)			140
Cumulative effect of adoption of new revenue recognition standard and other new accounting standards				0	(14)
Cumulative effect of adoption of new revenue recognition standard and other new accounting standards | Accounting Standards Update 2014-09				364
Net income	1,232			1,221			11
Net income | Accounting Standards Update 2014-09	1,232
Dividend equivalents declared – (per share amounts: $1.165 in 2018 and $1.06 in 2017)				(3)
Dividends declared – (per share amounts: $1.165 in 2018 and $1.06 in 2017)				(591)
Other comprehensive income, net of tax	(208)				(208)
Purchase of treasury shares						(500)
Distributions and other changes							(13)
Balance, end of period at Jun. 30, 2018	7,797		$ 732	$ 14,131	$ (4,265)	$ (3,443)	$ 81
Balance, end of period (Accounting Standards Update 2014-09) at Jun. 30, 2018	$ 7,797

Consolidated Statements of Equ8

Consolidated Statements of Equity (Unaudited) (Parenthetical) - $ / shares	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of Stockholders' Equity [Abstract]
Dividends declared per share (in dollars per share)	$ 1.165	$ 1.06
Dividend equivalents declared per share (in dollars per share)	$ 1.165	$ 1.06

Nature of Operations

Nature of Operations	6 Months Ended
	Jun. 30, 2018
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 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 Group. Mercer provides consulting expertise, advice, services and solutions in the areas of health, wealth and career. As of June 30, 2018 , Mercer had assets under delegated management of approximately $240 billion worldwide. Oliver Wyman Group provides specialized management and economic and brand consulting services. Acquisitions impacting the Risk and Insurance Services and Consulting segments are discussed in Note 8 to the consolidated financial statements.

Principles of Consolidation and

Principles of Consolidation and Other Matters	6 Months Ended
	Jun. 30, 2018
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, 2017 (the " 2017 Form 10-K"). The financial information contained herein reflects all normal recurring adjustments which are, in the opinion of management, necessary for a fair presentation of the Company’s consolidated financial statements as of and for the three and six month periods ended June 30, 2018 and 2017 . 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 of approximately $189 million , primarily related to regulatory requirements outside the United States or as collateral under captive insurance arrangements. 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 debt 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 certain equity investments, that under legacy Generally Accepted Accounting Principles, were previously accounted as available for sale securities, whereby the mark-to-market change was recorded to other comprehensive income in its consolidated balance sheet. As discussed in Note 17, effective January 1, 2018, the Company adopted new accounting guidance that requires equity investments (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. The Company recorded a cumulative-effect adjustment that increased 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. Prior periods have not been restated. 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 gains of $28 million for both the three and six month periods ended June 30, 2018 and gains of $5 million for both the three and six month periods ended June 30, 2017. The three months ended June 30, 2018 includes gains of $26 million related to mark-to-market changes in securities with readily determinable market values and gains of $2 million related to investments in private equity funds. The six months ended June 30, 2018 includes gains of $19 million related to mark-to-market changes in securities with readily determinable market values and gains of $9 million related to investments in private equity funds. The prior period gains are related to the Company's investments in private equity funds. Income Taxes The Company's effective tax rate in the second quarter of 2018 was 25.6% compared with 28.6% in the second quarter of 2017 . The effective tax rates for the first six months of 2018 and 2017 were 24.7% and 25.9% . The rate in the first half of 2018 reflects ongoing impacts of the Tax Cuts and Jobs Act (the "TCJA"), primarily the reduced 21% U.S. statutory rate and certain tax planning benefits, largely offset by higher estimated costs from the new territorial system, greater disallowance of compensation and entertainment deductions and a decrease in excess tax benefits related to share-based compensation. The tax rates in 2017 reflect foreign operations taxed at rates below the 35% U.S. statutory tax rate, including the effect of repatriation. The tax rates in both periods reflect the impact of discrete tax matters, tax legislation and nontaxable adjustments to contingent acquisition consideration. As a result of TCJA, two discrete provisional charges were recorded in the fourth quarter of 2017. The transition to the new territorial tax system resulted in a transition tax payable over eight years on undistributed earnings of non-U.S. subsidiaries. This mandatory taxation of accumulated foreign earnings substantially changed the economic considerations of continued permanent investment of those accumulated earnings, a key component of the Company's global capital strategy. As a result of the transition tax, the Company anticipates repatriating the majority of the accumulated earnings that it previously intended to permanently invest. A charge of $240 million was recorded in the fourth quarter of 2017 as a provisional estimate of the transition tax and ancillary effects. The provisional estimate of transition tax includes state taxes and foreign withholding taxes related to the change in the Company's indefinite reinvestment assertion with respect to its pre-2018 foreign earnings. The Company previously considered most unremitted earnings of its non-U.S. subsidiaries, except amounts repatriated in the year earned, to be permanently reinvested and, accordingly, recorded no deferred U.S. income taxes on such earnings. The Company has initially analyzed its global capital requirements and potential tax liabilities attributable to repatriation. The Company estimates that it will repatriate $3.4 billion that was previously considered indefinitely invested. Included in the $240 million charge in 2017 is a $53 million provisional estimate for withholding and state income taxes. In addition, reducing the U.S. corporate tax rate from 35% to 21% and the change in deductibility of certain compensation awards to certain executive officers of the Company effective on January 1, 2018, resulted in a net charge of $220 million in the fourth quarter of 2017 to reduce the value of our U.S. deferred tax assets and liabilities. Adjustments during the first half of 2018 to provisional estimates of transition taxes and U.S. deferred tax assets and liabilities increased income tax expense by $3 million . These estimates may be further adjusted during 2018 when the Company has finalized its analysis of all the relevant information. In December of 2017, the SEC issued Staff Accounting Bulletin 118 ("SAB 118"), establishing a one-yea r measurement period to complete the accounting for the income tax effects of the TCJA. SAB 118 anticipates three alternative states of completion at the end of the reporting period of accounting for these effects: (1) the tax accounting work has been completed with respect to an item; (2) a provisional amount has been recognized because a reasonable estimate was possible, or (3) a reasonable estimate cannot be provided. The Company believes its analysis of the TCJA to date provides an appropriate basis to record a provisional estimate. Our provisional estimates include the effects of the deemed repatriation tax and the Company's position with respect to permanently reinvested earnings, the impact of the Global Intangible Low Taxed Income ("GILTI") provision and the remeasurement of U.S. deferred tax based on estimated enactment-date deferred tax balances, which may be adjusted in 2018 when the 2017 tax return is filed. TCJA’s transition tax requires detailed calculations of current and accumulated taxable earnings at the level of each foreign subsidiary, computed in functional currency at the greater of two alternative measurement dates and converted into U.S. dollars. In preparing its 2017 U.S. federal return the Company is performing these calculations for approximately seven hundred foreign subsidiaries. In the third quarter management expects to update its estimate of the transition tax, its global permanent investment strategy, and the impact on U.S. deferred tax assets from the change in tax rate. However, given the significant complexity of the TCJA and still-anticipated guidance from the U.S. Treasury about its implementation, these estimates may be further adjusted during the fourth quarter. 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 increased from $71 million at December 31, 2017 to $72 million at June 30, 2018 due to current accruals partially offset by settlements of audits and expirations of statutes of limitation. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $8 million within the next twelve months due to settlements of audits and expirations of statutes of limitation.

Revenue

Revenue	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Revenue	Revenue 2018 - Under the New Revenue Recognition Standard In May 2014, the Financial Accounting Standards Board ("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. 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. The Company adopted the new guidance effective January 1, 2018, using the modified retrospective method, which applies the new guidance beginning in 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 Company elected to apply the modified retrospective method to all contracts. The comparative financial information included herein has not been restated and continues to be reported under the legacy accounting standards that were in effect for those periods. In the first quarter of 2018, the Company recorded an increase to the opening balance of retained earnings of $ 364 million to reflect the cumulative effect of adopting this revenue standard. Other revenue included in the consolidated statements of income that is not from contracts with customers is less than one-quarter of one percent of total revenue, and therefore is not presented as a separate line item. As discussed in more detail below, the adoption of this new revenue standard will shift income among quarters from historical patterns, but is not expected to have a significant year-over-year impact on annual revenue. 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 is recognized on the effective date of the treaty. Payment terms depend on the type of reinsurance. For XOL treaties, brokerage 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 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 70% 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 various components of the Company's revenue: Three Months Ended Six Months Ended 2018 2018 Marsh: EMEA $ 526 $ 1,169 Asia Pacific 183 347 Latin America 99 183 Total International 808 1,699 U.S./Canada 941 1,744 Total Marsh 1,749 3,443 Guy Carpenter 332 969 Subtotal 2,081 4,412 Fiduciary interest income 15 28 Total Risk and Insurance Services $ 2,096 $ 4,440 Mercer: Defined Benefit Consulting & Administration $ 320 $ 659 Investment Management & Related Services 232 458 Total Wealth 552 1,117 Health 429 871 Career 177 341 Total Mercer 1,158 2,329 Oliver Wyman 492 989 Total Consulting $ 1,650 $ 3,318 The following schedule provides contract assets and contract liabilities information from contracts with customers. (In millions) January 1, 2018 June 30, 2018 Contract Assets $ 128 $ 178 Contract Liabilities $ 583 $ 647 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, 2018 to June 30, 2018 is primarily due to $215 million of additions during the period partly offset by $166 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. Revenue recognized in the first six months of 2018 that was included in the contract liability balance at the beginning of the year was $334 million . The amount of revenue recognized in the first six months of 2018 from performance obligations satisfied in previous periods, mainly due to variable consideration from contracts with insurers, quota share and excess of loss business and consulting contracts previously considered constrained was $36 million . 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 $48 million for Marsh, $450 million for Mercer and $2 million for Oliver Wyman. The Company expects revenue in 2019, 2020, 2021, 2022 and 2023 and beyond of $239 million , $129 million , $74 million , $41 million and $17 million , respectively, related to these performance obligations. Costs to Obtain and Fulfill a Contract Under the new standard, certain costs to obtain or fulfill a contract that were previously expensed as incurred have been capitalized. The Company capitalized the incremental costs to obtain contracts primarily related to commissions or sales bonus payments. These deferred costs are amortized over the expected life of the underlying customer relationships. In Risk and Insurance Services, the Company capitalizes certain pre-placement costs that are considered fulfillment costs that meet the following criteria: these costs 1) relate directly to a contract, 2) enhance resources used to satisfy the Company’s performance obligation and 3) are expected to be recovered through revenue generated by the contract. These costs are amortized at a point in time when the associated revenue is recognized. In Consulting, the Company incurs implementation costs necessary to facilitate the delivery of the contracted services. These costs are capitalized and amortized over the initial contract term plus expected renewal periods. At June 30, 2018 , the Company’s capitalized assets related to deferred implementation costs, costs to obtain and costs to fulfill were $39 million , $196 million and $154 million , respectively. Costs to obtain and deferred implementation costs are primarily included in other assets and costs to fulfill are primarily included in other current assets in the Company's consolidated balance sheet. The Company recorded amortization expense of $261 million and $557 million for the three and six month periods ended June 30, 2018 , respectively, related to these capitalized costs. The Company has elected to use the practical expedient and recognizes the incremental costs of obtaining contracts as an expense when incurred if the amortization period of the assets is one year or less. 2017 - Revenue Recognized Under Guidance in Effect Prior to 2018 Risk and Insurance Services revenue includes insurance commissions, fees for services rendered and interest income on certain fiduciary funds. Insurance commissions and fees for risk transfer services generally were recorded as of the effective date of the applicable policies or, in certain cases (primarily in the Company's reinsurance broking operations), as of the effective date or billing date, whichever is later. A reserve for policy cancellation was provided based on historic and current data on cancellations. Consideration for fee arrangements covering multiple insurance placements, the provision of risk management and/or other services was allocated to all deliverables on the basis of the relative selling prices. Fees for non-risk transfer services provided to clients are recognized over the period in which the services are provided, using a proportional performance model. Fees resulting from achievement of certain performance thresholds are recorded when such levels are attained and such fees are not subject to forfeiture. In the Consulting segment, the adoption of the new revenue standard did not have a significant impact on the timing of revenue recognition in the quarter. See Note 17 for further discussion on the impact the new revenue recognition standard has on the Company's consolidated statements of income when comparing the 2018 financial information versus 2017.

Fiduciary Assets and Liabilitie

Fiduciary Assets and Liabilities	6 Months Ended
	Jun. 30, 2018
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 of $15 million and $28 million for the three and six months ended June 30, 2018 , respectively, and $9 million and $17 million for the three and six month periods ended June 30, 2017 , respectively. The Consulting segment recorded fiduciary interest income of $1 million and $2 million for the three and six months ended June 30, 2018 , respectively, and less than $1 million and $1 million for the three and six months ended June 30, 2017 , respectively. Since fiduciary assets are not available for corporate use, they are shown in the consolidated balance sheets as an offset to fiduciary liabilities. Net uncollected premiums and claims and the related payables amounted to $8.3 billion at June 30, 2018 and $6.8 billion at December 31, 2017 . The Company is not a principal to the contracts under which the right to receive premiums or the right to receive reimbursement of insured losses arises. Accordingly, net uncollected premiums and claims and the related payables are not assets and liabilities of the Company and are not included in the accompanying consolidated balance sheets. In certain instances, the Company advances premiums, refunds or claims to insurance underwriters or insureds prior to collection. These advances are made from corporate funds and are reflected in the accompanying consolidated balance sheets as receivables.

Per Share Data

Per Share Data	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Per Share Data	Per Share Data Basic net income per share attributable to the Company is calculated by dividing the after-tax income attributable to the Company by the weighted average number of outstanding shares of the Company’s common stock. Diluted net income per share attributable to the Company is calculated by dividing the after-tax income attributable to the Company by the weighted average number of outstanding shares of the Company’s common stock, which have been adjusted for the dilutive effect of potentially issuable common shares. Basic and Diluted EPS Calculation Three Months Ended Six Months Ended (In millions, except per share amounts) 2018 2017 2018 2017 Net income before non-controlling interests $ 536 $ 507 $ 1,232 $ 1,085 Less: Net income attributable to non-controlling interests 5 6 11 15 Net income attributable to the Company $ 531 $ 501 $ 1,221 $ 1,070 Basic weighted average common shares outstanding 507 514 507 514 Dilutive effect of potentially issuable common shares 5 6 6 7 Diluted weighted average common shares outstanding 512 520 513 521 Average stock price used to calculate common stock equivalents $ 81.64 $ 75.41 $ 82.24 $ 73.36 There were 10.5 million and 12.4 million stock options outstanding as of June 30, 2018 and 2017 , respectively.

Supplemental Disclosures to the

Supplemental Disclosures to the Consolidated Statements of Cash Flows	6 Months Ended
	Jun. 30, 2018
Supplemental Cash Flow Information [Abstract]
Supplemental Disclosures to the Consolidated Statements of Cash Flows	Supplemental Disclosures to the Consolidated Statements of Cash Flows The following schedule provides additional information concerning acquisitions, interest and income taxes paid for the six-month periods ended June 30, 2018 and 2017 . (In millions) 2018 2017 Assets acquired, excluding cash $ 204 $ 576 Liabilities assumed (28 ) (74 ) Contingent/deferred purchase consideration (32 ) (90 ) Net cash outflow for current year acquisitions $ 144 $ 412 (In millions) 2018 2017 Interest paid $ 107 $ 92 Income taxes paid, net of refunds $ 349 $ 297 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 $85 million for the six months ended June 30, 2018 . This consisted of deferred purchase consideration related to prior years' acquisitions of $53 million and contingent consideration of $32 million . For the six months ended June 30, 2017 , the Company paid deferred and contingent consideration of $97 million , consisting of deferred purchase consideration related to prior years' acquisitions of $37 million and contingent consideration of $60 million . The following amounts are included in the operating section of the consolidated statements of cash flows. For the six months ended June 30, 2018 , the Company recorded an expense for adjustments to contingent consideration liabilities of $ 11 million and made contingent consideration payments of $9 million . For the six months ended June 30, 2017 , the Company recorded a net credit for adjustments to contingent consideration liabilities of $8 million and made contingent consideration payments of $5 million . The Company had non-cash issuances of common stock under its share-based payment plan of $128 million and $87 million for the six months ended June 30, 2018 and 2017 , respectively. The Company recorded stock-based compensation expense for equity awards related to restricted stock units, performance stock units and stock options of $99 million and $75 million for the six -month periods ended June 30, 2018 and 2017 , respectively.

Other Comprehensive Income (Los

Other Comprehensive Income (Loss)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) The changes, net of tax, in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the three and six -month period ended June 30, 2018 and 2017 , 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 April 1, 2018 $ — $ (2,963 ) $ (942 ) $ (3,905 ) Other comprehensive income (loss) before reclassifications — 129 (516 ) (387 ) Amounts reclassified from accumulated other comprehensive income — 27 — 27 Net current period other comprehensive income (loss) — 156 (516 ) (360 ) Balance as of June 30, 2018 $ — $ (2,807 ) $ (1,458 ) $ (4,265 ) (In millions) Unrealized Investment Gains Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of April 1, 2017 $ 16 $ (3,208 ) $ (1,645 ) $ (4,837 ) Other comprehensive income (loss) before reclassifications 14 (40 ) 289 263 Amounts reclassified from accumulated other comprehensive income — 33 — 33 Net current period other comprehensive income (loss) 14 (7 ) 289 296 Balance as of June 30, 2017 $ 30 $ (3,215 ) $ (1,356 ) $ (4,541 ) (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 — 29 (293 ) (264 ) Amounts reclassified from accumulated other comprehensive income — 56 — 56 Net current period other comprehensive income (loss) — 85 (293 ) (208 ) Balance as of June 30, 2018 $ — $ (2,807 ) $ (1,458 ) $ (4,265 ) (In millions) Unrealized Investment Gains Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2016 $ 19 $ (3,232 ) $ (1,880 ) $ (5,093 ) Other comprehensive income (loss) before reclassifications 11 (46 ) 524 489 Amounts reclassified from accumulated other comprehensive income — 63 — 63 Net current period other comprehensive income (loss) 11 17 524 552 Balance as of June 30, 2017 $ 30 $ (3,215 ) $ (1,356 ) $ (4,541 ) The components of other comprehensive income (loss) for the three and six -month period ended June 30, 2018 and 2017 are as follows: Three Months Ended June 30, 2018 2017 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (529 ) $ (13 ) $ (516 ) $ 290 $ 1 $ 289 Unrealized investment gains — — — 24 10 14 Pension/post-retirement plans: Amortization of losses included in net periodic pension cost: Prior service credits (a) (1 ) — (1 ) — — — Net actuarial losses (a) 37 9 28 42 9 33 Subtotal 36 9 27 42 9 33 Effect of remeasurement — — — — 1 (1 ) Foreign currency translation adjustments 156 27 129 (47 ) (8 ) (39 ) Pension/post-retirement plans gains (losses) 192 36 156 (5 ) 2 (7 ) Other comprehensive (loss) income $ (337 ) $ 23 $ (360 ) $ 309 $ 13 $ 296 (a) Components of net periodic pension cost are included in compensation and benefits in the consolidated statements of income. Income tax credits on prior service costs and net actuarial losses are included in income tax expense. Six Months Ended June 30, 2018 2017 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (301 ) $ (8 ) $ (293 ) $ 525 $ 1 $ 524 Unrealized investment gains — — — 19 8 11 Pension/post-retirement plans: Amortization of losses included in net periodic pension cost: Prior service credits (a) (2 ) — (2 ) — — — Net actuarial losses (a) 74 16 58 82 19 63 Subtotal 72 16 56 82 19 63 Effect of remeasurement — — — 9 3 6 Effect of curtailment — — — (1 ) — (1 ) Effect of settlement — — — 1 — 1 Foreign currency translation adjustments 36 7 29 (62 ) (11 ) (51 ) Other — — — (1 ) — (1 ) Pension/post-retirement plans gains 108 23 85 28 11 17 Other comprehensive (loss) income $ (193 ) $ 15 $ (208 ) $ 572 $ 20 $ 552 (a) Components of net periodic pension cost are included in other net benefit credits in the consolidated statements of income. Tax on prior service costs and net actuarial losses is included in income tax expense.

Acquisitions

Acquisitions	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Acquisitions	Acquisitions The Company's strategy includes growing its businesses and building shareholder value through strategic acquisitions. 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 lists, developed technology, trademarks and non-compete agreements. The valuation of purchased intangible assets involves significant estimates and assumptions. Refinement and completion of final valuation of net assets acquired could affect the carrying value of tangible assets, goodwill and identifiable intangible assets. The Risk and Insurance Services segment completed seven acquisitions during the first six months of 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. The Consulting segment completed five acquisitions during the first six months of 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. Total purchase consideration for acquisitions made during the six months ended June 30, 2018 was $192 million , which consisted of cash paid of $160 million and deferred purchase and estimated contingent consideration of $32 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 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. The Company also paid $53 million of deferred purchase consideration and $41 million of contingent consideration related to acquisitions made in prior years. The following table presents the preliminary allocation of the acquisition cost to the assets acquired and liabilities assumed during 2018 based on their fair values: For the Six Months Ended June 30, 2018 (In millions) Cash $ 160 Estimated fair value of deferred/contingent consideration 32 Total Consideration $ 192 Allocation of purchase price: Cash and cash equivalents $ 16 Accounts receivable, net 12 Property, plant, and equipment 3 Other intangible assets 73 Goodwill 116 Total assets acquired 220 Current liabilities 10 Other liabilities 18 Total liabilities assumed 28 Net assets acquired $ 192 Other intangible assets acquired are based on initial estimates and subject to change based on final valuations during the measurement period post acquisition date. The following chart provides information about other intangible assets acquired during 2018 : Amount Weighted Average Amortization Period Client relationships $ 72 9 years Other 1 4 years $ 73 Prior-Year Acquisitions The Risk and Insurance Services segment completed seven acquisitions during 2017 . • January – MMA acquired J. Smith Lanier & Co. ("JSL"), a privately held insurance brokerage firm providing insurance, risk management, and employee benefits solutions to businesses and individuals throughout the U.S. • February – MMA acquired iaConsulting, a Texas-based employee benefits consulting firm. • March – MMA acquired Blakestad, Inc., a Minnesota-based private client and commercial lines insurance agency, and RJF Financial Services, a Minnesota-based retirement advisory firm. • May – MMA acquired Insurance Partners of Texas, a Texas-based employee benefits consulting firm. • August – Marsh acquired International Catastrophe Insurance Managers, LLC, a Colorado-based managing general agent providing property catastrophe insurance to business and homeowners, and MMA acquired Hendrick & Hendrick, Inc., a Texas-based insurance agency. The Consulting segment completed three acquisitions during 2017 . • August – Mercer acquired Jaeson Associates, a Portugal-based talent management consulting organization. • December – Mercer acquired Promerit AG, a Germany-based consultancy specializing in HR digitalization and business and HR transformation and BFC Asset Management Co., Ltd., a Japan-based independently owned asset manager, focused on alternative investment strategies. Total purchase consideration for acquisitions made during the first six months of 2017 was $510 million , which consisted of cash paid of $420 million and deferred purchase and estimated contingent consideration of $90 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 earnings of the acquired entities. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment when purchase accounting is finalized. In the first six months of 2017, the Company also paid $37 million of deferred purchase consideration and $65 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 2018 and 2017. 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, 2017 and reflects acquisitions made in 2017 as if they occurred on January 1, 2016. The unaudited pro-forma information adjusts for the effects of amortization of acquired intangibles. The unaudited pro-forma financial data is presented for illustrative purposes only and is not necessarily indicative of the operating results that would have been achieved if such acquisitions had occurred on the dates indicated, nor is it necessarily indicative of future consolidated results. Three Months Ended Six Months Ended (In millions, except per share figures) 2018 2017 2018 2017 Revenue $ 3,748 $ 3,539 $ 7,770 $ 7,098 Net income attributable to the Company $ 532 $ 503 $ 1,225 $ 1,072 Basic net income per share attributable to the Company $ 1.05 $ 0.98 $ 2.41 $ 2.08 Diluted net income per share attributable to the Company $ 1.04 $ 0.97 $ 2.39 $ 2.06 The consolidated statements of income include the results of operations of acquired companies since their respective acquisition dates. The consolidated statements of income for the three and six month periods ended June 30, 2018 include approximately $11 million and $14 million of revenue, respectively, and an operating loss of $1 million and $2 million , respectively, for acquisitions made in 2018. The consolidated statements of income for the three and six month periods ended June 30, 2017 included $34 million and $63 million of revenue, respectively, and operating income of $5 million and $15 million , respectively, related to acquisitions made in 2017. Subsequent Events On June 25th, the Company announced an agreement to acquire Wortham Insurance, a Houston based independent insurance broker with more than $130 million of revenue and 530 colleagues. The transaction is expected to close in the third quarter of 2018. In July, 2018, the Company entered into a agreement to sell Marsh ClearSight, a cloud based technology platform. The disposal of Marsh ClearSight is not expected to have a significant impact on the Company’s ongoing revenue or results of operations.

Goodwill and Other Intangibles

Goodwill and Other Intangibles	6 Months Ended
	Jun. 30, 2018
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, the Company assesses qualitative factors to determine whether it is necessary to perform the two-step goodwill impairment test. As part of its assessment, the Company considers numerous factors, including that the fair value of each reporting unit exceeds its carrying value by a substantial margin based on its most recent estimates, whether significant acquisitions or dispositions occurred which might alter the fair value of its reporting units, macroeconomic conditions and their potential impact on reporting unit fair values, actual performance compared with budget and prior projections used in its estimation of reporting unit fair values, industry and market conditions, and the year-over-year change in the Company’s share price. The Company completed its qualitative assessment in the third quarter of 2017 and concluded that a two-step goodwill impairment test was not required in 2017 and that goodwill was not impaired. Changes in the carrying amount of goodwill are as follows: June 30, (In millions) 2018 2017 Balance as of January 1, $ 9,089 $ 8,369 Goodwill acquired 116 370 Other adjustments (a) (28 ) 82 Balance at June 30, $ 9,177 $ 8,821 (a) Primarily reflects the impact of foreign exchange. Goodwill allocable to the Company’s reportable segments at June 30, 2018 is as follows: Risk and Insurance Services, $6.5 billion and Consulting, $2.7 billion . 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 gross cost and accumulated amortization at June 30, 2018 and December 31, 2017 are as follows: June 30, 2018 December 31, 2017 (In millions) Gross Cost Accumulated Amortization Net Carrying Amount Gross Cost Accumulated Amortization Net Carrying Amount Client Relationships $ 1,711 $ 580 $ 1,131 $ 1,672 $ 518 $ 1,154 Other (a) 237 134 103 234 114 120 Amortized intangibles $ 1,948 $ 714 $ 1,234 $ 1,906 $ 632 $ 1,274 (a) Primarily non-compete agreements, trade names and developed technology. Aggregate amortization expense for the six months ended June 30, 2018 and 2017 was $88 million and $80 million , respectively. The estimated future aggregate amortization expense is as follows: For the Years Ending December 31, (In millions) Estimated Expense 2018 (excludes amortization through June 30, 2018) $ 94 2019 173 2020 154 2021 143 2022 132 Subsequent years 538 $ 1,234

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2018
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). The Company does not have any assets or liabilities that are measured using Level 2 inputs. 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. Liabilities measured using Level 3 inputs include liabilities for contingent purchase consideration. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued using a valuation technique that results in price per share at $1.00 . Contingent Purchase Consideration Liability – Level 3 Purchase consideration for some acquisitions made by the Company includes 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 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 entities. The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 . Identical Assets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Total (In millions) 06/30/18 12/31/17 06/30/18 12/31/17 06/30/18 12/31/17 06/30/18 12/31/17 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 99 $ 81 $ — $ — $ — $ — $ 99 $ 81 Mutual funds (a) 144 158 — — — — 144 158 Money market funds (b) 33 143 — — — — 33 143 Total assets measured at fair value $ 276 $ 382 $ — $ — $ — $ — $ 276 $ 382 Fiduciary Assets: Money market funds $ 129 $ 111 $ — $ — $ — $ — $ 129 $ 111 Total fiduciary assets measured at fair value $ 129 $ 111 $ — $ — $ — $ — $ 129 $ 111 Liabilities: Contingent purchase consideration liability (c) $ — $ — $ — $ — $ 185 $ 189 $ 185 $ 189 Total liabilities measured at fair value $ — $ — $ — $ — $ 185 $ 189 $ 185 $ 189 (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. During the six -month period ended June 30, 2018 , there were no assets or liabilities that were transferred between any of the levels. The table below sets forth a summary of the changes in fair value of the Company’s Level 3 liabilities for the three and six month periods ending June 30, 2018 and 2017 that represent contingent consideration related to acquisitions: Three Months Ended Six Months Ended (In millions) 2018 2017 2018 2017 Balance at beginning of period, $ 161 $ 247 $ 189 $ 241 Additions 20 — 26 34 Payments (1 ) (53 ) (41 ) (65 ) Revaluation Impact 6 8 11 (8 ) Other (a) (1 ) 1 — 1 Balance at June 30, $ 185 $ 203 $ 185 $ 203 (a) Primarily reflects the impact of foreign exchange. The fair value of the contingent purchase consideration liability is based on projections of revenue and EBITDA for the acquired entities in relation to the established targets and is reassessed on a quarterly basis. 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 $11 million in the six -month period ended June 30, 2018 . A 5% increase in the above mentioned projections would increase the liability by approximately $22 million . A 5% decrease in the above mentioned projections would decrease the liability by approximately $23 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 $391 million and $405 million at June 30, 2018 and December 31, 2017 , 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, a South African company listed on the Johannesburg Stock Exchange, which it purchased in 2014 for 7.50 South African Rand per share. As of June 30, 2018 , the carrying value of the Company’s investment in Alexander Forbes was approximately $246 million . As of June 30, 2018 , the market value of the approximately 443 million shares of Alexander Forbes owned by the Company, based on the June 30, 2018 closing share price of 5.77 South African Rand per share, was approximately $188 million . The Company considered several factors in assessing its investment in Alexander Forbes, including its financial position, the near- and long-term prospects of Alexander Forbes and the broader South African economy and capital markets, the length of time and extent to which the market value was below cost and the Company’s intent and ability to retain the investment for a sufficient period of time to allow for anticipated recovery in market value. During the first six months of 2018, the Alexander Forbes average opening and closing stock price was approximately 6.66 Rand (approximately 89% of the original purchase price) and ranged from a low of 5.00 Rand (in mid June) to a high of 7.34 Rand (in late March) (approximately 67% to 98% of the purchase price) and traded within 10% of its purchase price as recently as early-June. The trading price declined further during July, 2018. Based on its assessment of the factors discussed above, in particular the relatively short period during which the shares traded significantly below their purchase price, and the Company’s intention to continue to hold the shares for a period of time sufficient to allow for recovery, the Company determined the investment was not impaired. However, if the share price does not recover in future periods, an impairment charge for an "other than temporary" decline in value of its investment could be incurred. The Company has other investments in private insurance and consulting companies with a carrying value of $63 million at both June 30, 2018 and December 31, 2017. The Company’s investment in Alexander Forbes and its other equity investments in private 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 on a one quarter lag basis. Private Equity Investments The Company's investments in private equity funds were $82 million and $76 million at June 30, 2018 and December 31, 2017 , respectively. The carrying values of these private equity investments approximate fair value. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. The Company records in earnings its proportionate share of the change in fair value of the funds on the investment income (loss) line in the consolidated statements of income. These investments are included in other assets in the consolidated balance sheets. Other Investments At June 30, 2018 the Company held certain equity investments with readily determinable market values of $113 million . During the first six months of 2018 , the Company recorded an investment gain of $19 million , which reflects the increase in the market value of these investments as compared to December 31, 2017. The Company also holds investments without readily determinable market values of $64 million at June 30, 2018.

Retirement Benefits

Retirement Benefits	6 Months Ended
	Jun. 30, 2018
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 and at June 30, 2018 the actual allocation for the Company's U.S. Plan was 63% equities and equity alternatives and 37% fixed income. The target allocation for the U.K. Plans at June 30, 2018 was 34% equities and equity alternatives and 66% fixed income. At June 30, 2018 , the actual allocation for the U.K. Plans was 35% equities and equity alternatives and 65% fixed income. The Company's U.K. Plans comprised approximately 81% of non-U.S. plan assets at December 31, 2017 . The assets of the Company's defined benefit plans are diversified and are managed in accordance with applicable laws and with the goal of maximizing the plans' real return within acceptable risk parameters. The Company generally uses threshold-based portfolio re-balancing to ensure the actual portfolio remains consistent with target asset allocation ranges. The components of the net periodic benefit cost for defined benefit and other post-retirement plans are as follows: Combined U.S. and significant non-U.S. plans Pension Benefits Post-retirement Benefits For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 7 $ 19 $ — $ — Interest cost 117 124 1 1 Expected return on plan assets (218 ) (230 ) — — Amortization of prior service cost (1 ) (1 ) (1 ) — Recognized actuarial loss 37 43 — — Net periodic benefit (credit) cost $ (58 ) $ (45 ) $ — $ 1 Combined U.S. and significant non-U.S. plans Pension Benefits Post-retirement Benefits For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 17 $ 37 $ — $ — Interest cost 235 246 2 2 Expected return on plan assets (439 ) (454 ) — — Amortization of prior service (credit) cost (1 ) (1 ) (2 ) 1 Recognized actuarial loss 74 83 — — Net periodic benefit (credit) cost $ (114 ) $ (89 ) $ — $ 3 Curtailment gain — (1 ) — — Settlement loss — 1 — — Total (credit) cost $ (114 ) $ (89 ) $ — $ 3 As discussed in Note 17, effective January 1, 2018, the Company adopted the new guidance that changes the presentation of net periodic pension cost and net periodic postretirement cost (''net periodic benefit costs"). The new guidance requires employers to report the service cost component of net periodic benefit costs in the same line item as other compensation costs in the income statement. The other components of net periodic benefit costs are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The new guidance requires retrospective application for the presentation of the service cost component and the other components of net periodic benefit costs. Accordingly, the Company has reclassified prior period information in the following chart to conform with the current year's presentation: Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. plans Pension Post-retirement For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Compensation and benefits expense (Operating income) $ 7 $ 19 $ — $ — Other net benefit credits (65 ) (64 ) — 1 Total (credit) cost $ (58 ) $ (45 ) $ — $ 1 Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. plans Pension Post-retirement For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Compensation and benefits expense (Operating income) $ 17 $ 37 $ — $ — Other net benefit credits (131 ) (126 ) — 3 Total (credit) cost $ (114 ) $ (89 ) $ — $ 3 U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ — $ — $ — $ — Interest cost 59 66 1 1 Expected return on plan assets (90 ) (90 ) — — Amortization of prior service (credit) cost — — (1 ) 1 Recognized actuarial loss (gain) 14 10 — (1 ) Net periodic benefit (credit) cost $ (17 ) $ (14 ) $ — $ 1 U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ — $ — $ — $ — Interest cost 118 132 1 1 Expected return on plan assets (179 ) (179 ) — — Amortization of prior service (credit) cost — — (1 ) 2 Recognized actuarial loss (gain) 27 19 — (1 ) Net periodic benefit (credit) cost $ (34 ) $ (28 ) $ — $ 2 Significant non-U.S. plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 7 $ 19 $ — $ — Interest cost 58 58 — — Expected return on plan assets (128 ) (140 ) — — Amortization of prior service cost (1 ) (1 ) — (1 ) Recognized actuarial loss 23 33 — 1 Net periodic benefit (credit) cost $ (41 ) $ (31 ) $ — $ — Significant non-U.S. plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 17 $ 37 $ — $ — Interest cost 117 114 1 1 Expected return on plan assets (260 ) (275 ) — — Amortization of prior service credit (1 ) (1 ) (1 ) (1 ) Recognized actuarial loss 47 64 — 1 Net periodic benefit (credit) cost $ (80 ) $ (61 ) $ — $ 1 Curtailment gain — (1 ) — — Settlement loss — 1 — — Total (credit) cost $ (80 ) $ (61 ) $ — $ 1 In March 2017, the Company modified its defined benefit pension plans in Canada to discontinue further benefit accruals for participants after December 31, 2017 and replaced them with a defined contribution arrangement. The Company also amended its post-retirement benefits plan in Canada so that individuals who retire after April 1, 2019 will not be eligible to participate, except in certain situations. The Company re-measured the assets and liabilities of the plans, based on assumptions and market conditions on the amendment date. The weighted average actuarial assumptions utilized to calculate the net periodic benefit costs for the U.S. and significant non-U.S. defined benefit plans are as follows: Combined U.S. and significant non-U.S. plans Pension Post-retirement June 30, 2018 2017 2018 2017 Weighted average assumptions: Expected return on plan assets 5.83 % 6.64 % — — Discount Rate 3.07 % 3.40 % 3.21 % 3.64 % Rate of compensation increase 1.73 % 1.77 % — — The Company made approximately $55 million of contributions to its U.S. and non-U.S. defined benefit plans in the first six months of 2018 . The Company expects to contribute approximately $54 million to its U.S. pension and non-U.S. pension plans during the remainder of 2018 . 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 $67 million and $65 million for the six months ended June 30, 2018 and 2017 , respectively. The cost of the U.K. DC Plans was $42 million and $38 million for the six months ended June 30, 2018 and 2017 , respectively.

Debt

Debt	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Debt	Debt The Company’s outstanding debt is as follows: (In millions) June 30, December 31, Short-term: Commercial paper $ 175 $ — Current portion of long-term debt 264 262 439 262 Long-term: Senior notes – 2.55% due 2018 250 250 Senior notes – 2.35% due 2019 299 299 Senior notes – 2.35% due 2020 499 498 Senior notes – 4.80% due 2021 498 498 Senior notes – 2.75% due 2022 497 496 Senior notes – 3.30% due 2023 348 348 Senior notes – 4.05% due 2023 248 248 Senior notes – 3.50% due 2024 597 596 Senior notes – 3.50% due 2025 496 496 Senior notes – 3.75% due 2026 596 596 Senior notes – 5.875% due 2033 297 297 Senior notes – 4.35% due 2047 492 492 Senior notes – 4.20% due 2048 592 — Mortgage – 5.70% due 2035 364 370 Other 4 3 6,077 5,487 Less current portion 264 262 $ 5,813 $ 5,225 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 $175 million of commercial paper outstanding at June 30, 2018 at an effective interest rate of 2.25% . 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 January 2017, the Company issued $500 million of 2.75% senior notes due 2022 and $500 million of 4.35% senior notes due 2047. The Company used the net proceeds for general corporate purposes, including the repayment of a $250 million debt maturity in April 2017. The Company and certain of its foreign subsidiaries maintain a $1.5 billion multi-currency five -year unsecured revolving credit facility. 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 November 2020 and requires the Company to maintain certain coverage and leverage ratios which are tested quarterly. There were no borrowings outstanding under this facility at June 30, 2018 . Fair Value of Short-term and Long-term Debt The estimated fair value of the Company’s short-term and long-term debt is provided below. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts shown below are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or need to dispose of the financial instrument. June 30, 2018 December 31, 2017 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Short-term debt $ 439 $ 440 $ 262 $ 264 Long-term debt $ 5,813 $ 5,826 $ 5,225 $ 5,444 The fair value of the Company’s short-term debt consists primarily of commercial paper 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	6 Months Ended
	Jun. 30, 2018
Restructuring and Related Activities [Abstract]
Restructuring Costs	Restructuring Costs 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. During the quarter ended June 30, 2018, the Company incurred restructuring severance and consulting costs of $55 million related to this initiative. In addition to the changes discussed above, the Company incurred $9 million of restructuring costs related to severance and future rent under non-cancelable leases. These costs were incurred in Risk and Insurance Services ( $3 million ), Consulting ( $1 million ) and Corporate ( $5 million ). Details of the restructuring activity from January 1, 2017 through June 30, 2018 , which includes liabilities from actions prior to 2018 , are as follows: (In millions) Liability at 1/1/17 Amounts Accrued Cash Paid Other Liability at 12/31/17 Amounts Accrued Cash Paid Other Liability at 6/30/18 Severance $ 32 $ 31 $ (49 ) $ 1 $ 15 $ 51 $ (22 ) $ (1 ) $ 43 Future rent under non-cancelable leases and other costs 61 9 (22 ) 2 50 13 (19 ) — 44 Total $ 93 $ 40 $ (71 ) $ 3 $ 65 $ 64 $ (41 ) $ (1 ) $ 87 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.

Common Stock

Common Stock	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Common Stock	Common Stock During the first six months of 2018 , the Company repurchased approximately 6.1 million shares of its common stock for consideration of $500 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 June 30, 2018 , the Company remained authorized to repurchase up to approximately $1 billion in shares of its common stock. There is no time limit on the authorization. During the first six months of 2017 , the Company repurchased approximately 5.4 million shares of its common stock for consideration of $400 million . The Company issued approximately 2.5 million and 3.7 million shares related to stock compensation and employee stock purchase plans during the first six months of 2018 and 2017 , respectively.

Claims, Lawsuits And Other Cont

Claims, Lawsuits And Other Contingencies	6 Months Ended
	Jun. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
Claims, Lawsuits, and Other Contingencies	Claims, Lawsuits and Other Contingencies 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 office of Marsh Limited, our Marsh and Guy Carpenter operating subsidiary in the United Kingdom. The FCA indicated that it had reasonable grounds for suspecting that Marsh Limited 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 Marsh, 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 at the same time that it has 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 in connection with this matter. In July 2017, the Directorate-General for Competition of the European Commission together with the Irish Competition and Consumer Protection Commission conducted on-site inspections at the offices of Marsh and other industry participants in Dublin in connection with an investigation regarding the "possible participation in anticompetitive agreements and/or concerted practices contrary to [E.U. competition law] in the market for commercial motor insurance in the Republic of Ireland." 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. In November 2017, the FCA announced the terms of reference for a market study concerning the wholesale insurance broker sector in the United Kingdom, which affects Marsh and Guy Carpenter. The FCA is conducting the study to assess "how effectively competition is working in the wholesale insurance broker sector" and "how brokers influence competition in the underwriting sector." The FCA is expected to publish its interim report by the end of 2018, with a final report expected in 2019. Consulting Segment In June 2017, the FCA issued a final report in connection with a market study of the U.K. asset management industry, which includes asset managers and investment consultants, including Mercer. Following the report, in September 2017, the FCA announced its decision to refer the investment consultancy and fiduciary management markets to the U.K. Competition & Markets Authority (the "CMA") for a market investigation. In July 2018, the CMA published its Provisional Decision recommending industry-wide changes involving (i) implementation of mandatory tendering, (ii) enhanced fee disclosures and (iii) common standards for reporting performance. The CMA expects to conclude its investigation of the investment consultancy and fiduciary management markets not later than March 2019. In the ordinary course of business, the Company is also subject to other investigations, market studies, subpoenas, lawsuits and other regulatory actions undertaken by governmental authorities. Other Contingencies-Guarantees In connection with its acquisition of U.K.-based Sedgwick Group in 1998, the Company acquired several insurance underwriting businesses that were already in run-off, including River Thames Insurance Company Limited ("River Thames"), which the Company sold in 2001. Sedgwick guaranteed payment of claims on certain policies underwritten through the Institute of London Underwriters (the "ILU") by River Thames. The policies covered by this guarantee were reinsured up to £40 million by a related party of River Thames. Payment of claims under the reinsurance agreement is collateralized by segregated assets held in a trust. As of June 30, 2018 , 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 15 on Claims, Lawsuits and Other Contingencies may expose the Company or its subsidiaries to liability for significant monetary damages, fines, penalties or other forms of relief. Where a loss is both probable and reasonably estimable, the Company establishes liabilities in accordance with FASB guidance on Contingencies - Loss Contingencies. Except as described above, the Company is not able at this time to provide a reasonable estimate of the range of possible loss attributable to these matters or the impact they may have on the Company's consolidated results of operations, financial position or cash flows. This is primarily because these matters are still developing and involve complex issues subject to inherent uncertainty. Adverse determinations in one or more of these matters could have a material impact on the Company's consolidated results of operations, financial condition or cash flows in a future period.

Segment Information

Segment Information	6 Months Ended
	Jun. 30, 2018
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 2017 Form 10-K. Segment performance is evaluated based on segment operating income, which includes directly related expenses, and charges or credits related to integration and restructuring but not the Company’s corporate-level expenses. Revenues are attributed to geographic areas on the basis of where the services are performed. Selected information about the Company’s operating segments for the three and six -month periods ended June 30, 2018 and 2017 are as follows: Three Months Ended Six Months Ended (In millions) Revenue Operating Income (Loss) Revenue Operating Income (Loss) 2018– Risk and Insurance Services $ 2,096 (a) $ 472 $ 4,440 (c) $ 1,188 Consulting 1,650 (b) 267 3,318 (d) 514 Total Operating Segments 3,746 739 7,758 1,702 Corporate / Eliminations (12 ) (48 ) (24 ) (103 ) Total Consolidated $ 3,734 $ 691 $ 7,734 $ 1,599 2017– Risk and Insurance Services $ 1,916 (a) $ 482 $ 3,905 (c) $ 1,050 Consulting 1,592 (b) 265 3,118 (d) 490 Total Operating Segments 3,508 747 7,023 1,540 Corporate / Eliminations (13 ) (46 ) (25 ) (90 ) Total Consolidated $ 3,495 $ 701 $ 6,998 $ 1,450 (a) Includes inter-segment revenue of $4 million in 2017 , interest income on fiduciary funds of $15 million and $9 million in 2018 and 2017 , respectively, and equity method income of $7 million in both 2018 and 2017 . (b) Includes inter-segment revenue of $12 million and $9 million in 2018 and 2017 , respectively, interest income on fiduciary funds of $1 million and less than $1 million in 2018 and 2017 , respectively, and equity method income of $5 million in both 2018 and in 2017 . (c) Includes inter-segment revenue of $1 million and $4 million in 2018 and 2017 , respectively, interest income on fiduciary funds of $28 million and $17 million in 2018 and 2017 , respectively, and equity method income of $6 million and $9 million in 2018 and 2017 , respectively. (d) Includes inter-segment revenue of $23 million and $21 million in 2018 and 2017 , respectively, interest income on fiduciary funds of $2 million and $1 million in 2018 and 2017 , respectively, and equity method income of $8 million in 2018 and $9 million in 2017 , respectively. Details of operating segment revenue for the three and six -month periods ended June 30, 2018 and 2017 are as follows: Three Months Ended Six Months Ended (In millions) 2018 2017 2018 2017 Risk and Insurance Services Marsh $ 1,760 $ 1,621 $ 3,463 $ 3,223 Guy Carpenter 336 295 977 682 Total Risk and Insurance Services 2,096 1,916 4,440 3,905 Consulting Mercer 1,158 1,109 2,329 2,186 Oliver Wyman Group 492 483 989 932 Total Consulting 1,650 1,592 3,318 3,118 Total Operating Segments 3,746 3,508 7,758 7,023 Corporate / Eliminations (12 ) (13 ) (24 ) (25 ) Total $ 3,734 $ 3,495 $ 7,734 $ 6,998

New Accounting Guidance

New Accounting Guidance	6 Months Ended
	Jun. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
New Accounting Guidance	New Accounting Guidance 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: New Revenue Recognition Standard 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 Company elected to apply the modified retrospective method to all contracts. The guidance includes requirements to estimate variable or contingent consideration to be received, which will result in revenue being recognized earlier than under legacy GAAP. In addition, the guidance requires the capitalization and amortization of certain costs which were expensed as incurred under legacy GAAP. As discussed in more detail below, the adoption of this new revenue recognition standard will shift revenue among quarters from historical patterns, but is not expected to have a significant year-over-year impact on annual revenue. Upon adoption of the new revenue standard, the Company recognized significant movement in the quarterly timing of revenue recognized in the Risk and Insurance Services segment. In particular, under the new standard the recognition of revenue for reinsurance broking was accelerated from historical patterns. Estimated revenue from these treaties is recognized largely at the policy effective date at which point control over the services provided by the Company transfers to the client and the client has accepted the services. This resulted in a significant increase in revenue in the first quarter of 2018 compared to the same period in 2017. Prior to the adoption of this standard, revenue related to most reinsurance placements was recognized on the later of billing or effective date as premiums are determined by the primary insurers and attached to the reinsurance treaties. Typically, this resulted in revenue being recognized over a 12 to 18 month period. The timing of revenue recognition for certain fee based brokerage arrangements will shift among quarters. However, since the vast majority of the Company's fee arrangements involve contracts that cover a single year of services, the Company does not expect there will be a significant change in the amount of revenue recognized in an annual period. In the Risk and Insurance Services segment, certain pre-placement costs are now deferred and amortized into earnings when revenue from the placement is recognized. These costs were previously expensed as incurred. As such, the Company expects the recognition of costs to shift among quarters. In the Consulting segment, the adoption of the new revenue standard will not have a significant impact on the timing of revenue recognition in quarterly or annual periods. In Consulting, the Company incurs implementation costs necessary to facilitate the delivery of the contracted services. The Company has concluded that certain additional implementation costs previously expensed under legacy GAAP will be deferred under the new guidance. In addition, the amortization period for these implementation costs will include the initial contract term plus expected renewals. 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. The comparative prior period information was not restated and will continue to be reported under the legacy accounting standards that were in effect for those periods. The impact of adoption of the new revenue standard on the Company's consolidated income statement was as follows (in millions): Three Months Ended June 30, Six Months Ended June 30, Revenue Standard Impact Legacy GAAP As Reported Revenue Standard Impact Legacy GAAP Revenue $ 3,734 $ (24 ) $ 3,710 $ 7,734 $ (185 ) $ 7,549 Expense: Compensation and Benefits 2,135 (10 ) 2,125 4,359 (70 ) 4,289 Other Operating Expenses 908 — 908 1,776 — 1,776 Operating Expenses 3,043 (10 ) 3,033 6,135 (70 ) 6,065 Operating Income 691 (14 ) 677 1,599 (115 ) 1,484 Other Net Benefit Credits 65 — 65 131 — 131 Interest Income 3 — 3 6 — 6 Interest Expense (68 ) — (68 ) (129 ) — (129 ) Investment Income 28 — 28 28 — 28 Income Before Income Taxes 719 (14 ) 705 1,635 (115 ) 1,520 Income Tax Expense 183 (4 ) 179 403 (30 ) 373 Net Income Before Non-Controlling Interests 536 (10 ) 526 1,232 (85 ) 1,147 Less: Net Income Attributable to Non-Controlling Interests 5 — 5 11 — 11 Net Income Attributable to the Company $ 531 $ (10 ) $ 521 $ 1,221 $ (85 ) $ 1,136 The impact of adoption of the new revenue standard on the Company's consolidated balance sheet was as follows (in millions): June 30, 2018 As Reported Revenue Standard Impact Legacy GAAP ASSETS Current assets: Cash and cash equivalents $ 1,036 $ — $ 1,036 Net receivables 4,601 (254 ) 4,347 Other current assets 538 (298 ) 240 Total current assets 6,175 (552 ) 5,623 Goodwill and intangible assets 10,411 — 10,411 Fixed assets, net 698 — 698 Pension related assets 1,808 — 1,808 Deferred tax assets 532 133 665 Other assets 1,535 (230 ) 1,305 TOTAL ASSETS $ 21,159 $ (649 ) $ 20,510 LIABILITIES AND EQUITY Current liabilities: Short-term debt $ 439 $ — $ 439 Accounts payable and accrued liabilities 2,246 (177 ) 2,069 Accrued compensation and employee benefits 1,103 — 1,103 Accrued income taxes 216 — 216 Dividends payable 212 — 212 Total current liabilities 4,216 (177 ) 4,039 Fiduciary liabilities 5,118 — 5,118 Less - cash and investments held in a fiduciary capacity (5,118 ) — (5,118 ) — — — Long-term debt 5,813 — 5,813 Pension, post-retirement and post-employment benefits 1,768 — 1,768 Liabilities for errors and omissions 303 — 303 Other liabilities 1,262 (23 ) 1,239 Total equity 7,797 (449 ) 7,348 TOTAL LIABILITIES AND EQUITY $ 21,159 $ (649 ) $ 20,510 The impact of adoption of the new revenue standard on the Company's consolidated statement of cash flow was as follows (in millions): Six Months Ended June 30, 2018 As Reported Revenue Standard Impact Legacy GAAP Operating cash flows: Net income before non-controlling interests $ 1,232 $ (85 ) $ 1,147 Adjustments to reconcile net income to cash provided by operations: Depreciation and amortization of fixed assets and capitalized software 159 — 159 Amortization of intangible assets 88 — 88 Adjustments and payments related to contingent consideration liability 2 — 2 Provision for deferred income taxes 34 — 34 Gain on investments (28 ) — (28 ) Gain on disposition of assets (1 ) — (1 ) Share-based compensation expense 99 — 99 Changes in assets and liabilities: Net receivables (388 ) 186 (202 ) Other current assets 4 (20 ) (16 ) Other assets (10 ) (26 ) (36 ) Accounts payable and accrued liabilities 30 (55 ) (25 ) Accrued compensation and employee benefits (614 ) — (614 ) Accrued income taxes 18 — 18 Contributions to pension excess of expense/credit (178 ) — (178 ) Other liabilities (10 ) — (10 ) Effect of exchange rate changes (24 ) — (24 ) Net cash provided by operations $ 413 $ — $ 413 The adoption of the revenue recognition standard did not have an impact on the Company's financing or investing cash flows. Other Standards Adopted Effective January 1, 2018 using the modified retrospective approach 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 new guidance was effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company holds certain equity investments that under legacy GAAP were previously treated as available for sale securities, whereby the mark-to-market change was recorded to other comprehensive income in its consolidated balance sheet. 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. Therefore, prior periods have not been restated. 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. The impact on the Company's balance sheet as of January 1, 2018 related to the adoption of the accounting standards using the modified retrospective approach as discussed above is as follows: Adjustments Balance at December 31, 2017 Revenue Recognition Financial Instruments Intra-Entity Transfer Balance at January 1, 2018 Balance Sheet Assets Net Receivables $ 4,133 $ 68 $ — $ — $ 4,201 Other Current Assets 224 318 — — 542 Other Assets 1,430 226 — — 1,656 Deferred Tax Assets 669 (103 ) — (14 ) 552 Liabilities Accounts Payable and Accrued Liabilities 2,083 122 — — 2,205 Other Liabilities 1,311 23 — — 1,334 Equity Other Accumulated Comprehensive Income — — (14 ) — (14 ) Retained Earnings $ 13,140 $ 364 $ 14 $ (14 ) $ 13,504 Cumulative effect adjustment related to the adoption of the revenue recognition standard The cumulative effect adjustment recorded to net receivables is primarily related to contingent brokerage revenue and reinsurance revenue placements. Under the new guidance, the Company is required to record an estimate of variable or contingent consideration earlier than under the previous rules. Also under the new guidance, revenue related to most reinsurance placements is accelerated versus previous patterns. The cumulative effect adjustments also includes the capitalization of costs to fulfill and costs to obtain that are included in other current assets and other assets, respectively. These costs were previously expensed as incurred. The adjustment to accounts payable and accrued liabilities includes deferred revenue related to the timing of fee revenue recognition for fee based arrangements and certain post placement servicing costs, primarily related to reinsurance brokerage costs that were previously expensed as incurred. Adoption of amended accounting standard using the retrospective application approach Effective January 1, 2018, the Company adopted new guidance that changes the presentation of net periodic pension cost and net periodic postretirement cost (''net periodic benefit costs"). The new guidance requires employers to report the service cost component of net periodic benefit costs in the same line item as other compensation costs in the income statement. The other components of net periodic benefit costs are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The new guidance requires retrospective application for the presentation of the service cost component and the other components of net periodic benefit costs. Accordingly, we have reclassified prior period information in the consolidated results of operations, segment data and related disclosures contained in our management's discussion and analysis and notes to the consolidated financial statements to reflect the retrospective adoption of this standard. Other accounting standards adopted effective January 1, 2018 In November 2016, the FASB issued new guidance which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. As a result, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The Company adopted this guidance, which is required to be applied retrospectively to all periods presented, effective January 1, 2018. The adoption of this guidance did not impact the Company's consolidated balance sheets or consolidated statements of cash flows. In August 2016, the FASB issued new guidance which adds or clarifies guidance on the classification of certain cash receipts and payments in the statement of cash flows, including cash payments for debt prepayments or debt extinguishment costs, contingent consideration payments made after a business combination and distributions received from equity method investees. The Company adopted this guidance effective January 1, 2018. The adoption of this guidance did not impact the Company's consolidated statements of cash flows. In January 2017, the FASB issued guidance which clarifies the definition of a business in order to assist companies with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company adopted this guidance effective January 1, 2018. The adoption of this standard did not have an impact on the Company's financial position or results of operations. New Accounting Pronouncements Not Yet Adopted 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 February 2016, the FASB issued new guidance intended to improve financial reporting for leases. Under the new guidance, a lessee will be required to recognize assets and liabilities for leases with lease terms of more than 12 months. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a financing or operating lease. However, unlike current GAAP, which requires that only capital leases be recognized on the balance sheet, the new guidance requires that both types of leases be recognized on the balance sheet. The new guidance will require additional disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, and additional information about the amounts recorded in the financial statements. The accounting by organizations that own the assets ("lessor") leased by the lessee will remain largely unchanged from current GAAP. However, the guidance contains targeted improvements that are intended to align, where necessary, lessor accounting with the lessee accounting model. The new guidance on leases is effective for public companies for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early application is permitted. The Company is currently evaluating the impact the adoption of the guidance will have on its financial position and results of operations, but expects material "right of use" assets and lease liabilities to be recorded on its consolidated balance sheets.

Principles of Consolidation a26

Principles of Consolidation and Other Matters (Policies)	6 Months Ended
	Jun. 30, 2018
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 debt 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 certain equity investments, that under legacy Generally Accepted Accounting Principles, were previously accounted as available for sale securities, whereby the mark-to-market change was recorded to other comprehensive income in its consolidated balance sheet. As discussed in Note 17, effective January 1, 2018, the Company adopted new accounting guidance that requires equity investments (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. The Company recorded a cumulative-effect adjustment that increased 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. Prior periods have not been restated. The Company holds investments in certain private equity funds that are accounted for under the equity method of accounting using a consistently applied three -month lag period adjusted for any known significant changes from the lag period to the reporting date of the Company. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. Investment gains or losses for the Company's proportionate share of the change in fair value of the funds are recorded in earnings. Investments accounted for using the equity method of accounting are included in "other assets" in the consolidated balance sheets.
Income Taxes	The Company's effective tax rate in the second quarter of 2018 was 25.6% compared with 28.6% in the second quarter of 2017 . The effective tax rates for the first six months of 2018 and 2017 were 24.7% and 25.9% . The rate in the first half of 2018 reflects ongoing impacts of the Tax Cuts and Jobs Act (the "TCJA"), primarily the reduced 21% U.S. statutory rate and certain tax planning benefits, largely offset by higher estimated costs from the new territorial system, greater disallowance of compensation and entertainment deductions and a decrease in excess tax benefits related to share-based compensation. The tax rates in 2017 reflect foreign operations taxed at rates below the 35% U.S. statutory tax rate, including the effect of repatriation. The tax rates in both periods reflect the impact of discrete tax matters, tax legislation and nontaxable adjustments to contingent acquisition consideration. As a result of TCJA, two discrete provisional charges were recorded in the fourth quarter of 2017. The transition to the new territorial tax system resulted in a transition tax payable over eight years on undistributed earnings of non-U.S. subsidiaries. This mandatory taxation of accumulated foreign earnings substantially changed the economic considerations of continued permanent investment of those accumulated earnings, a key component of the Company's global capital strategy. As a result of the transition tax, the Company anticipates repatriating the majority of the accumulated earnings that it previously intended to permanently invest. A charge of $240 million was recorded in the fourth quarter of 2017 as a provisional estimate of the transition tax and ancillary effects. The provisional estimate of transition tax includes state taxes and foreign withholding taxes related to the change in the Company's indefinite reinvestment assertion with respect to its pre-2018 foreign earnings. The Company previously considered most unremitted earnings of its non-U.S. subsidiaries, except amounts repatriated in the year earned, to be permanently reinvested and, accordingly, recorded no deferred U.S. income taxes on such earnings. The Company has initially analyzed its global capital requirements and potential tax liabilities attributable to repatriation. The Company estimates that it will repatriate $3.4 billion that was previously considered indefinitely invested. Included in the $240 million charge in 2017 is a $53 million provisional estimate for withholding and state income taxes. In addition, reducing the U.S. corporate tax rate from 35% to 21% and the change in deductibility of certain compensation awards to certain executive officers of the Company effective on January 1, 2018, resulted in a net charge of $220 million in the fourth quarter of 2017 to reduce the value of our U.S. deferred tax assets and liabilities. Adjustments during the first half of 2018 to provisional estimates of transition taxes and U.S. deferred tax assets and liabilities increased income tax expense by $3 million . These estimates may be further adjusted during 2018 when the Company has finalized its analysis of all the relevant information. In December of 2017, the SEC issued Staff Accounting Bulletin 118 ("SAB 118"), establishing a one-yea r measurement period to complete the accounting for the income tax effects of the TCJA. SAB 118 anticipates three alternative states of completion at the end of the reporting period of accounting for these effects: (1) the tax accounting work has been completed with respect to an item; (2) a provisional amount has been recognized because a reasonable estimate was possible, or (3) a reasonable estimate cannot be provided. The Company believes its analysis of the TCJA to date provides an appropriate basis to record a provisional estimate. Our provisional estimates include the effects of the deemed repatriation tax and the Company's position with respect to permanently reinvested earnings, the impact of the Global Intangible Low Taxed Income ("GILTI") provision and the remeasurement of U.S. deferred tax based on estimated enactment-date deferred tax balances, which may be adjusted in 2018 when the 2017 tax return is filed. TCJA’s transition tax requires detailed calculations of current and accumulated taxable earnings at the level of each foreign subsidiary, computed in functional currency at the greater of two alternative measurement dates and converted into U.S. dollars. In preparing its 2017 U.S. federal return the Company is performing these calculations for approximately seven hundred foreign subsidiaries. In the third quarter management expects to update its estimate of the transition tax, its global permanent investment strategy, and the impact on U.S. deferred tax assets from the change in tax rate. However, given the significant complexity of the TCJA and still-anticipated guidance from the U.S. Treasury about its implementation, these estimates may be further adjusted during the fourth quarter. 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.
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). The Company does not have any assets or liabilities that are measured using Level 2 inputs. 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. Liabilities measured using Level 3 inputs include liabilities for contingent purchase consideration. Valuation Techniques Equity Securities, Money Market Funds and Mutual Funds – Level 1 Investments for which market quotations are readily available are valued at the sale price on their principal exchange or, for certain markets, official closing bid price. Money market funds are valued using a valuation technique that results in price per share at $1.00 . Contingent Purchase Consideration Liability – Level 3 Purchase consideration for some acquisitions made by the Company includes 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 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 entities.
New Accounting Pronouncements	New Accounting Guidance 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: New Revenue Recognition Standard 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 Company elected to apply the modified retrospective method to all contracts. The guidance includes requirements to estimate variable or contingent consideration to be received, which will result in revenue being recognized earlier than under legacy GAAP. In addition, the guidance requires the capitalization and amortization of certain costs which were expensed as incurred under legacy GAAP. As discussed in more detail below, the adoption of this new revenue recognition standard will shift revenue among quarters from historical patterns, but is not expected to have a significant year-over-year impact on annual revenue. Upon adoption of the new revenue standard, the Company recognized significant movement in the quarterly timing of revenue recognized in the Risk and Insurance Services segment. In particular, under the new standard the recognition of revenue for reinsurance broking was accelerated from historical patterns. Estimated revenue from these treaties is recognized largely at the policy effective date at which point control over the services provided by the Company transfers to the client and the client has accepted the services. This resulted in a significant increase in revenue in the first quarter of 2018 compared to the same period in 2017. Prior to the adoption of this standard, revenue related to most reinsurance placements was recognized on the later of billing or effective date as premiums are determined by the primary insurers and attached to the reinsurance treaties. Typically, this resulted in revenue being recognized over a 12 to 18 month period. The timing of revenue recognition for certain fee based brokerage arrangements will shift among quarters. However, since the vast majority of the Company's fee arrangements involve contracts that cover a single year of services, the Company does not expect there will be a significant change in the amount of revenue recognized in an annual period. In the Risk and Insurance Services segment, certain pre-placement costs are now deferred and amortized into earnings when revenue from the placement is recognized. These costs were previously expensed as incurred. As such, the Company expects the recognition of costs to shift among quarters. In the Consulting segment, the adoption of the new revenue standard will not have a significant impact on the timing of revenue recognition in quarterly or annual periods. In Consulting, the Company incurs implementation costs necessary to facilitate the delivery of the contracted services. The Company has concluded that certain additional implementation costs previously expensed under legacy GAAP will be deferred under the new guidance. In addition, the amortization period for these implementation costs will include the initial contract term plus expected renewals. 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. The comparative prior period information was not restated and will continue to be reported under the legacy accounting standards that were in effect for those periods. The impact of adoption of the new revenue standard on the Company's consolidated income statement was as follows (in millions): Three Months Ended June 30, Six Months Ended June 30, Revenue Standard Impact Legacy GAAP As Reported Revenue Standard Impact Legacy GAAP Revenue $ 3,734 $ (24 ) $ 3,710 $ 7,734 $ (185 ) $ 7,549 Expense: Compensation and Benefits 2,135 (10 ) 2,125 4,359 (70 ) 4,289 Other Operating Expenses 908 — 908 1,776 — 1,776 Operating Expenses 3,043 (10 ) 3,033 6,135 (70 ) 6,065 Operating Income 691 (14 ) 677 1,599 (115 ) 1,484 Other Net Benefit Credits 65 — 65 131 — 131 Interest Income 3 — 3 6 — 6 Interest Expense (68 ) — (68 ) (129 ) — (129 ) Investment Income 28 — 28 28 — 28 Income Before Income Taxes 719 (14 ) 705 1,635 (115 ) 1,520 Income Tax Expense 183 (4 ) 179 403 (30 ) 373 Net Income Before Non-Controlling Interests 536 (10 ) 526 1,232 (85 ) 1,147 Less: Net Income Attributable to Non-Controlling Interests 5 — 5 11 — 11 Net Income Attributable to the Company $ 531 $ (10 ) $ 521 $ 1,221 $ (85 ) $ 1,136 The impact of adoption of the new revenue standard on the Company's consolidated balance sheet was as follows (in millions): June 30, 2018 As Reported Revenue Standard Impact Legacy GAAP ASSETS Current assets: Cash and cash equivalents $ 1,036 $ — $ 1,036 Net receivables 4,601 (254 ) 4,347 Other current assets 538 (298 ) 240 Total current assets 6,175 (552 ) 5,623 Goodwill and intangible assets 10,411 — 10,411 Fixed assets, net 698 — 698 Pension related assets 1,808 — 1,808 Deferred tax assets 532 133 665 Other assets 1,535 (230 ) 1,305 TOTAL ASSETS $ 21,159 $ (649 ) $ 20,510 LIABILITIES AND EQUITY Current liabilities: Short-term debt $ 439 $ — $ 439 Accounts payable and accrued liabilities 2,246 (177 ) 2,069 Accrued compensation and employee benefits 1,103 — 1,103 Accrued income taxes 216 — 216 Dividends payable 212 — 212 Total current liabilities 4,216 (177 ) 4,039 Fiduciary liabilities 5,118 — 5,118 Less - cash and investments held in a fiduciary capacity (5,118 ) — (5,118 ) — — — Long-term debt 5,813 — 5,813 Pension, post-retirement and post-employment benefits 1,768 — 1,768 Liabilities for errors and omissions 303 — 303 Other liabilities 1,262 (23 ) 1,239 Total equity 7,797 (449 ) 7,348 TOTAL LIABILITIES AND EQUITY $ 21,159 $ (649 ) $ 20,510 The impact of adoption of the new revenue standard on the Company's consolidated statement of cash flow was as follows (in millions): Six Months Ended June 30, 2018 As Reported Revenue Standard Impact Legacy GAAP Operating cash flows: Net income before non-controlling interests $ 1,232 $ (85 ) $ 1,147 Adjustments to reconcile net income to cash provided by operations: Depreciation and amortization of fixed assets and capitalized software 159 — 159 Amortization of intangible assets 88 — 88 Adjustments and payments related to contingent consideration liability 2 — 2 Provision for deferred income taxes 34 — 34 Gain on investments (28 ) — (28 ) Gain on disposition of assets (1 ) — (1 ) Share-based compensation expense 99 — 99 Changes in assets and liabilities: Net receivables (388 ) 186 (202 ) Other current assets 4 (20 ) (16 ) Other assets (10 ) (26 ) (36 ) Accounts payable and accrued liabilities 30 (55 ) (25 ) Accrued compensation and employee benefits (614 ) — (614 ) Accrued income taxes 18 — 18 Contributions to pension excess of expense/credit (178 ) — (178 ) Other liabilities (10 ) — (10 ) Effect of exchange rate changes (24 ) — (24 ) Net cash provided by operations $ 413 $ — $ 413 The adoption of the revenue recognition standard did not have an impact on the Company's financing or investing cash flows. Other Standards Adopted Effective January 1, 2018 using the modified retrospective approach 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 new guidance was effective for public companies for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. The Company holds certain equity investments that under legacy GAAP were previously treated as available for sale securities, whereby the mark-to-market change was recorded to other comprehensive income in its consolidated balance sheet. 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. Therefore, prior periods have not been restated. 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. The impact on the Company's balance sheet as of January 1, 2018 related to the adoption of the accounting standards using the modified retrospective approach as discussed above is as follows: Adjustments Balance at December 31, 2017 Revenue Recognition Financial Instruments Intra-Entity Transfer Balance at January 1, 2018 Balance Sheet Assets Net Receivables $ 4,133 $ 68 $ — $ — $ 4,201 Other Current Assets 224 318 — — 542 Other Assets 1,430 226 — — 1,656 Deferred Tax Assets 669 (103 ) — (14 ) 552 Liabilities Accounts Payable and Accrued Liabilities 2,083 122 — — 2,205 Other Liabilities 1,311 23 — — 1,334 Equity Other Accumulated Comprehensive Income — — (14 ) — (14 ) Retained Earnings $ 13,140 $ 364 $ 14 $ (14 ) $ 13,504 Cumulative effect adjustment related to the adoption of the revenue recognition standard The cumulative effect adjustment recorded to net receivables is primarily related to contingent brokerage revenue and reinsurance revenue placements. Under the new guidance, the Company is required to record an estimate of variable or contingent consideration earlier than under the previous rules. Also under the new guidance, revenue related to most reinsurance placements is accelerated versus previous patterns. The cumulative effect adjustments also includes the capitalization of costs to fulfill and costs to obtain that are included in other current assets and other assets, respectively. These costs were previously expensed as incurred. The adjustment to accounts payable and accrued liabilities includes deferred revenue related to the timing of fee revenue recognition for fee based arrangements and certain post placement servicing costs, primarily related to reinsurance brokerage costs that were previously expensed as incurred. Adoption of amended accounting standard using the retrospective application approach Effective January 1, 2018, the Company adopted new guidance that changes the presentation of net periodic pension cost and net periodic postretirement cost (''net periodic benefit costs"). The new guidance requires employers to report the service cost component of net periodic benefit costs in the same line item as other compensation costs in the income statement. The other components of net periodic benefit costs are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The new guidance requires retrospective application for the presentation of the service cost component and the other components of net periodic benefit costs. Accordingly, we have reclassified prior period information in the consolidated results of operations, segment data and related disclosures contained in our management's discussion and analysis and notes to the consolidated financial statements to reflect the retrospective adoption of this standard. Other accounting standards adopted effective January 1, 2018 In November 2016, the FASB issued new guidance which requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. As a result, amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. The Company adopted this guidance, which is required to be applied retrospectively to all periods presented, effective January 1, 2018. The adoption of this guidance did not impact the Company's consolidated balance sheets or consolidated statements of cash flows. In August 2016, the FASB issued new guidance which adds or clarifies guidance on the classification of certain cash receipts and payments in the statement of cash flows, including cash payments for debt prepayments or debt extinguishment costs, contingent consideration payments made after a business combination and distributions received from equity method investees. The Company adopted this guidance effective January 1, 2018. The adoption of this guidance did not impact the Company's consolidated statements of cash flows. In January 2017, the FASB issued guidance which clarifies the definition of a business in order to assist companies with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. The Company adopted this guidance effective January 1, 2018. The adoption of this standard did not have an impact on the Company's financial position or results of operations. New Accounting Pronouncements Not Yet Adopted 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 February 2016, the FASB issued new guidance intended to improve financial reporting for leases. Under the new guidance, a lessee will be required to recognize assets and liabilities for leases with lease terms of more than 12 months. Consistent with current GAAP, the recognition, measurement, and presentation of expenses and cash flows arising from a lease by a lessee primarily will depend on its classification as a financing or operating lease. However, unlike current GAAP, which requires that only capital leases be recognized on the balance sheet, the new guidance requires that both types of leases be recognized on the balance sheet. The new guidance will require additional disclosures to help investors and other financial statement users better understand the amount, timing, and uncertainty of cash flows arising from leases. These disclosures include qualitative and quantitative requirements, and additional information about the amounts recorded in the financial statements. The accounting by organizations that own the assets ("lessor") leased by the lessee will remain largely unchanged from current GAAP. However, the guidance contains targeted improvements that are intended to align, where necessary, lessor accounting with the lessee accounting model. The new guidance on leases is effective for public companies for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early application is permitted. The Company is currently evaluating the impact the adoption of the guidance will have on its financial position and results of operations, but expects material "right of use" assets and lease liabilities to be recorded on its consolidated balance sheets.

Revenue (Tables)

Revenue (Tables)	6 Months Ended
	Jun. 30, 2018
Revenue from Contract with Customer [Abstract]
Disaggregation of Revenue	The following schedule disaggregates various components of the Company's revenue: Three Months Ended Six Months Ended 2018 2018 Marsh: EMEA $ 526 $ 1,169 Asia Pacific 183 347 Latin America 99 183 Total International 808 1,699 U.S./Canada 941 1,744 Total Marsh 1,749 3,443 Guy Carpenter 332 969 Subtotal 2,081 4,412 Fiduciary interest income 15 28 Total Risk and Insurance Services $ 2,096 $ 4,440 Mercer: Defined Benefit Consulting & Administration $ 320 $ 659 Investment Management & Related Services 232 458 Total Wealth 552 1,117 Health 429 871 Career 177 341 Total Mercer 1,158 2,329 Oliver Wyman 492 989 Total Consulting $ 1,650 $ 3,318
Contract with Customer, Asset and Liability	The following schedule provides contract assets and contract liabilities information from contracts with customers. (In millions) January 1, 2018 June 30, 2018 Contract Assets $ 128 $ 178 Contract Liabilities $ 583 $ 647

Per Share Data (Tables)

Per Share Data (Tables)	6 Months Ended
	Jun. 30, 2018
Earnings Per Share [Abstract]
Diluted EPS Calculation Continuing Operations	Basic net income per share attributable to the Company is calculated by dividing the after-tax income attributable to the Company by the weighted average number of outstanding shares of the Company’s common stock. Diluted net income per share attributable to the Company is calculated by dividing the after-tax income attributable to the Company by the weighted average number of outstanding shares of the Company’s common stock, which have been adjusted for the dilutive effect of potentially issuable common shares. Basic and Diluted EPS Calculation Three Months Ended Six Months Ended (In millions, except per share amounts) 2018 2017 2018 2017 Net income before non-controlling interests $ 536 $ 507 $ 1,232 $ 1,085 Less: Net income attributable to non-controlling interests 5 6 11 15 Net income attributable to the Company $ 531 $ 501 $ 1,221 $ 1,070 Basic weighted average common shares outstanding 507 514 507 514 Dilutive effect of potentially issuable common shares 5 6 6 7 Diluted weighted average common shares outstanding 512 520 513 521 Average stock price used to calculate common stock equivalents $ 81.64 $ 75.41 $ 82.24 $ 73.36

Supplemental Disclosures to t29

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Tables)	6 Months Ended
	Jun. 30, 2018
Supplemental Cash Flow Information [Abstract]
Additional Information Concerning Acquisitions, Interest and Income Taxes Paid	The following schedule provides additional information concerning acquisitions, interest and income taxes paid for the six-month periods ended June 30, 2018 and 2017 . (In millions) 2018 2017 Assets acquired, excluding cash $ 204 $ 576 Liabilities assumed (28 ) (74 ) Contingent/deferred purchase consideration (32 ) (90 ) Net cash outflow for current year acquisitions $ 144 $ 412 (In millions) 2018 2017 Interest paid $ 107 $ 92 Income taxes paid, net of refunds $ 349 $ 297

Other Comprehensive Income (L30

Other Comprehensive Income (Loss) (Tables)	6 Months Ended
	Jun. 30, 2018
Equity [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss)	The changes, net of tax, in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the three and six -month period ended June 30, 2018 and 2017 , 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 April 1, 2018 $ — $ (2,963 ) $ (942 ) $ (3,905 ) Other comprehensive income (loss) before reclassifications — 129 (516 ) (387 ) Amounts reclassified from accumulated other comprehensive income — 27 — 27 Net current period other comprehensive income (loss) — 156 (516 ) (360 ) Balance as of June 30, 2018 $ — $ (2,807 ) $ (1,458 ) $ (4,265 ) (In millions) Unrealized Investment Gains Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of April 1, 2017 $ 16 $ (3,208 ) $ (1,645 ) $ (4,837 ) Other comprehensive income (loss) before reclassifications 14 (40 ) 289 263 Amounts reclassified from accumulated other comprehensive income — 33 — 33 Net current period other comprehensive income (loss) 14 (7 ) 289 296 Balance as of June 30, 2017 $ 30 $ (3,215 ) $ (1,356 ) $ (4,541 ) (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 — 29 (293 ) (264 ) Amounts reclassified from accumulated other comprehensive income — 56 — 56 Net current period other comprehensive income (loss) — 85 (293 ) (208 ) Balance as of June 30, 2018 $ — $ (2,807 ) $ (1,458 ) $ (4,265 ) (In millions) Unrealized Investment Gains Pension/Post-Retirement Plans Gains (Losses) Foreign Currency Translation Gains (Losses) Total Gains (Losses) Balance as of December 31, 2016 $ 19 $ (3,232 ) $ (1,880 ) $ (5,093 ) Other comprehensive income (loss) before reclassifications 11 (46 ) 524 489 Amounts reclassified from accumulated other comprehensive income — 63 — 63 Net current period other comprehensive income (loss) 11 17 524 552 Balance as of June 30, 2017 $ 30 $ (3,215 ) $ (1,356 ) $ (4,541 )
Schedule of Components of Comprehensive Income (Loss)	The components of other comprehensive income (loss) for the three and six -month period ended June 30, 2018 and 2017 are as follows: Three Months Ended June 30, 2018 2017 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (529 ) $ (13 ) $ (516 ) $ 290 $ 1 $ 289 Unrealized investment gains — — — 24 10 14 Pension/post-retirement plans: Amortization of losses included in net periodic pension cost: Prior service credits (a) (1 ) — (1 ) — — — Net actuarial losses (a) 37 9 28 42 9 33 Subtotal 36 9 27 42 9 33 Effect of remeasurement — — — — 1 (1 ) Foreign currency translation adjustments 156 27 129 (47 ) (8 ) (39 ) Pension/post-retirement plans gains (losses) 192 36 156 (5 ) 2 (7 ) Other comprehensive (loss) income $ (337 ) $ 23 $ (360 ) $ 309 $ 13 $ 296 (a) Components of net periodic pension cost are included in compensation and benefits in the consolidated statements of income. Income tax credits on prior service costs and net actuarial losses are included in income tax expense. Six Months Ended June 30, 2018 2017 (In millions) Pre-Tax Tax (Credit) Net of Tax Pre-Tax Tax (Credit) Net of Tax Foreign currency translation adjustments $ (301 ) $ (8 ) $ (293 ) $ 525 $ 1 $ 524 Unrealized investment gains — — — 19 8 11 Pension/post-retirement plans: Amortization of losses included in net periodic pension cost: Prior service credits (a) (2 ) — (2 ) — — — Net actuarial losses (a) 74 16 58 82 19 63 Subtotal 72 16 56 82 19 63 Effect of remeasurement — — — 9 3 6 Effect of curtailment — — — (1 ) — (1 ) Effect of settlement — — — 1 — 1 Foreign currency translation adjustments 36 7 29 (62 ) (11 ) (51 ) Other — — — (1 ) — (1 ) Pension/post-retirement plans gains 108 23 85 28 11 17 Other comprehensive (loss) income $ (193 ) $ 15 $ (208 ) $ 572 $ 20 $ 552 (a) Components of net periodic pension cost are included in other net benefit credits in the consolidated statements of income. Tax on prior service costs and net actuarial losses is included in income tax expense.

Acquisitions (Tables)

Acquisitions (Tables)	6 Months Ended
	Jun. 30, 2018
Business Combinations [Abstract]
Schedule For Allocation of Acquisition Costs	The following table presents the preliminary allocation of the acquisition cost to the assets acquired and liabilities assumed during 2018 based on their fair values: For the Six Months Ended June 30, 2018 (In millions) Cash $ 160 Estimated fair value of deferred/contingent consideration 32 Total Consideration $ 192 Allocation of purchase price: Cash and cash equivalents $ 16 Accounts receivable, net 12 Property, plant, and equipment 3 Other intangible assets 73 Goodwill 116 Total assets acquired 220 Current liabilities 10 Other liabilities 18 Total liabilities assumed 28 Net assets acquired $ 192
Schedule of Acquired Finite-Lived Intangible Assets by Major Class	The following chart provides information about other intangible assets acquired during 2018 : Amount Weighted Average Amortization Period Client relationships $ 72 9 years Other 1 4 years $ 73
Pro-Forma Information	The unaudited pro-forma financial data is presented for illustrative purposes only and is not necessarily indicative of the operating results that would have been achieved if such acquisitions had occurred on the dates indicated, nor is it necessarily indicative of future consolidated results. Three Months Ended Six Months Ended (In millions, except per share figures) 2018 2017 2018 2017 Revenue $ 3,748 $ 3,539 $ 7,770 $ 7,098 Net income attributable to the Company $ 532 $ 503 $ 1,225 $ 1,072 Basic net income per share attributable to the Company $ 1.05 $ 0.98 $ 2.41 $ 2.08 Diluted net income per share attributable to the Company $ 1.04 $ 0.97 $ 2.39 $ 2.06

Goodwill and Other Intangibles

Goodwill and Other Intangibles (Tables)	6 Months Ended
	Jun. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Changes in the Carrying Amount of Goodwill	Changes in the carrying amount of goodwill are as follows: June 30, (In millions) 2018 2017 Balance as of January 1, $ 9,089 $ 8,369 Goodwill acquired 116 370 Other adjustments (a) (28 ) 82 Balance at June 30, $ 9,177 $ 8,821
Amortized Intangible Assets	The gross cost and accumulated amortization at June 30, 2018 and December 31, 2017 are as follows: June 30, 2018 December 31, 2017 (In millions) Gross Cost Accumulated Amortization Net Carrying Amount Gross Cost Accumulated Amortization Net Carrying Amount Client Relationships $ 1,711 $ 580 $ 1,131 $ 1,672 $ 518 $ 1,154 Other (a) 237 134 103 234 114 120 Amortized intangibles $ 1,948 $ 714 $ 1,234 $ 1,906 $ 632 $ 1,274 (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 2018 (excludes amortization through June 30, 2018) $ 94 2019 173 2020 154 2021 143 2022 132 Subsequent years 538 $ 1,234

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2018
Fair Value Disclosures [Abstract]
Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following fair value hierarchy table presents information about the Company’s assets and liabilities measured at fair value on a recurring basis as of June 30, 2018 and December 31, 2017 . Identical Assets (Level 1) Observable Inputs (Level 2) Unobservable Inputs (Level 3) Total (In millions) 06/30/18 12/31/17 06/30/18 12/31/17 06/30/18 12/31/17 06/30/18 12/31/17 Assets: Financial instruments owned: Exchange traded equity securities (a) $ 99 $ 81 $ — $ — $ — $ — $ 99 $ 81 Mutual funds (a) 144 158 — — — — 144 158 Money market funds (b) 33 143 — — — — 33 143 Total assets measured at fair value $ 276 $ 382 $ — $ — $ — $ — $ 276 $ 382 Fiduciary Assets: Money market funds $ 129 $ 111 $ — $ — $ — $ — $ 129 $ 111 Total fiduciary assets measured at fair value $ 129 $ 111 $ — $ — $ — $ — $ 129 $ 111 Liabilities: Contingent purchase consideration liability (c) $ — $ — $ — $ — $ 185 $ 189 $ 185 $ 189 Total liabilities measured at fair value $ — $ — $ — $ — $ 185 $ 189 $ 185 $ 189 (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 six month periods ending June 30, 2018 and 2017 that represent contingent consideration related to acquisitions: Three Months Ended Six Months Ended (In millions) 2018 2017 2018 2017 Balance at beginning of period, $ 161 $ 247 $ 189 $ 241 Additions 20 — 26 34 Payments (1 ) (53 ) (41 ) (65 ) Revaluation Impact 6 8 11 (8 ) Other (a) (1 ) 1 — 1 Balance at June 30, $ 185 $ 203 $ 185 $ 203 (a) Primarily reflects the impact of foreign exchange.

Retirement Benefits (Tables)

Retirement Benefits (Tables)	6 Months Ended
	Jun. 30, 2018
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 June 30, (In millions) 2018 2017 2018 2017 Service cost $ 7 $ 19 $ — $ — Interest cost 117 124 1 1 Expected return on plan assets (218 ) (230 ) — — Amortization of prior service cost (1 ) (1 ) (1 ) — Recognized actuarial loss 37 43 — — Net periodic benefit (credit) cost $ (58 ) $ (45 ) $ — $ 1 Combined U.S. and significant non-U.S. plans Pension Benefits Post-retirement Benefits For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 17 $ 37 $ — $ — Interest cost 235 246 2 2 Expected return on plan assets (439 ) (454 ) — — Amortization of prior service (credit) cost (1 ) (1 ) (2 ) 1 Recognized actuarial loss 74 83 — — Net periodic benefit (credit) cost $ (114 ) $ (89 ) $ — $ 3 Curtailment gain — (1 ) — — Settlement loss — 1 — — Total (credit) cost $ (114 ) $ (89 ) $ — $ 3 As discussed in Note 17, effective January 1, 2018, the Company adopted the new guidance that changes the presentation of net periodic pension cost and net periodic postretirement cost (''net periodic benefit costs"). The new guidance requires employers to report the service cost component of net periodic benefit costs in the same line item as other compensation costs in the income statement. The other components of net periodic benefit costs are required to be presented in the income statement separately from the service cost component and outside a subtotal of income from operations. The new guidance requires retrospective application for the presentation of the service cost component and the other components of net periodic benefit costs. Accordingly, the Company has reclassified prior period information in the following chart to conform with the current year's presentation: Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. plans Pension Post-retirement For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Compensation and benefits expense (Operating income) $ 7 $ 19 $ — $ — Other net benefit credits (65 ) (64 ) — 1 Total (credit) cost $ (58 ) $ (45 ) $ — $ 1 Amounts Recorded in the Consolidated Statement of Income Combined U.S. and significant non-U.S. plans Pension Post-retirement For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Compensation and benefits expense (Operating income) $ 17 $ 37 $ — $ — Other net benefit credits (131 ) (126 ) — 3 Total (credit) cost $ (114 ) $ (89 ) $ — $ 3 U.S. Plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ — $ — $ — $ — Interest cost 59 66 1 1 Expected return on plan assets (90 ) (90 ) — — Amortization of prior service (credit) cost — — (1 ) 1 Recognized actuarial loss (gain) 14 10 — (1 ) Net periodic benefit (credit) cost $ (17 ) $ (14 ) $ — $ 1 U.S. Plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ — $ — $ — $ — Interest cost 118 132 1 1 Expected return on plan assets (179 ) (179 ) — — Amortization of prior service (credit) cost — — (1 ) 2 Recognized actuarial loss (gain) 27 19 — (1 ) Net periodic benefit (credit) cost $ (34 ) $ (28 ) $ — $ 2 Significant non-U.S. plans only Pension Post-retirement For the Three Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 7 $ 19 $ — $ — Interest cost 58 58 — — Expected return on plan assets (128 ) (140 ) — — Amortization of prior service cost (1 ) (1 ) — (1 ) Recognized actuarial loss 23 33 — 1 Net periodic benefit (credit) cost $ (41 ) $ (31 ) $ — $ — Significant non-U.S. plans only Pension Post-retirement For the Six Months Ended June 30, (In millions) 2018 2017 2018 2017 Service cost $ 17 $ 37 $ — $ — Interest cost 117 114 1 1 Expected return on plan assets (260 ) (275 ) — — Amortization of prior service credit (1 ) (1 ) (1 ) (1 ) Recognized actuarial loss 47 64 — 1 Net periodic benefit (credit) cost $ (80 ) $ (61 ) $ — $ 1 Curtailment gain — (1 ) — — Settlement loss — 1 — — Total (credit) cost $ (80 ) $ (61 ) $ — $ 1
Schedule of Assumptions Used	The weighted average actuarial assumptions utilized to calculate the net periodic benefit costs for the U.S. and significant non-U.S. defined benefit plans are as follows: Combined U.S. and significant non-U.S. plans Pension Post-retirement June 30, 2018 2017 2018 2017 Weighted average assumptions: Expected return on plan assets 5.83 % 6.64 % — — Discount Rate 3.07 % 3.40 % 3.21 % 3.64 % Rate of compensation increase 1.73 % 1.77 % — —

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2018
Debt Disclosure [Abstract]
Schedule of Outstanding Debt	The Company’s outstanding debt is as follows: (In millions) June 30, December 31, Short-term: Commercial paper $ 175 $ — Current portion of long-term debt 264 262 439 262 Long-term: Senior notes – 2.55% due 2018 250 250 Senior notes – 2.35% due 2019 299 299 Senior notes – 2.35% due 2020 499 498 Senior notes – 4.80% due 2021 498 498 Senior notes – 2.75% due 2022 497 496 Senior notes – 3.30% due 2023 348 348 Senior notes – 4.05% due 2023 248 248 Senior notes – 3.50% due 2024 597 596 Senior notes – 3.50% due 2025 496 496 Senior notes – 3.75% due 2026 596 596 Senior notes – 5.875% due 2033 297 297 Senior notes – 4.35% due 2047 492 492 Senior notes – 4.20% due 2048 592 — Mortgage – 5.70% due 2035 364 370 Other 4 3 6,077 5,487 Less current portion 264 262 $ 5,813 $ 5,225
Estimated Fair Value Of Significant Financial Instruments	The estimated fair value of the Company’s short-term and long-term debt is provided below. Certain estimates and judgments were required to develop the fair value amounts. The fair value amounts shown below are not necessarily indicative of the amounts that the Company would realize upon disposition, nor do they indicate the Company’s intent or need to dispose of the financial instrument. June 30, 2018 December 31, 2017 (In millions) Carrying Amount Fair Value Carrying Amount Fair Value Short-term debt $ 439 $ 440 $ 262 $ 264 Long-term debt $ 5,813 $ 5,826 $ 5,225 $ 5,444

Restructuring Costs (Tables)

Restructuring Costs (Tables)	6 Months Ended
	Jun. 30, 2018
Restructuring and Related Activities [Abstract]
Restructuring Activities	Details of the restructuring activity from January 1, 2017 through June 30, 2018 , which includes liabilities from actions prior to 2018 , are as follows: (In millions) Liability at 1/1/17 Amounts Accrued Cash Paid Other Liability at 12/31/17 Amounts Accrued Cash Paid Other Liability at 6/30/18 Severance $ 32 $ 31 $ (49 ) $ 1 $ 15 $ 51 $ (22 ) $ (1 ) $ 43 Future rent under non-cancelable leases and other costs 61 9 (22 ) 2 50 13 (19 ) — 44 Total $ 93 $ 40 $ (71 ) $ 3 $ 65 $ 64 $ (41 ) $ (1 ) $ 87

Segment Information (Tables)

Segment Information (Tables)	6 Months Ended
	Jun. 30, 2018
Segment Reporting [Abstract]
Selected Information And Details For MMC's Operating Segments	Selected information about the Company’s operating segments for the three and six -month periods ended June 30, 2018 and 2017 are as follows: Three Months Ended Six Months Ended (In millions) Revenue Operating Income (Loss) Revenue Operating Income (Loss) 2018– Risk and Insurance Services $ 2,096 (a) $ 472 $ 4,440 (c) $ 1,188 Consulting 1,650 (b) 267 3,318 (d) 514 Total Operating Segments 3,746 739 7,758 1,702 Corporate / Eliminations (12 ) (48 ) (24 ) (103 ) Total Consolidated $ 3,734 $ 691 $ 7,734 $ 1,599 2017– Risk and Insurance Services $ 1,916 (a) $ 482 $ 3,905 (c) $ 1,050 Consulting 1,592 (b) 265 3,118 (d) 490 Total Operating Segments 3,508 747 7,023 1,540 Corporate / Eliminations (13 ) (46 ) (25 ) (90 ) Total Consolidated $ 3,495 $ 701 $ 6,998 $ 1,450 (a) Includes inter-segment revenue of $4 million in 2017 , interest income on fiduciary funds of $15 million and $9 million in 2018 and 2017 , respectively, and equity method income of $7 million in both 2018 and 2017 . (b) Includes inter-segment revenue of $12 million and $9 million in 2018 and 2017 , respectively, interest income on fiduciary funds of $1 million and less than $1 million in 2018 and 2017 , respectively, and equity method income of $5 million in both 2018 and in 2017 . (c) Includes inter-segment revenue of $1 million and $4 million in 2018 and 2017 , respectively, interest income on fiduciary funds of $28 million and $17 million in 2018 and 2017 , respectively, and equity method income of $6 million and $9 million in 2018 and 2017 , respectively. (d) Includes inter-segment revenue of $23 million and $21 million in 2018 and 2017 , respectively, interest income on fiduciary funds of $2 million and $1 million in 2018 and 2017 , respectively, and equity method income of $8 million in 2018 and $9 million in 2017 , respectively.
Details of Operating Segment Revenue	Details of operating segment revenue for the three and six -month periods ended June 30, 2018 and 2017 are as follows: Three Months Ended Six Months Ended (In millions) 2018 2017 2018 2017 Risk and Insurance Services Marsh $ 1,760 $ 1,621 $ 3,463 $ 3,223 Guy Carpenter 336 295 977 682 Total Risk and Insurance Services 2,096 1,916 4,440 3,905 Consulting Mercer 1,158 1,109 2,329 2,186 Oliver Wyman Group 492 483 989 932 Total Consulting 1,650 1,592 3,318 3,118 Total Operating Segments 3,746 3,508 7,758 7,023 Corporate / Eliminations (12 ) (13 ) (24 ) (25 ) Total $ 3,734 $ 3,495 $ 7,734 $ 6,998

New Accounting Guidance (Tables

New Accounting Guidance (Tables)	6 Months Ended
	Jun. 30, 2018
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Schedule of New Accounting Pronouncements and Changes in Accounting Principles	The impact of adoption of the new revenue standard on the Company's consolidated income statement was as follows (in millions): Three Months Ended June 30, Six Months Ended June 30, Revenue Standard Impact Legacy GAAP As Reported Revenue Standard Impact Legacy GAAP Revenue $ 3,734 $ (24 ) $ 3,710 $ 7,734 $ (185 ) $ 7,549 Expense: Compensation and Benefits 2,135 (10 ) 2,125 4,359 (70 ) 4,289 Other Operating Expenses 908 — 908 1,776 — 1,776 Operating Expenses 3,043 (10 ) 3,033 6,135 (70 ) 6,065 Operating Income 691 (14 ) 677 1,599 (115 ) 1,484 Other Net Benefit Credits 65 — 65 131 — 131 Interest Income 3 — 3 6 — 6 Interest Expense (68 ) — (68 ) (129 ) — (129 ) Investment Income 28 — 28 28 — 28 Income Before Income Taxes 719 (14 ) 705 1,635 (115 ) 1,520 Income Tax Expense 183 (4 ) 179 403 (30 ) 373 Net Income Before Non-Controlling Interests 536 (10 ) 526 1,232 (85 ) 1,147 Less: Net Income Attributable to Non-Controlling Interests 5 — 5 11 — 11 Net Income Attributable to the Company $ 531 $ (10 ) $ 521 $ 1,221 $ (85 ) $ 1,136 The impact of adoption of the new revenue standard on the Company's consolidated balance sheet was as follows (in millions): June 30, 2018 As Reported Revenue Standard Impact Legacy GAAP ASSETS Current assets: Cash and cash equivalents $ 1,036 $ — $ 1,036 Net receivables 4,601 (254 ) 4,347 Other current assets 538 (298 ) 240 Total current assets 6,175 (552 ) 5,623 Goodwill and intangible assets 10,411 — 10,411 Fixed assets, net 698 — 698 Pension related assets 1,808 — 1,808 Deferred tax assets 532 133 665 Other assets 1,535 (230 ) 1,305 TOTAL ASSETS $ 21,159 $ (649 ) $ 20,510 LIABILITIES AND EQUITY Current liabilities: Short-term debt $ 439 $ — $ 439 Accounts payable and accrued liabilities 2,246 (177 ) 2,069 Accrued compensation and employee benefits 1,103 — 1,103 Accrued income taxes 216 — 216 Dividends payable 212 — 212 Total current liabilities 4,216 (177 ) 4,039 Fiduciary liabilities 5,118 — 5,118 Less - cash and investments held in a fiduciary capacity (5,118 ) — (5,118 ) — — — Long-term debt 5,813 — 5,813 Pension, post-retirement and post-employment benefits 1,768 — 1,768 Liabilities for errors and omissions 303 — 303 Other liabilities 1,262 (23 ) 1,239 Total equity 7,797 (449 ) 7,348 TOTAL LIABILITIES AND EQUITY $ 21,159 $ (649 ) $ 20,510 The impact of adoption of the new revenue standard on the Company's consolidated statement of cash flow was as follows (in millions): Six Months Ended June 30, 2018 As Reported Revenue Standard Impact Legacy GAAP Operating cash flows: Net income before non-controlling interests $ 1,232 $ (85 ) $ 1,147 Adjustments to reconcile net income to cash provided by operations: Depreciation and amortization of fixed assets and capitalized software 159 — 159 Amortization of intangible assets 88 — 88 Adjustments and payments related to contingent consideration liability 2 — 2 Provision for deferred income taxes 34 — 34 Gain on investments (28 ) — (28 ) Gain on disposition of assets (1 ) — (1 ) Share-based compensation expense 99 — 99 Changes in assets and liabilities: Net receivables (388 ) 186 (202 ) Other current assets 4 (20 ) (16 ) Other assets (10 ) (26 ) (36 ) Accounts payable and accrued liabilities 30 (55 ) (25 ) Accrued compensation and employee benefits (614 ) — (614 ) Accrued income taxes 18 — 18 Contributions to pension excess of expense/credit (178 ) — (178 ) Other liabilities (10 ) — (10 ) Effect of exchange rate changes (24 ) — (24 ) Net cash provided by operations $ 413 $ — $ 413 The adoption of the revenue recognition standard did not have an impact on the Company's financing or investing cash flows.
New Accounting Pronouncement, Early Adoption	The impact on the Company's balance sheet as of January 1, 2018 related to the adoption of the accounting standards using the modified retrospective approach as discussed above is as follows: Adjustments Balance at December 31, 2017 Revenue Recognition Financial Instruments Intra-Entity Transfer Balance at January 1, 2018 Balance Sheet Assets Net Receivables $ 4,133 $ 68 $ — $ — $ 4,201 Other Current Assets 224 318 — — 542 Other Assets 1,430 226 — — 1,656 Deferred Tax Assets 669 (103 ) — (14 ) 552 Liabilities Accounts Payable and Accrued Liabilities 2,083 122 — — 2,205 Other Liabilities 1,311 23 — — 1,334 Equity Other Accumulated Comprehensive Income — — (14 ) — (14 ) Retained Earnings $ 13,140 $ 364 $ 14 $ (14 ) $ 13,504

Nature of Operations (Details)

Nature of Operations (Details) $ in Billions	6 Months Ended
	Jun. 30, 2018USD ($)segment
Segment Reporting Information [Line Items]
Number of business segments | segment	2
Mercer Consulting Group
Segment Reporting Information [Line Items]
Assets under management | $	$ 240

Principles of Consolidation A40

Principles of Consolidation And Other Matters (Details)	3 Months Ended			6 Months Ended
	Jun. 30, 2018USD ($)	Dec. 31, 2017USD ($)discrete_charge	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)	Jun. 30, 2017	Jan. 01, 2018USD ($)
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$ 189,000,000			$ 189,000,000
Equity method investments lag period				3 months
Investment income	28,000,000		$ 5,000,000	$ 26,000,000
Equity method income	2,000,000			$ 9,000,000
Gains on equity investments	$ 19,000,000
Effective tax rate (as a percent)	25.60%		28.60%	24.70%	25.90%
Number of discrete charges | discrete_charge		2
Period for payable on undistributed earnings				8 years
Provisional income tax expense (benefit)				$ 240,000,000
Transition tax for accumulated foreign earnings, liability	$ 3,400,000,000			3,400,000,000
Provisional withholding and state income tax expense (benefit)				53,000,000
Change in tax rate, deferred tax asset, provisional income tax expense (benefit)				220,000,000
Increase to income tax expense (benefit)				3,000,000
Unrecognized tax benefits	72,000,000	$ 71,000,000		72,000,000
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	$ 8,000,000			$ 8,000,000
Retained Earnings
Significant Change in Unrecognized Tax Benefits is Reasonably Possible [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 14,000,000				$ 14,000,000

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	$ 14,131	$ 14,131	$ 13,504	$ 13,140
Contract with customer, asset, additions		215
Contract with customer, asset, reclassified to receivable		166
Contract with customer, liability, revenue recognized		334
Performance obligation satisfied in previous period		36
Capitalized contract cost, amortization	261	557
Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Retained earnings	364	$ 364	$ 364
Health Brokerage and Consulting
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer, percent		70.00%
Marsh Insurance Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation	48	$ 48
Mercer Consulting Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation	450	450
Oliver Wyman Group Consulting Group
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue, remaining performance obligation	2	2
Deferred Implementation Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost, net	39	39
Costs to Obtain
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost, net	196	196
Costs to Fulfill
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Capitalized contract cost, net	$ 154	$ 154

Revenue - Disaggregation of Rev

Revenue - Disaggregation of Revenue (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2018
Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 2,096	$ 4,440
Fiduciary interest income	15	28
Risk and Insurance Services Segment | EMEA
Disaggregation of Revenue [Line Items]
Revenue	526	1,169
Risk and Insurance Services Segment | Asia Pacific
Disaggregation of Revenue [Line Items]
Revenue	183	347
Risk and Insurance Services Segment | Latin America
Disaggregation of Revenue [Line Items]
Revenue	99	183
Risk and Insurance Services Segment | Total International
Disaggregation of Revenue [Line Items]
Revenue	808	1,699
Risk and Insurance Services Segment | U.S./Canada
Disaggregation of Revenue [Line Items]
Revenue	941	1,744
Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,650	3,318
Defined Benefit Consulting & Administration | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	320	659
Investment Management & Related Services | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	232	458
Total Wealth | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	552	1,117
Health | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	429
Career | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	177
Marsh Insurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	1,749	3,443
Guy Carpenter Reinsurance Group | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	332	969
Marsh & Guy Carpenter | Risk and Insurance Services Segment
Disaggregation of Revenue [Line Items]
Revenue	2,081	4,412
Mercer Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	1,158	2,329
Oliver Wyman Group Consulting Group | Consulting Segment
Disaggregation of Revenue [Line Items]
Revenue	$ 492	$ 989

Revenue - Contract Assets and C

Revenue - Contract Assets and Contract Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Contract Assets	$ 178	$ 128
Contract Liabilities	$ 647	$ 583

Revenue - Estimated Revenue Exp

Revenue - Estimated Revenue Expected to Be Recognized Related to Performance Obligations (Details) $ in Millions	Jun. 30, 2018USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-03-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 239
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-03-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	129
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-03-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	74
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-03-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	41
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-03-31
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, remaining performance obligation	$ 17

Fiduciary Assets and Liabilit45

Fiduciary Assets and Liabilities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Fiduciary Assets and Liabilities [Line Items]
Net uncollected premiums and claims receivable and payable	$ 8,300		$ 8,300		$ 6,800
Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds (less than)	15		28
Operating Segments | Risk and Insurance Services Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds (less than)	15	$ 9	28	$ 17
Operating Segments | Consulting Segment
Fiduciary Assets and Liabilities [Line Items]
Interest on fiduciary funds (less than)	$ 1	$ 1	$ 2	$ 1

Per Share Data (Basic and Dilut

Per Share Data (Basic and Diluted EPS Calculation Continuing Operations) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income before non-controlling interests	$ 536	$ 507	$ 1,232	$ 1,085
Less: Net income attributable to non-controlling interests	5	6	11	15
Net income attributable to the Company	$ 531	$ 501	$ 1,221	$ 1,070
Basic weighted average common shares outstanding (in shares)	507	514	507	514
Dilutive effect of potentially issuable common shares (in shares)	5	6	6	7
Diluted weighted average common shares outstanding (in shares)	512	520	513	521
Average stock price used to calculate common stock equivalents (in dollars per share)	$ 81.64	$ 75.41	$ 82.24	$ 73.36
Stock options outstanding (in shares)	10.5	12.4	10.5	12.4

Supplemental Disclosures to t47

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Additional Information Concerning Acquisitions, Interest And Income Taxes Paid) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Supplemental Cash Flow Information [Abstract]
Assets acquired, excluding cash	$ 204	$ 576
Liabilities assumed	(28)	(74)
Contingent/deferred purchase consideration	(32)	(90)
Net cash outflow for current year acquisitions	144	412
Interest paid	107	92
Income taxes paid, net of refunds	$ 349	$ 297

Supplemental Disclosures to t48

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items]
Deferred and contingent consideration from prior years acquisition	$ 85	$ 97
Contingent consideration from prior year's acquisitions	32	60
Net charge for adjustments related to acquisition related accounts	11	(8)
Payment of contingent consideration	9	5
Non-cash issuance of common stock	128	87
Stock-based compensation expense, equity awards	99	75
Prior Fiscal Periods Acquisitions
Supplemental Disclosure to the Consolidate Statements of Cash Flows [Line Items]
Deferred purchase consideration from prior years' acquisitions	53	37
Contingent consideration from prior year's acquisitions	$ 41	$ 65

Other Comprehensive Income (L49

Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive (loss) income, net of tax	$ (360)	$ 296	$ (208)	$ 552
Unrealized Investment Gains
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	0	16	14	19
Cumulative effect of new accounting principle in period of adoption					$ (14)
Other comprehensive income (loss) before reclassifications	0	14	0	11
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive (loss) income, net of tax	0	14	0	11
Balance, ending of period	0	30	0	30
Pension/Postretirement Plans Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(2,963)	(3,208)	(2,892)	(3,232)
Cumulative effect of new accounting principle in period of adoption					0
Other comprehensive income (loss) before reclassifications	129	(40)	29	(46)
Amounts reclassified from accumulated other comprehensive income	27	33	56	63
Other comprehensive (loss) income, net of tax	156	(7)	85	17
Balance, ending of period	(2,807)	(3,215)	(2,807)	(3,215)
Foreign Currency Translation Gains (Losses)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(942)	(1,645)	(1,165)	(1,880)
Cumulative effect of new accounting principle in period of adoption					0
Other comprehensive income (loss) before reclassifications	(516)	289	(293)	524
Amounts reclassified from accumulated other comprehensive income	0	0	0	0
Other comprehensive (loss) income, net of tax	(516)	289	(293)	524
Balance, ending of period	(1,458)	(1,356)	(1,458)	(1,356)
AOCI Attributable to Parent
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance, beginning of period	(3,905)	(4,837)	(4,043)	(5,093)
Cumulative effect of new accounting principle in period of adoption					$ (14)
Other comprehensive income (loss) before reclassifications	(387)	263	(264)	489
Amounts reclassified from accumulated other comprehensive income	27	33	56	63
Other comprehensive (loss) income, net of tax	(360)	296	(208)	552
Balance, ending of period	$ (4,265)	$ (4,541)	$ (4,265)	$ (4,541)

Other Comprehensive Income (L50

Other Comprehensive Income (Loss) (Schedule Of Components Of Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity [Abstract]
Foreign currency translation adjustments, Pre-Tax		$ (529)	$ 290	$ (301)	$ 525
Foreign currency translation adjustments, Tax		(13)	1	(8)	1
Foreign currency translation adjustments, Net of Tax		(516)	289	(293)	524
Unrealized investment gains (losses), Pre-Tax		0	24	0	19
Unrealized investment gains (losses), Tax		0	10	0	8
Unrealized investment gains (losses), Net of Tax		0	14	0	11
Pension/post-retirement plans:
Prior services credits, Pre-Tax	[1]	(1)	0	(2)	0
Prior service credits, Tax	[1]	0	0	0	0
Prior service credits, Net of Tax	[1]	(1)	0	(2)	0
Net actuarial loss, Pre-Tax	[1]	37	42	74	82
Net actuarial loss, Tax	[1]	9	9	16	19
Net actuarial loss, Net of Tax	[1]	28	33	58	63
Subtotal, Pre-Tax		36	42	72	82
Subtotal, Tax		9	9	16	19
Subtotal, Net of Tax		27	33	56	63
Effect of remeasurement, Pre-tax		0	0	0	9
Effect of remeasurement, Tax		0	1	0	3
Effect of remeasurement, Net of Tax		0	(1)	0	6
Effect of curtailment, Pre-Tax				0	(1)
Effect of curtailment, Tax				0	0
Effect of curtailment, Net of Tax				0	(1)
Effect of settlement, Pre-tax				0	1
Effect of settlement, Tax				0	0
Effect of settlement, Net of Tax				0	1
Foreign currency translation adjustment, Pre-Tax		156	(47)	36	(62)
Foreign currency translation adjustment, Tax		27	(8)	7	(11)
Foreign currency translation adjustment, Net of Tax		129	(39)	29	(51)
Other, Pre-Tax				0	(1)
Other, Tax				0	0
Other, Net of Tax				0	(1)
Pension/post-retirement plans (losses) gains, Pre-Tax		192	(5)	108	28
Pension/post-retirement plans (losses) gains, Tax		36	2	23	11
Pension/post-retirement plans (losses) gains, Net of Tax		156	(7)	85	17
Other comprehensive (loss) income, before tax		(337)	309	(193)	572
Other comprehensive income (loss), Tax		23	13	15	20
Other comprehensive (loss) income, net of tax		$ (360)	$ 296	$ (208)	$ 552
[1]	Components of net periodic pension cost are included in compensation and benefits in the Consolidated Statements of Income. Tax on prior service gains and net actuarial losses is included in income tax expense.

Acquisitions (Narrative) (Detai

Acquisitions (Narrative) (Details) $ in Millions	Jun. 25, 2018USD ($)colleague	Jun. 30, 2018USD ($)	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)acquisition	Jun. 30, 2017USD ($)	Dec. 31, 2017acquisition
Business Acquisition [Line Items]
Total consideration				$ 192	$ 510
Cash				160	420
Estimated fair value of deferred/contingent consideration				32	90
Contingent consideration from prior year's acquisitions				32	60
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Total consideration				192
Cash				160
Estimated fair value of deferred/contingent consideration				32
Revenue related to acquisitions		$ 11	$ 34	14	63
Operating (loss) income related to acquisitions		$ (1)	$ 5	(2)	15
Prior Fiscal Periods Acquisitions
Business Acquisition [Line Items]
Deferred purchase consideration from prior years' acquisitions				53	37
Contingent consideration from prior year's acquisitions				$ 41	$ 65
Wortham Insurance
Business Acquisition [Line Items]
Revenue	$ 130
Number of colleagues | colleague	530
Risk and Insurance Services Segment
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition				7		7
Consulting Segment
Business Acquisition [Line Items]
Number of acquisitions made (in acquisitions) | acquisition				5		3
Minimum
Business Acquisition [Line Items]
Revenue target period (in years)				2 years
Minimum | Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Revenue target period (in years)				2 years
Maximum
Business Acquisition [Line Items]
Revenue target period (in years)				4 years
Maximum | Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Revenue target period (in years)				4 years

Acquisitions (Allocation Of Acq

Acquisitions (Allocation Of Acquisition Costs) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Business Acquisition [Line Items]
Cash	$ 160	$ 420
Estimated fair value of deferred/contingent consideration	32	90
Total Consideration	192	510
Allocation of purchase price:
Goodwill	9,177	$ 8,821	$ 9,089	$ 8,369
Current Fiscal Period Acquisitions
Business Acquisition [Line Items]
Cash	160
Estimated fair value of deferred/contingent consideration	32
Total Consideration	192
Allocation of purchase price:
Cash and cash equivalents	16
Accounts receivable, net	12
Property, plant, and equipment	3
Other intangible assets	73
Goodwill	116
Total assets acquired	220
Current liabilities	10
Other liabilities	18
Total liabilities assumed	28
Net assets acquired	$ 192

Acquisitions (Acquired Finite-L

Acquisitions (Acquired Finite-Lived Intangible Assets) (Details) $ in Millions	6 Months Ended
	Jun. 30, 2018USD ($)
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 73
Client relationships
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 72
Finite-lived intangible assets, remaining amortization period	9 years
Other
Finite-Lived Intangible Assets [Line Items]
Finite-lived intangible assets acquired	$ 1
Finite-lived intangible assets, remaining amortization period	4 years

Acquisitions (Pro-Forma Informa

Acquisitions (Pro-Forma Information) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Business Combinations [Abstract]
Revenue	$ 3,748	$ 3,539	$ 7,770	$ 7,098
Net income attributable to the Company	$ 532	$ 503	$ 1,225	$ 1,072
Basic net income per share:
Basic net income per share attributable to the Company (in dollars per share)	$ 1.05	$ 0.98	$ 2.41	$ 2.08
Diluted net income per share:
Diluted net income per share attributable to the Company (in dollars per share)	$ 1.04	$ 0.97	$ 2.39	$ 2.06

Goodwill and Other Intangible55

Goodwill and Other Intangibles (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Goodwill	$ 9,177	$ 8,821	$ 9,089	$ 8,369
Aggregate amortization expense	88	$ 80
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Goodwill	6,500
Consulting Segment
Segment Reporting Information [Line Items]
Goodwill	$ 2,700

Goodwill and Other Intangible56

Goodwill and Other Intangibles (Changes in the Carrying Amount of Goodwill) (Details) - USD ($) $ in Millions		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017
Goodwill [Roll Forward]
Balance as of January 1,		$ 9,089	$ 8,369
Goodwill acquired		116	370
Other adjustments	[1]	(28)	82
Balance at June 30,		$ 9,177	$ 8,821
[1]	Primarily reflects the impact of foreign exchange.

Goodwill and Other Intangible57

Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Gross Cost		$ 1,948	$ 1,906
Accumulated Amortization		714	632
Net Carrying Amount		1,234	1,274
Client relationships
Finite-Lived Intangible Assets [Line Items]
Gross Cost		1,711	1,672
Accumulated Amortization		580	518
Net Carrying Amount		1,131	1,154
Other Intangible Assets
Finite-Lived Intangible Assets [Line Items]
Gross Cost	[1]	237	234
Accumulated Amortization	[1]	134	114
Net Carrying Amount	[1]	$ 103	$ 120
[1]	Primarily non-compete agreements, trade names and developed technology.

Goodwill And Other Intangible58

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
2018 (excludes amortization through June 30, 2018)	$ 94
2,019	173
2,020	154
2,021	143
2,022	132
Subsequent years	538
Net Carrying Amount	$ 1,234	$ 1,274

Fair Value Measurements (Narrat

Fair Value Measurements (Narrative) (Details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018USD ($)$ / sharesshares	Jun. 30, 2017USD ($)	Jun. 30, 2018USD ($)$ / sharesshares	Jun. 30, 2017USD ($)	Jun. 30, 2018R / shares	Dec. 31, 2017USD ($)	Dec. 31, 2014R / shares
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Adjustments to acquisition related contingent consideration liability			$ 11
Increase in fair value of contingent consideration due to 5% increase in projections			22
Decrease in fair value of contingent consideration due to 5% decrease in projections			(23)
Carrying value of investment	$ 391		391			$ 405
Unrealized investment gains	0	$ 24	0	$ 19
Other investments	64		$ 64
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	63		$ 63			63
Private Equity Funds, Non-US
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Carrying value of investment	82		82			$ 76
Equity Securities
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investments, fair value	113		113
Alexander Forbes Group Holdings Limited
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) | R / shares					R 5.77		R 7.50
Carrying value of investment	$ 246		$ 246
Percentage of ownership in equity investment	33.00%		33.00%
Investment shares owned | shares	443		443
Market value of investment	$ 188		$ 188
Share price, weighted average (per share amount) | R / shares					R 6.66
Share price, percentage of cost basis	89.00%		89.00%
Alexander Forbes Group Holdings Limited | Minimum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) | $ / shares	$ 5		$ 5
Share price, percentage of purchase price	67.00%		67.00%
Alexander Forbes Group Holdings Limited | Maximum
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) | $ / shares	$ 7.34		$ 7.34
Share price, percentage of purchase price	98.00%		98.00%
Benefitfocus
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unrealized investment gains			$ 19
Money Market Funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Share price (per share amount) | $ / shares	$ 1		$ 1

Fair Value Measurements (Assets

Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) - Fair Value, Measurements, Recurring - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Financial instruments owned:
Total assets measured at fair value		$ 276	$ 382
Fiduciary Assets:
Fiduciary assets		129	111
Liabilities:
Total liabilities measured at fair value		185	189
Identical Assets (Level 1)
Financial instruments owned:
Total assets measured at fair value		276	382
Fiduciary Assets:
Fiduciary assets		129	111
Liabilities:
Total liabilities measured at fair value		0	0
Observable Inputs (Level 2)
Financial instruments owned:
Total assets measured at fair value		0	0
Fiduciary Assets:
Fiduciary assets		0	0
Liabilities:
Total liabilities measured at fair value		0	0
Unobservable Inputs (Level 3)
Financial instruments owned:
Total assets measured at fair value		0	0
Fiduciary Assets:
Fiduciary assets		0	0
Liabilities:
Total liabilities measured at fair value		185	189
Money Market Funds
Fiduciary Assets:
Fiduciary assets		129	111
Money Market Funds | Identical Assets (Level 1)
Fiduciary Assets:
Fiduciary assets		129	111
Money Market Funds | Observable Inputs (Level 2)
Fiduciary Assets:
Fiduciary assets		0	0
Money Market Funds | Unobservable Inputs (Level 3)
Fiduciary Assets:
Fiduciary assets		0	0
Other Assets
Financial instruments owned:
Exchange traded equity securities	[1]	99	81
Mutual funds	[1]	144	158
Other Assets | Identical Assets (Level 1)
Financial instruments owned:
Exchange traded equity securities	[1]	99	81
Mutual funds	[1]	144	158
Other Assets | Observable Inputs (Level 2)
Financial instruments owned:
Exchange traded equity securities	[1]	0	0
Mutual funds	[1]	0	0
Other Assets | Unobservable Inputs (Level 3)
Financial instruments owned:
Exchange traded equity securities	[1]	0	0
Mutual funds	[1]	0	0
Cash and Cash Equivalents
Financial instruments owned:
Money market funds	[2]	33	143
Cash and Cash Equivalents | Identical Assets (Level 1)
Financial instruments owned:
Money market funds	[2]	33	143
Cash and Cash Equivalents | Observable Inputs (Level 2)
Financial instruments owned:
Money market funds	[2]	0	0
Cash and Cash Equivalents | Unobservable Inputs (Level 3)
Financial instruments owned:
Money market funds	[2]	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities
Liabilities:
Contingent purchase consideration liability	[3]	185	189
Accounts Payable and Accrued Liabilities and Other Liabilities | Identical Assets (Level 1)
Liabilities:
Contingent purchase consideration liability	[3]	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Observable Inputs (Level 2)
Liabilities:
Contingent purchase consideration liability	[3]	0	0
Accounts Payable and Accrued Liabilities and Other Liabilities | Unobservable Inputs (Level 3)
Liabilities:
Contingent purchase consideration liability	[3]	$ 185	$ 189
[1]	Included in other assets in the consolidated balance sheets.
[2]	Included in cash and cash equivalents in the consolidated balance sheets.
[3]	Included in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.

Fair Value Measurements (Change

Fair Value Measurements (Changes In Fair Value Of Level 3 Liabilities Representing Acquisition Related Contingent Consideration) (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Revaluation Impact				$ 11	$ (8)
Contingent Consideration
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period,		$ 161	$ 247	189	241
Additions		20	0	26	34
Payments		(1)	(53)	(41)	(65)
Revaluation Impact		6	8		(8)
Other	[1]	(1)	1	0	1
Balance at June 30,		$ 185	$ 203	$ 185	$ 203
[1]	Primarily reflects the impact of foreign exchange.

Retirement Benefits (Narrative)

Retirement Benefits (Narrative) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer	$ 55
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Estimated future employer contributions in current fiscal year	54
United States
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 67	$ 65
United States | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	64.00%
Actual asset allocation percentage of equity	63.00%
United States | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	36.00%
Actual asset allocation percentage of equity	37.00%
United Kingdom
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan, cost recognized	$ 42	$ 38
United Kingdom | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	34.00%
Actual asset allocation percentage of equity	35.00%
United Kingdom | Fixed Income Funds
Defined Benefit Plan Disclosure [Line Items]
Target asset allocation, percentage	66.00%
Actual asset allocation percentage of equity	65.00%
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) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Defined Benefit Plan Disclosure [Line Items]
Compensation and benefits expense (Operating income)	$ (691)	$ (701)	$ (1,599)	$ (1,450)
Other net benefit credits	(65)	(63)	(131)	(123)
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	19	17	37
Interest cost	117	124	235	246
Expected return on plan assets	(218)	(230)	(439)	(454)
Amortization of prior service cost	(1)	(1)	(1)	(1)
Recognized actuarial loss	37	43	74	83
Net periodic benefit (credit) cost	(58)	(45)	(114)	(89)
Curtailment loss (credit)			0	(1)
Settlement loss			0	1
Compensation and benefits expense (Operating income)	(7)	(19)	(17)	(37)
Other net benefit credits	(65)	(64)	(131)	(126)
Total (credit) cost	(58)	(45)	(114)	(89)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	2	2
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(1)	0	(2)	1
Recognized actuarial loss	0	0	0	0
Net periodic benefit (credit) cost	0	1	0	3
Curtailment loss (credit)			0	0
Settlement loss			0	0
Compensation and benefits expense (Operating income)	0	0	0	0
Other net benefit credits	0	1	0	3
Total (credit) cost	0	1	0	3
Domestic Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	59	66	118	132
Expected return on plan assets	(90)	(90)	(179)	(179)
Amortization of prior service cost	0	0	0	0
Recognized actuarial loss	14	10	27	19
Net periodic benefit (credit) cost	(17)	(14)	(34)	(28)
Domestic Plan | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	1	1	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	(1)	1	(1)	2
Recognized actuarial loss	0	(1)	0	(1)
Net periodic benefit (credit) cost	0	1	0	2
Foreign Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	7	19	17	37
Interest cost	58	58	117	114
Expected return on plan assets	(128)	(140)	(260)	(275)
Amortization of prior service cost	(1)	(1)	(1)	(1)
Recognized actuarial loss	23	33	47	64
Net periodic benefit (credit) cost	(41)	(31)	(80)	(61)
Curtailment loss (credit)			0	(1)
Settlement loss			0	1
Total (credit) cost			(80)	(61)
Foreign Plan | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	0	0
Interest cost	0	0	1	1
Expected return on plan assets	0	0	0	0
Amortization of prior service cost	0	(1)	(1)	(1)
Recognized actuarial loss	0	1	0	1
Net periodic benefit (credit) cost	$ 0	$ 0	0	1
Curtailment loss (credit)			0	0
Settlement loss			0	0
Total (credit) cost			$ 0	$ 1

Retirement Benefits (Schedule64

Retirement Benefits (Schedule Of Defined Benefit Plan Weighted Average Assumption Used In Calculating Net Periodic Benefit Cost) (Details)	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Pension Benefits
Weighted average assumptions:
Expected return on plan assets	5.83%	6.64%
Discount rate	3.07%	3.40%
Rate of compensation increase	1.73%	1.77%
Postretirement Benefits
Weighted average assumptions:
Expected return on plan assets	0.00%	0.00%
Discount rate	3.21%	3.64%
Rate of compensation increase	0.00%	0.00%

Debt (Schedule Of Outstanding D

Debt (Schedule Of Outstanding Debt) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jan. 31, 2017
Debt Instrument [Line Items]
Commercial paper outstanding	$ 175	$ 0
Current portion of long-term debt	264	262
Short-term debt	439	262
Long-term debt, current and noncurrent	6,077	5,487
Long-term debt	5,813	5,225
2.55% Senior Debt Obligations Due 2018
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 250	250
Interest rate	2.55%
2.35% Senior Debt Obligations Due 2019
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 299	299
Interest rate	2.35%
2.35% Senior Debt Obligations Due 2020
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 499	498
Interest rate	2.35%
4.80% Senior Debt Obligations Due 2021
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 498	498
Interest rate	4.80%
2.75% Senior Debt Obligations Due 2022
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 497	496
Interest rate	2.75%		2.75%
3.30% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 348	348
Interest rate	3.30%
4.05% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 248	248
Interest rate	4.05%
3.50% Senior Debt Obligations Due 2024
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 597	596
Interest rate	3.50%
3.50% Senior Debt Obligations Due 2025
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 496	496
Interest rate	3.50%
3.75% Senior Debt Obligations Due 2026
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 596	596
Interest rate	3.75%
5.875% Senior Debt Obligations Due 2033
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 297	297
Interest rate	5.875%
4.35% Senior Debt Obligation Due 2047
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 492	492
Interest rate	4.35%		4.35%
4.20% Senior Debt Obligations Due 2048
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 592	0
Interest rate	4.20%
Mortgage Due 2035
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 364	370
Interest rate	5.70%
Other
Debt Instrument [Line Items]
Long-term debt, current and noncurrent	$ 4	$ 3

Debt (Narrative) (Details)

Debt (Narrative) (Details) - USD ($)	1 Months Ended	6 Months Ended
	Apr. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jan. 31, 2017
Debt Instrument [Line Items]
Commercial paper outstanding		$ 175,000,000	$ 0
Repayments of senior debt	$ 250,000,000
4.20% Senior Debt Obligations Due 2048
Debt Instrument [Line Items]
Proceeds from issuance of debt		$ 600,000,000
Interest rate		4.20%
2.75% Senior Debt Obligations Due 2022
Debt Instrument [Line Items]
Proceeds from issuance of debt				$ 500,000,000
Interest rate		2.75%		2.75%
4.35% Senior Debt Obligation Due 2047
Debt Instrument [Line Items]
Proceeds from issuance of debt				$ 500,000,000
Interest rate		4.35%		4.35%
3.30% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Interest rate		3.30%
Amended Revolving Credit Facility March 27, 2014
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity		$ 1,500,000,000
Term of debt		5 years
Revolving credit facility, amount outstanding		$ 0
Commercial Paper
Debt Instrument [Line Items]
Debt financing program		$ 1,500,000,000
Effective interest rate		2.25%

Debt (Estimated Fair Value of S

Debt (Estimated Fair Value of Significant Financial Instruments) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Carrying Amount
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	$ 439	$ 262
Long-term debt	5,813	5,225
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Short-term debt	440	264
Long-term debt	$ 5,826	$ 5,444

Restructuring Costs (Restructur

Restructuring Costs (Restructuring Activities) (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended	12 Months Ended
	Jun. 30, 2016	Jun. 30, 2018	Dec. 31, 2017
Restructuring Reserve [Roll Forward]
Liability at beginning of period		$ 65	$ 93
Amounts Accrued		64	40
Cash Paid		(41)	(71)
Other		(1)	3
Liability at end of period		87	65
Severance and Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Amounts Accrued		9
Severance
Restructuring Cost and Reserve [Line Items]
Restructuring costs	$ 55
Restructuring Reserve [Roll Forward]
Liability at beginning of period		15	32
Amounts Accrued		51	31
Cash Paid		(22)	(49)
Other		(1)	1
Liability at end of period		43	15
Future rent under non-cancelable leases and other costs
Restructuring Reserve [Roll Forward]
Liability at beginning of period		50	61
Amounts Accrued		13	9
Cash Paid		(19)	(22)
Other		0	2
Liability at end of period		44	$ 50
Operating Segments | Risk and Insurance Services Segment | Acquisition Related
Restructuring Reserve [Roll Forward]
Amounts Accrued		3
Operating Segments | Consulting Segment | Acquisition Related
Restructuring Reserve [Roll Forward]
Amounts Accrued		1
Corporate | Acquisition Related
Restructuring Reserve [Roll Forward]
Amounts Accrued		$ 5

Common Stock (Details)

Common Stock (Details) - USD ($) shares in Millions, $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Nov. 30, 2016
Equity, Class of Treasury Stock [Line Items]
Payments for repurchase of common stock	$ 500	$ 400
Stock-based compensation, shares issued during period	2.5	3.7
Common Stock
Equity, Class of Treasury Stock [Line Items]
Common stock repurchased (in shares)	6.1	5.4
Payments for repurchase of common stock	$ 500	$ 400
Share repurchases program, authorized amount (up to)			$ 2,500
Stock repurchase program, remaining authorized repurchase amount	$ 1,000

Claims, Lawsuits And Other Co70

Claims, Lawsuits And Other Contingencies (Details) £ in Millions	Jun. 30, 2018GBP (£)
Other Contingencies-Guarantees
Loss Contingencies [Line Items]
Amount reinsured by third party (up to)	£ 40

Segment Information (Selected I

Segment Information (Selected Information And Details For MMC's Operating Segments) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue	$ 3,734	$ 3,495	$ 7,734	$ 6,998
Operating Income (Loss)	691	701	1,599	1,450
Equity method income	2		9
Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Interest on fiduciary funds (less than)	15		28
Operating Segments
Segment Reporting Information [Line Items]
Revenue	3,746	3,508	7,758	7,023
Operating Income (Loss)	739	747	1,702	1,540
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,096	1,916	4,440	3,905
Operating Income (Loss)	472	482	1,188	1,050
Interest on fiduciary funds (less than)	15	9	28	17
Equity method income	7	7	6	9
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,650	1,592	3,318	3,118
Operating Income (Loss)	267	265	514	490
Interest on fiduciary funds (less than)	1	1	2	1
Equity method income	5	5	8	9
Corporate and Eliminations
Segment Reporting Information [Line Items]
Revenue	(12)	(13)	(24)	(25)
Operating Income (Loss)	(48)	(46)	(103)	(90)
Intersegment Eliminations | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue		4	1	4
Intersegment Eliminations | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	$ 12	$ 9	$ 23	$ 21

Segment Information (Details of

Segment Information (Details of Operating Segment Revenue) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Revenue	$ 3,734	$ 3,495	$ 7,734	$ 6,998
Operating Segments
Segment Reporting Information [Line Items]
Revenue	3,746	3,508	7,758	7,023
Operating Segments | Risk and Insurance Services Segment
Segment Reporting Information [Line Items]
Revenue	2,096	1,916	4,440	3,905
Operating Segments | Risk and Insurance Services Segment | Marsh Insurance Group
Segment Reporting Information [Line Items]
Revenue	1,760	1,621	3,463	3,223
Operating Segments | Risk and Insurance Services Segment | Guy Carpenter Reinsurance Group
Segment Reporting Information [Line Items]
Revenue	336	295	977	682
Operating Segments | Consulting Segment
Segment Reporting Information [Line Items]
Revenue	1,650	1,592	3,318	3,118
Operating Segments | Consulting Segment | Mercer Consulting Group
Segment Reporting Information [Line Items]
Revenue	1,158	1,109	2,329	2,186
Operating Segments | Consulting Segment | Oliver Wyman Group Consulting Group
Segment Reporting Information [Line Items]
Revenue	492	483	989	932
Corporate and Eliminations
Segment Reporting Information [Line Items]
Revenue	$ (12)	$ (13)	$ (24)	$ (25)

New Accounting Guidance - Narra

New Accounting Guidance - Narrative (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 14,131	$ 13,504	$ 13,140
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		14	$ 14
Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings	$ 364	364
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings		(14)
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)

New Accounting Guidance - ASC 6

New Accounting Guidance - ASC 606 (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues [Abstract]
Revenue	$ 3,734	$ 3,495	$ 7,734	$ 6,998
Expense:
Compensation and benefits	2,135	1,998	4,359	4,003
Other operating expenses	908	796	1,776	1,545
Operating expenses	3,043	2,794	6,135	5,548
Operating income	691	701	1,599	1,450
Other net benefit credits	65	63	131	123
Interest income	3	2	6	4
Interest expense	(68)	(60)	(129)	(118)
Investment Income	28	5	28	5
Income before income taxes	719	711	1,635	1,464
Income tax expense	183	204	403	379
Net income before non-controlling interests	536	507	1,232	1,085
Less: Net income attributable to non-controlling interests	5	6	11	15
Net income attributable to the Company	531	501	1,221	1,070
Assets
Cash and cash equivalents	1,036	966	1,036	966		$ 1,205	$ 1,026
Net receivables	4,601		4,601		$ 4,201	4,133
Other current assets	538		538		542	224
Total current assets	6,175		6,175			5,562
Fixed assets, net	698		698			712
Pension related assets	1,808		1,808			1,693
Deferred tax assets	532		532		552	669
Total assets	21,159		21,159			20,429
Liabilities
Short-term debt	439		439			262
Accounts payable and accrued liabilities	2,246		2,246		2,205	2,083
Accrued compensation and employee benefits	1,103		1,103			1,718
Accrued income taxes	216		216			199
Dividends payable	212		212			0
Total current liabilities	4,216		4,216			4,262
Fiduciary liabilities	5,118		5,118			4,847
Less – cash and investments held in a fiduciary capacity	(5,118)		(5,118)			(4,847)
Fiduciary Liabilities, Net, Noncurrent	0		0			0
Long-term debt	5,813		5,813			5,225
Pension, post-retirement and post-employment benefits	1,768		1,768			1,888
Liabilities for errors and omissions	303		303			301
Other liabilities	1,262		1,262		1,334	1,311
Equity [Abstract]
Retained earnings	14,131		14,131		13,504	13,140
Total equity	7,797	7,074	7,797	7,074		7,442
Total liabilities and stockholders' equity	21,159		21,159			$ 20,429
Statement of Cash Flows [Abstract]
Net income before non-controlling interests	536	$ 507	1,232	1,085
Depreciation and amortization of fixed assets and capitalized software			159	156
Amortization of intangible assets			88	80
Adjustments and payments related to contingent consideration liability			2	(13)
Provision for deferred income taxes			34	42
(Gain) loss on investments			(28)	(5)
(Gain) loss on disposition of assets			(1)	9
Share-based compensation expense			99	75
Net receivables			(388)	(318)
Other current assets			4	(18)
Other assets			(10)	(34)
Accounts payable and accrued liabilities			30	52
Accrued compensation and employee benefits			(614)	(579)
Accrued income taxes			18	45
Contributions to pension and other benefit plans in excess of current year expense/credit			(178)	(214)
Other liabilities			(10)	9
Effect of exchange rate changes			(24)	(29)
Net cash provided by operations			413	$ 343
Accounting Standards Update 2014-09
Revenues [Abstract]
Revenue	3,734		7,734
Expense:
Compensation and benefits	2,135		4,359
Other operating expenses	908		1,776
Operating expenses	3,043		6,135
Operating income	691		1,599
Other net benefit credits	65		131
Interest income	3		6
Interest expense	(68)		(129)
Investment Income	28		28
Income before income taxes	719		1,635
Income tax expense	183		403
Net income before non-controlling interests	536		1,232
Less: Net income attributable to non-controlling interests	5		11
Net income attributable to the Company	531		1,221
Assets
Cash and cash equivalents	1,036		1,036
Net receivables	4,601		4,601		68
Other current assets	538		538		318
Total current assets	6,175		6,175
Goodwill and intangible assets	10,411		10,411
Fixed assets, net	698		698
Pension related assets	1,808		1,808
Deferred tax assets	532		532		(103)
Other assets	1,535		1,535
Total assets	21,159		21,159
Liabilities
Short-term debt	439		439
Accounts payable and accrued liabilities	2,246		2,246		122
Accrued compensation and employee benefits	1,103		1,103
Accrued income taxes	216		216
Dividends payable	212		212
Total current liabilities	4,216		4,216
Fiduciary liabilities	5,118		5,118
Less – cash and investments held in a fiduciary capacity	(5,118)		(5,118)
Fiduciary Liabilities, Net, Noncurrent	0		0
Long-term debt	5,813		5,813
Pension, post-retirement and post-employment benefits	1,768		1,768
Liabilities for errors and omissions	303		303
Other liabilities	1,262		1,262		23
Equity [Abstract]
Retained earnings	364		364		$ 364
Total equity	7,797		7,797
Total liabilities and stockholders' equity	21,159		21,159
Statement of Cash Flows [Abstract]
Net income before non-controlling interests			1,232
Depreciation and amortization of fixed assets and capitalized software			159
Amortization of intangible assets			88
Adjustments and payments related to contingent consideration liability			2
Provision for deferred income taxes			34
(Gain) loss on investments			(28)
(Gain) loss on disposition of assets			(1)
Share-based compensation expense			99
Net receivables			(388)
Other current assets			4
Other assets			(10)
Accounts payable and accrued liabilities			30
Accrued compensation and employee benefits			(614)
Accrued income taxes			18
Contributions to pension and other benefit plans in excess of current year expense/credit			(178)
Other liabilities			(10)
Effect of exchange rate changes			(24)
Net cash provided by operations			413
Calculated under Revenue Guidance in Effect before Topic 606 | Accounting Standards Update 2014-09
Revenues [Abstract]
Revenue	3,710		7,549
Expense:
Compensation and benefits	2,125		4,289
Other operating expenses	908		1,776
Operating expenses	3,033		6,065
Operating income	677		1,484
Other net benefit credits	65		131
Interest income	3		6
Interest expense	(68)		(129)
Investment Income	28		28
Income before income taxes	705		1,520
Income tax expense	179		373
Net income before non-controlling interests	526		1,147
Less: Net income attributable to non-controlling interests	5		11
Net income attributable to the Company	521		1,136
Assets
Cash and cash equivalents	1,036		1,036
Net receivables	4,347		4,347
Other current assets	240		240
Total current assets	5,623		5,623
Goodwill and intangible assets	10,411		10,411
Fixed assets, net	698		698
Pension related assets	1,808		1,808
Deferred tax assets	665		665
Other assets	1,305		1,305
Total assets	20,510		20,510
Liabilities
Short-term debt	439		439
Accounts payable and accrued liabilities	2,069		2,069
Accrued compensation and employee benefits	1,103		1,103
Accrued income taxes	216		216
Dividends payable	212		212
Total current liabilities	4,039		4,039
Fiduciary liabilities	5,118		5,118
Less – cash and investments held in a fiduciary capacity	(5,118)		(5,118)
Fiduciary Liabilities, Net, Noncurrent	0		0
Long-term debt	5,813		5,813
Pension, post-retirement and post-employment benefits	1,768		1,768
Liabilities for errors and omissions	303		303
Other liabilities	1,239		1,239
Equity [Abstract]
Total equity	7,348		7,348
Total liabilities and stockholders' equity	20,510		20,510
Statement of Cash Flows [Abstract]
Net income before non-controlling interests			1,147
Depreciation and amortization of fixed assets and capitalized software			159
Amortization of intangible assets			88
Adjustments and payments related to contingent consideration liability			2
Provision for deferred income taxes			34
(Gain) loss on investments			(28)
(Gain) loss on disposition of assets			(1)
Share-based compensation expense			99
Net receivables			(202)
Other current assets			(16)
Other assets			(36)
Accounts payable and accrued liabilities			(25)
Accrued compensation and employee benefits			(614)
Accrued income taxes			18
Contributions to pension and other benefit plans in excess of current year expense/credit			(178)
Other liabilities			(10)
Effect of exchange rate changes			(24)
Net cash provided by operations			413
Difference between Revenue Guidance in Effect before and after Topic 606 | Accounting Standards Update 2014-09
Revenues [Abstract]
Revenue	(24)		(185)
Expense:
Compensation and benefits	(10)		(70)
Other operating expenses	0		0
Operating expenses	(10)		(70)
Operating income	(14)		(115)
Other net benefit credits	0		0
Interest income	0		0
Interest expense	0		0
Investment Income	0		0
Income before income taxes	(14)		(115)
Income tax expense	(4)		(30)
Net income before non-controlling interests	(10)		(85)
Less: Net income attributable to non-controlling interests	0		0
Net income attributable to the Company	(10)		(85)
Assets
Cash and cash equivalents	0		0
Net receivables	(254)		(254)
Other current assets	(298)		(298)
Total current assets	(552)		(552)
Goodwill and intangible assets	0		0
Fixed assets, net	0		0
Pension related assets	0		0
Deferred tax assets	133		133
Other assets	(230)		(230)
Total assets	(649)		(649)
Liabilities
Short-term debt	0		0
Accounts payable and accrued liabilities	(177)		(177)
Accrued compensation and employee benefits	0		0
Accrued income taxes	0		0
Dividends payable	0		0
Total current liabilities	(177)		(177)
Fiduciary liabilities	0		0
Less – cash and investments held in a fiduciary capacity	0		0
Fiduciary Liabilities, Net, Noncurrent	0		0
Long-term debt	0		0
Pension, post-retirement and post-employment benefits	0		0
Liabilities for errors and omissions	0		0
Other liabilities	(23)		(23)
Equity [Abstract]
Total equity	(449)		(449)
Total liabilities and stockholders' equity	$ (649)		(649)
Statement of Cash Flows [Abstract]
Net income before non-controlling interests			(85)
Depreciation and amortization of fixed assets and capitalized software			0
Amortization of intangible assets			0
Adjustments and payments related to contingent consideration liability			0
Provision for deferred income taxes			0
(Gain) loss on investments			0
(Gain) loss on disposition of assets			0
Share-based compensation expense			0
Net receivables			186
Other current assets			(20)
Other assets			(26)
Accounts payable and accrued liabilities			(55)
Accrued compensation and employee benefits			0
Accrued income taxes			0
Contributions to pension and other benefit plans in excess of current year expense/credit			0
Other liabilities			0
Effect of exchange rate changes			0
Net cash provided by operations			$ 0

New Accounting Guidance - Early

New Accounting Guidance - Early Adoption (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Disaggregation of Revenue [Line Items]
Net receivables	$ 4,601	$ 4,201	$ 4,133
Other current assets	538	542	224
Other assets	1,535	1,656	1,430
Deferred tax assets	532	552	669
Accounts payable and accrued liabilities	2,246	2,205	2,083
Other liabilities	1,262	1,334	1,311
Other Accumulated Comprehensive Income		(14)	0
Retained earnings	14,131	13,504	$ 13,140
Accounting Standards Update 2014-09
Disaggregation of Revenue [Line Items]
Net receivables	4,601	68
Other current assets	538	318
Other assets		226
Deferred tax assets	532	(103)
Accounts payable and accrued liabilities	2,246	122
Other liabilities	1,262	23
Other Accumulated Comprehensive Income		0
Retained earnings	$ 364	364
Accounting Standards Update 2016-01
Disaggregation of Revenue [Line Items]
Net receivables		0
Other current assets		0
Other assets		0
Deferred tax assets		0
Accounts payable and accrued liabilities		0
Other liabilities		0
Other Accumulated Comprehensive Income		(14)
Retained earnings		14
Accounting Standards Update 2016-16
Disaggregation of Revenue [Line Items]
Net receivables		0
Other current assets		0
Other assets		0
Deferred tax assets		(14)
Accounts payable and accrued liabilities		0
Other liabilities		0
Other Accumulated Comprehensive Income		0
Retained earnings		$ (14)