Marsh & McLennan Companies (MMC) 10-Q 8 May 14 2014 Q1 Quarterly report Financial data

Document_and_Entity_Informatio

Document and Entity Information	3 Months Ended
	Mar. 31, 2014	Apr. 30, 2014
Document And Entity Information [Abstract]	'	'
Entity Registrant Name	'MARSH & MCLENNAN COMPANIES, INC.	'
Entity Central Index Key	'0000062709	'
Trading Symbol	'MMC	'
Current Fiscal Year End Date	'--12-31	'
Entity Filer Category	'Large Accelerated Filer	'
Document Type	'10-Q	'
Document Period End Date	31-Mar-14	'
Document Fiscal Year Focus	'2014	'
Document Fiscal Period Focus	'Q1	'
Amendment Flag	'false	'
Entity Common Stock, Shares Outstanding	'	549,601,256

Consolidated_Statements_of_Inc

Consolidated Statements of Income (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Revenue	$3,264	$3,126
Expense:	'	'
Compensation and benefits	1,839	1,803
Other operating expenses	752	716
Operating expenses	2,591	2,519
Operating income	673	607
Interest income	5	4
Interest expense	-42	-44
Investment income	13	21
Income before income taxes	649	588
Income tax expense	192	176
Income from continuing operations	457	412
Discontinued operations, net of tax	-1	12
Net income before non-controlling interests	456	424
Less: Net income attributable to non-controlling interests	13	11
Net income attributable to the Company	$443	$413
Basic net income per share	'	'
- Continuing operations	$0.81	$0.73
– Net income attributable to the Company	$0.81	$0.75
Diluted net income per share	'	'
- Continuing operations	$0.80	$0.72
– Net income attributable to the Company	$0.80	$0.74
Average number of shares outstanding	'	'
- Basic (in shares)	548	548
- Diluted (in shares)	556	557
Shares outstanding at March 31	549	550

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Net income before non-controlling interests	$456	$424
Other comprehensive income (loss), before tax:	'	'
Foreign currency translation adjustments	71	-260
Unrealized investment loss	0	0
Gain (loss) related to pension/post-retirement plans	-199	252
Other comprehensive loss, before tax	-128	-8
Income tax expense (benefit) on other comprehensive income	-41	64
Other comprehensive loss, net of tax	-87	-72
Comprehensive income	369	352
Less: comprehensive income attributable to non-controlling interest	13	11
Comprehensive income attributable to the Company	$356	$341

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$1,380	$2,303
Receivables	'	'
Commissions and fees	3,209	3,065
Advanced premiums and claims	55	61
Other	300	282
Gross receivables	3,564	3,408
Less-allowance for doubtful accounts and cancellations	-102	-98
Net receivables	3,462	3,310
Current deferred tax assets	484	482
Other current assets	237	205
Total current assets	5,563	6,300
Goodwill and intangible assets	7,799	7,365
Fixed assets (net of accumulated depreciation and amortization of $1,616 at March 31, 2014 and $1,597 at December 31, 2013)	825	828
Pension related assets	889	979
Deferred tax assets	564	626
Other assets	937	882
Total assets	16,577	16,980
Current liabilities:	'	'
Short-term debt	432	334
Accounts payable and accrued liabilities	1,895	1,861
Accrued compensation and employee benefits	701	1,466
Accrued income taxes	176	148
Dividends payable	139	'
Total current liabilities	3,343	3,809
Fiduciary liabilities	4,814	4,234
Less – cash and investments held in a fiduciary capacity	-4,814	-4,234
Net fiduciary assets	0	0
Long-term debt	2,619	2,621
Pension, post-retirement and post-employment benefits	1,135	1,150
Liabilities for errors and omissions	354	373
Other liabilities	1,083	1,052
Commitments and contingencies	'	'
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 March 31, 2014 and December 31, 2013	561	561
Additional paid-in capital	909	1,028
Retained earnings	9,620	9,452
Accumulated other comprehensive loss	-2,708	-2,621
Non-controlling interests	82	70
Stockholders' equity before treasury stock	8,464	8,490
Less – treasury shares, at cost, 11,358,687 shares at March 31, 2014 and 13,882,204 shares at December 31, 2013	-421	-515
Total equity	8,043	7,975
Total liabilities and stockholders' equity	$16,577	$16,980

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, except Share data, unless otherwise specified
Statement of Financial Position [Abstract]	'	'
Fixed assets, accumulated depreciation and amortization	$1,616	$1,597
Preferred stock, par value	$1	$1
Preferred stock, shares authorized	6,000,000	6,000,000
Preferred stock, shares issued	0	0
Common stock, par value	$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	11,358,687	13,882,204

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Operating cash flows:	'	'
Net income before non-controlling interests	$456	$424
Adjustments to reconcile net income to cash provided by operations:	'	'
Depreciation and amortization of fixed assets and capitalized software	75	69
Amortization of intangible assets	22	18
Adjustments to acquisition related contingent consideration liability	-6	1
Provision for deferred income taxes	59	51
Gain on investments	-13	-21
Loss on disposition of assets	1	2
Share based compensation expense	33	42
Changes in assets and liabilities:	'	'
Net receivables	-150	-120
Other current assets	-35	-54
Other assets	33	-14
Accounts payable and accrued liabilities	47	53
Accrued compensation and employee benefits	-764	-727
Accrued income taxes	28	39
Contributions to pension and other benefit plans in excess of current year expense/credit	-93	-350
Other liabilities	-85	-42
Effect of exchange rate changes	12	36
Net cash used for operations	-380	-593
Financing cash flows:	'	'
Purchase of treasury shares	-100	-100
Net increase in commercial paper	100	0
Proceeds from debt	0	50
Repayments of debt	-3	-252
Shares withheld for taxes on vested units – treasury shares	-49	-65
Issuance of common stock from treasury shares	92	135
Payments of contingent consideration for acquisitions	-20	-3
Distributions of non-controlling interests	-1	-2
Dividends paid	-137	-127
Net cash used for financing activities	-118	-364
Investing cash flows:	'	'
Capital expenditures	-99	-88
Net sales of long-term investments	0	92
Proceeds from sales of fixed assets	1	1
Dispositions	0	3
Acquisitions	-319	-1
Other, net	1	1
Net cash (used for) provided by investing activities	-416	8
Effect of exchange rate changes on cash and cash equivalents	-9	-89
Decrease in cash and cash equivalents	-923	-1,038
Cash and cash equivalents at beginning of period	2,303	2,301
Cash and cash equivalents at end of period	$1,380	$1,263

Consolidated_Statements_of_Equ

Consolidated Statements of Equity (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	Treasury Shares [Member]	Non-Controlling Interests [Member]
In Millions, unless otherwise specified
Balance, beginning of year at Dec. 31, 2012	'	$561	$1,107	$8,628	($3,307)	($447)	$64
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'
Change in accrued stock compensation costs	'	'	-89	'	'	'	'
Issuance of shares under stock compensation plans and employee stock purchase plans and related tax impact	'	'	-25	'	'	226	'
Net income	424	'	'	413	'	'	11
Dividend equivalents declared - (per share amounts: $0.50 in 2014 and $0.46 in 2013)	'	'	'	-3	'	'	'
Dividends declared – (per share amounts: $0.50 in 2014 and $0.46 in 2013)	'	'	'	-252	'	'	'
Other comprehensive loss, net of tax	-72	'	'	'	-72	'	'
Purchase of treasury shares	'	'	'	'	'	-100	'
Other changes	'	'	'	'	'	'	-2
Balance, end of period at Mar. 31, 2013	6,713	561	993	8,786	-3,379	-321	73
Balance, beginning of year at Dec. 31, 2013	7,975	561	1,028	9,452	-2,621	-515	70
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'
Change in accrued stock compensation costs	'	'	-59	'	'	'	'
Issuance of shares under stock compensation plans and employee stock purchase plans and related tax impact	'	'	-60	'	'	194	'
Net income	456	'	'	443	'	'	13
Dividend equivalents declared - (per share amounts: $0.50 in 2014 and $0.46 in 2013)	'	'	'	-1	'	'	'
Dividends declared – (per share amounts: $0.50 in 2014 and $0.46 in 2013)	'	'	'	-274	'	'	'
Other comprehensive loss, net of tax	-87	'	'	'	-87	'	'
Purchase of treasury shares	'	'	'	'	'	-100	'
Other changes	'	'	'	'	'	'	-1
Balance, end of period at Mar. 31, 2014	$8,043	$561	$909	$9,620	($2,708)	($421)	$82

Consolidated_Statements_of_Equ1

Consolidated Statements of Equity (Parenthetical) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Statement of Stockholders' Equity [Abstract]	'	'
Dividends declared per share (in dollars per share)	$0.50	$0.46
Dividend equivalents declared per share (in dollars per share)	$0.50	$0.46

Nature_of_Operations

Nature of Operations	3 Months Ended
	Mar. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Nature of Operations	'
	Nature of Operations
	Marsh & McLennan Companies, Inc. (“the Company”), a global professional services firm, is organized based on the different services that it offers. Under this organizational structure, the Company’s two business segments are Risk and Insurance Services and Consulting.
	The Risk and Insurance Services segment provides risk management activities 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 two main business groups. Mercer provides consulting expertise, advice, services and solutions in the areas of health, retirement, talent and investments. 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 7 to the consolidated financial statements.

Principles_of_Consolidation_an

Principles of Consolidation and Other Matters	3 Months Ended
	Mar. 31, 2014
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, 2013 (the “2013 10-K”).
	The financial information contained herein reflects all adjustments consisting only of 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-month periods ended March 31, 2014 and 2013.
	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 $190 million related to regulatory requirements outside the U.S. or as collateral under captive insurance arrangements.
	Investment Income
	The caption “Investment income” in the consolidated statements of income comprises realized and unrealized gains and losses from investments recognized in current earnings. It includes, when applicable, other than temporary declines in the value of debt and available for sale securities and the change in value of the Company’s holdings in certain private equity funds, including equity method gains (losses) on its investment in the Trident funds. The Company’s investments may include direct investments in insurance or consulting companies and investments in private equity funds. Trident II fully harvested all its portfolio investments and made final distributions to its partners during the fourth quarter of 2013. As of the end of 2013, the Company recognized all the performance fees related to its general partnership interest in Trident II. The Company recorded gains on its investment in Trident II of $20 million, including $15 million of deferred performance fees, for the three months ended March 31, 2013. Investment income for the three months ended March 31, 2014 includes performance fees of $7 million from Trident III which had been deferred, and that are no longer subject to claw-back, and also includes approximately $6 million of mark-to-market gains in the Company's private equity investments. At March 31, 2014, the Company had deferred performance fees of approximately $35 million related to Trident III. Recognition of these deferred performance fees will only occur as investments are harvested and the performance fees are no longer subject to claw-back. Timing of this is unknown and is not controlled by the Company.
	Income Taxes
	The Company's effective tax rate in the first quarter of 2014 was 29.5%. The rate reflects the impact of non-U.S. earnings subject to tax at rates below the U.S. statutory rate, including the effect of repatriation. The effective tax rate for the first quarter of 2013 was 29.9%.
	The Company is routinely examined by tax authorities in the jurisdictions in which it has significant operations. The Company regularly considers the likelihood of assessments in each of the taxing jurisdictions resulting from examinations. When evaluating the potential imposition of penalties, the Company considers a number of relevant factors under penalty statutes, including appropriate disclosure of the tax return position, the existence of legal authority supporting the Company's position, and reliance on the opinion of professional tax advisors.
	The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in tax returns. The Company's gross unrecognized tax benefits decreased from
	$128 million at December 31, 2013 to $117 million at March 31, 2014. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $27 million within the next twelve months due to settlement of audits and expiration of statutes of limitation.
	Reclassifications
	In the first quarter of 2014, the Company enhanced its operating cash flow presentation within the statement of cash flows to show on single lines the impact of pension and other benefit plan contributions in excess of the related expenses, and the non-cash impact of equity share awards. Previously, the cash flow impact of those items was presented as part of changes in other assets and other liabilities, and changes in other liabilities, respectively. The prior year’s presentation was conformed to the current presentation for the following line items within operating cash flows:
	•	Share based compensation expense
	•	Changes in other assets
	•	Contributions to pension and other benefit plans in excess of current year expense/credit
	•	Changes in other liabilities

Fiduciary_Assets_and_Liabiliti

Fiduciary Assets and Liabilities	3 Months Ended
	Mar. 31, 2014
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 $6 million and $8 million for the three-month periods ended March 31, 2014 and 2013, respectively. The Consulting segment recorded fiduciary interest income of $1 million in each of the the three-month periods ended March 31, 2014 and 2013. 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 $8.7 billion at March 31, 2014 and $8.2 billion at December 31, 2013. 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. Net uncollected premiums and claims and the related payables are, therefore, 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.
	Mercer manages approximately $17 billion of assets in trusts or funds for which Mercer’s management or trustee fee is considered a variable interest. Mercer is not the primary beneficiary of these trusts or funds. Mercer’s only variable interest in any of these trusts or funds is its unpaid fees, if any. Mercer’s maximum exposure to loss of its interests is, therefore, limited to collection of its fees.

Per_Share_Data

Per Share Data	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Per Share Data	'
	Per Share Data
	Basic net income per share attributable to the Company and income from continuing operations per share are calculated by dividing the respective after-tax income by the weighted average number of outstanding shares of the Company’s common stock.
	Diluted net income per share attributable to the Company and income from continuing operations per share are calculated by dividing the respective after-tax income 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. Reconciliations of the applicable income components used for diluted EPS - Continuing operations and basic weighted average common shares outstanding to diluted weighted average common shares outstanding are presented below. The reconciling items related to the calculation of diluted weighted average common shares outstanding are the same for net income attributable to the Company.
	Basic and Diluted EPS Calculation - Continuing Operations	Three Months Ended
		March 31,
	(In millions, except per share figures)	2014		2013
	Net income from continuing operations	$	457	$	412
	Less: Net income attributable to non-controlling interests	13		11
		$	444	$	401
	Basic weighted average common shares outstanding	548		548
	Dilutive effect of potentially issuable common shares	8		9
	Diluted weighted average common shares outstanding	556		557
	Average stock price used to calculate common stock equivalents	$	47.84	$	36.21
	There were 21.6 million and 28.9 million stock options outstanding as of March 31, 2014 and 2013, respectively.

Supplemental_Disclosures_To_Th

Supplemental Disclosures To The Consolidated Statements Of Cash Flows	3 Months Ended
	Mar. 31, 2014
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 three-month periods ended March 31, 2014 and 2013.
	(In millions of dollars)	2014			2013
	Assets acquired, excluding cash	$	464		$	—
	Liabilities assumed	(38		)	—
	Contingent/deferred purchase consideration	(113		)	—
	Net cash outflow for current year acquisitions	313			—
	Deferred purchase consideration from prior years' acquisitions	6			1
	Net cash outflow for acquisitions	$	319		$	1
	(In millions of dollars)	2014			2013
	Interest paid	$	44		$	59
	Income taxes paid	$	120		$	85
	The Company had non-cash issuances of common stock of $92 million and $130 million, respectively, for the three months ended March 31, 2014 and 2013, primarily related to its share-based payment plans. The Company recorded stock-based compensation expense related to equity awards of $26 million and $34 million for the three-month periods ended March 31, 2014 and 2013, respectively.

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Other Comprehensive Income (Loss)	'
	Other Comprehensive Income (Loss)
	The changes in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the three-month periods ended March 31, 2014 and 2013, including amounts reclassified out of AOCI, are as follows:
	(In millions of dollars)	Unrealized Investment Gains				Pension/Post-Retirement Plans Gains (Losses)				Foreign Currency Translation Adjustments				Total
	Balance as of January 1, 2014	$	5			$	(2,682	)		$	56			$	(2,621	)
	Other comprehensive income (loss) before reclassifications	—				(199		)		78				(121		)
	Amounts reclassified from accumulated other comprehensive income	—				34				—				34
	Net current period other comprehensive income (loss)	—				(165		)		78				(87		)
	Balance as of March 31, 2014	$	5			$	(2,847	)		$	134			$	(2,708	)
	(In millions of dollars)	Unrealized Investment Gains				Pension/Post-Retirement Plans Gains (Losses)				Foreign Currency Translation Adjustments				Total
	Balance as of January 1, 2013	$	4			$	(3,451	)		$	140			$	(3,307	)
	Other comprehensive income (loss) before reclassifications	—				139				(256		)		(117		)
	Amounts reclassified from accumulated other comprehensive income	—				45				—				45
	Net current period other comprehensive income (loss)	—				184				(256		)		(72		)
	Balance as of March 31, 2013	$	4			$	(3,267	)		$	(116	)		$	(3,379	)
	The components of other comprehensive income (loss) for the three-month periods ended March 31, 2014 and 2013 are as follows:
	Three Months Ended March 31,	2014										2013
	(In millions of dollars)	Pre-Tax			Tax			Net of Tax				Pre-Tax			Tax			Net of Tax
	Foreign currency translation adjustments	$	71		$	(7	)	$	78			$	(260	)	$	(4	)	$	(256	)
	Unrealized investment gains (losses)	—			—			—				—			—			—
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains (a)	(3		)	(1		)	(2		)		(6		)	(2		)	(4		)
	Net actuarial losses (a)	51			15			36				78			29			49
	Subtotal	48			14			34				72			27			45
	Effect of remeasurement	(166		)	(33		)	(133		)		—			—			—
	Effect of curtailment	(65		)	(13		)	(52		)		—			—			—
	Foreign currency translation adjustments	(17		)	(2		)	(15		)		180			41			139
	Other	1			—			1				—			—			—
	Pension/post-retirement plans (losses) gains	(199		)	(34		)	(165		)		252			68			184
	Other comprehensive (loss) income	$	(128	)	$	(41	)	$	(87	)		$	(8	)	$	64		$	(72	)
	(a) 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

Acquisitions	3 Months Ended
	Mar. 31, 2014
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	The Company completed six acquisitions during the first three months of 2014.
	In January 2014, Marsh & Mclennan Agency ("MMA") acquired Barney & Barney, a San Diego-based insurance broking firm that provides insurance, risk management, and employee benefits solutions to businesses and individuals throughout the U.S. and abroad. Also in January, Marsh acquired Central Insurance Services, an independent insurance broker in Scotland that provides insurance broking and risk advisory services to companies of all sizes across industry sectors. In February 2014, MMA acquired Great Lakes Employee Benefits Services, Inc., an employee group benefits consulting and brokerage firm based in Michigan, and Bond Network, Inc., a surety bonding agency based in North Carolina. In March 2014, MMA acquired Capstone Insurance Services, LLC, an agency that provides property/casualty insurance and risk management solutions to businesses and individuals throughout South Carolina, and Mercer acquired Transition Assist, a retiree exchange specializing in helping retirees in employer-sponsored plans select Medicare supplemental health care insurance.
	The MMA acquisitions were made to expand Marsh's presence in the U.S. middle-market business.
	Total purchase consideration for acquisitions made during the first three months of 2014 was $444 million, which consisted of cash paid of $331 million and deferred purchase and estimated contingent consideration of $113 million. Contingent consideration arrangements are primarily based on EBITDA and revenue targets over periods ranging from two to four years. The fair value of the contingent consideration was based on projected revenue and earnings of the acquired entities. The estimated fair values of assets acquired and liabilities assumed are subject to adjustment when purchase accounting is finalized. The Company also paid $6 million of deferred purchase consideration and $30 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 the first quarter of 2014 based on their fair values:
	For the Three Months Ended March 31, 2014
	(Amounts in millions)
	Cash	$	331
	Estimated fair value of deferred/contingent consideration	113
	Total Consideration	$	444
	Allocation of purchase price:
	Cash and cash equivalents	$	18
	Accounts receivable, net	3
	Other current assets	—
	Property, plant, and equipment	3
	Intangible assets	189
	Goodwill	267
	Other assets	2
	Total assets acquired	482
	Current liabilities	33
	Other liabilities	5
	Total liabilities assumed	38
	Net assets acquired	$	444
	Prior Year Acquisitions
	The Risk and Insurance segment completed six acquisitions during 2013.
	•	June - Marsh acquired Rehder y Asociados Group, an insurance adviser in Peru. The business includes the insurance broker Rehder y Asociados and employee health and benefits specialist, Humanasalud. Marsh also completed the acquisition of Franco & Acra Tecniseguros, an insurance advisor in the Dominican Republic.
	•	July - Guy Carpenter acquired Smith Group, a specialist disability reinsurance risk manager and consultant based in Maine.
	•	September - Marsh purchased an additional stake in Insia a.s., an insurance broker operating in the Czech Republic and Slovakia which, when combined with its prior holdings, gave MMC a controlling interest. Insia a.s. was previously accounted for under the equity method.
	•	November - Marsh & McLennan Agency ("MMA") acquired Elsey & Associates, a Texas-based provider of surety bonds and insurance coverage to the construction industry.
	•	December - MMA acquired Cambridge Property and Casualty, a Michigan-based company providing insurance and risk management services to high net worth individuals and mid-sized businesses.
	The MMA acquisitions were made to expand Marsh's presence in the U.S. middle-market business.
	The Consulting segment completed two acquisitions during 2013.
	•	July - Oliver Wyman acquired Corven, a U.K.-based management consultancy firm.
	•	August - Mercer acquired Global Remuneration Solutions, a market leading compensation consulting firm based in South Africa.
	Pro-Forma Information
	While the Company does not believe its acquisitions are material in the aggregate, the following unaudited pro-forma financial data gives effect to the acquisitions made by the Company during the first three months of 2014 and 2013. In accordance with accounting guidance related to pro-forma disclosure, the information presented for 2014 acquisitions is as if they occurred on January 1, 2013 and reflects acquisitions made in 2013 as if they occurred on January 1, 2012. The 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
			March 31,
	(In millions, except per share figures)		2014		2013
	Revenue		$	3,277	$	3,187
	Income from continuing operations		$	460	$	416
	Net income attributable to the Company		$	446	$	417
	Basic net income per share:
	– Continuing operations		$	0.82	$	0.74
	– Net income attributable to the Company		$	0.81	$	0.76
	Diluted net income per share:
	– Continuing operations		$	0.8	$	0.73
	– Net income attributable to the Company		$	0.8	$	0.75
	The consolidated statements of income include the results of operations of acquired companies since their respective acquisition dates. The consolidated statement of income for the three-month period ending March 31, 2014 includes approximately $21 million of revenue and $1 million of net operating income related to acquisitions made in 2014.

Dispositions

Dispositions	3 Months Ended
	Mar. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]	'
Dispositions	'
	Dispositions
	Summarized Statements of Income data for discontinued operations is as follows:
		Three Months Ended
		March 31,
	(In millions of dollars, except per share figures)	2014			2013
	Disposals of discontinued operations	$	—		$	1
	Income tax expense (credit)	1			(11		)
	Disposals of discontinued operations, net of tax	(1		)	12
	Discontinued operations, net of tax	$	(1	)	$	12
	Discontinued operations, net of tax per share
	– Basic	$	—		$	0.02
	– Diluted	$	—		$	0.02
	The credits in discontinued operations for the three months ended March 31, 2013 primarily result from tax indemnities related to the Putnam sale.

Goodwill_and_Other_Intangibles

Goodwill and Other Intangibles	3 Months Ended
	Mar. 31, 2014
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 test 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. Fair values of the reporting units are estimated using either a market approach or a discounted cash flow model. This fair value determination was categorized as Level 3 in the fair value hierarchy. Carrying values for the reporting units are based on balances at the prior quarter end and include directly identified assets and liabilities as well as an allocation of those assets and liabilities not recorded at the reporting unit level. The Company completed its 2013 annual review in the third quarter of 2013 and concluded goodwill was not impaired, as the fair value of each reporting unit exceeded its carrying value by a substantial margin.
	Other intangible assets that are not deemed to have an indefinite life are amortized over their estimated lives and reviewed for impairment upon the occurrence of certain triggering events in accordance with applicable accounting literature.
	Changes in the carrying amount of goodwill are as follows:
	March 31,
	(In millions of dollars)	2014			2013
	Balance as of January 1, as reported	$	6,893		$	6,792
	Goodwill acquired	267			—
	Other adjustments(a)	(1		)	(40		)
	Balance at March 31,	$	7,159		$	6,752
	(a)	Primarily reflects the impact of foreign exchange in each period.
	Goodwill allocable to the Company’s reportable segments at March 31, 2014 is as follows: Risk & Insurance Services, $4.9 billion and Consulting, $2.2 billion.
	Amortized intangible assets consist of the cost of client lists, client relationships and trade names acquired. The gross cost and accumulated amortization are as follows:
		March 31, 2014								December 31, 2013
	(In millions of dollars)	Gross			Accumulated			Net		Gross		Accumulated		Net
		Cost			Amortization			Carrying		Cost		Amortization		Carrying
								Amount						Amount
	Amortized intangibles	$	1,079		$	439		$	640	$	888	$	416	$	472
	Aggregate amortization expense for the three months ended March 31, 2014 and 2013 was $22 million and $18 million, respectively. The estimated future aggregate amortization expense is as follows:
	For the Years Ending December 31,
	(In millions of dollars)	Estimated Expense
	2014 (excludes amortization through March 31, 2014)	$	82
	2015	102
	2016	97
	2017	90
	2018	89
	Subsequent years	180
		$	640

Fair_Value_Measurements

Fair Value Measurements	3 Months Ended
	Mar. 31, 2014
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 Financial Accounting Standards Board ("FASB") in Accounting Standards Council ("ASC") Topic No. 820 ("Fair Value Measurements and Disclosures"). 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 money market mutual funds).
	Assets and liabilities utilizing Level 1 inputs include exchange-traded equity securities and mutual funds.
	Level 2.	Assets and liabilities whose values are based on the following:
	a)	Quoted prices for similar assets or liabilities in active markets;
	b)	Quoted prices for identical or similar assets or liabilities in non-active markets (examples include corporate and municipal bonds, which trade infrequently);
	c)	Pricing models whose inputs are observable for substantially the full term of the asset or liability (examples include most over-the-counter derivatives, including interest rate and currency swaps); and
	d)	Pricing models whose inputs are derived principally from or corroborated by observable market data through correlation or other means for substantially the full asset or liability (for example, certain mortgage loans).
	Assets and liabilities utilizing Level 2 inputs include corporate and municipal bonds, senior notes and interest rate swaps.
	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 (examples include private equity investments, certain commercial mortgage whole loans, and long-dated or complex derivatives including certain foreign exchange options and long-dated options on gas and power).
	Liabilities utilizing Level 3 inputs include liabilities for contingent purchase consideration.
	Valuation Techniques
	Equity Securities and Mutual Funds - Level 1
	Investments for which market quotations are readily available are valued at the sale price on their principal exchange, or official closing bid price for certain markets.
	Interest Rate Swap Derivatives - Level 2
	The fair value of interest rate swap derivatives is based on the present value of future cash flows at each valuation date resulting from utilization of the swaps, using a constant discount rate of 1.6% compared to discount rates based on projected future yield curves (See Note 12).
	Senior Notes due 2014 - Level 2
	The fair value of the first $250 million of Senior Notes maturing in 2014 is estimated to be the carrying value of those notes based on discounted future cash flows using current interest rates available for debt with similar terms and remaining maturities, adjusted by the fair value of the interest rate swap derivatives, discussed above. In the first quarter of 2011, the Company entered into two interest rate swaps to convert interest on a portion of its Senior Notes from a fixed rate to a floating rate. The swaps are designated as fair value hedging instruments. The change in the fair value of the swaps is recorded on the balance sheet. The carrying value of the debt related to these swaps is adjusted by an equal amount (See Note 12).
	Contingent Consideration Liability - Level 3
	Purchase consideration for some acquisitions made by the Company includes contingent consideration arrangements. Contingent consideration arrangements are primarily based on meeting EBITDA and revenue targets over periods ranging from two to four years. The fair value of contingent consideration is estimated as the present value of future cash flows resulting from the projected revenue and earnings 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 March 31, 2014 and December 31, 2013.
		Identical Assets						Observable Inputs				Unobservable				Total
		(Level 1)						(Level 2)				Inputs
												(Level 3)
	(In millions of dollars)	3/31/14			12/31/13			3/31/14		12/31/13		3/31/14		12/31/13		3/31/14		12/31/13
	Assets:
	Financial instruments owned:
	Mutual funds(a)	$	144		$	154		$	—	$	—	$	—	$	—	$	144	$	154
	Money market funds(b)	66			45			—		—		—		—		66		45
	Interest rate swap derivatives(c)	—			—			2		3		—		—		2		3
	Total assets measured at fair value	$	210		$	199		$	2	$	3	$	—	$	—	$	212	$	202
	Fiduciary Assets:
	Money market funds	$	14		$	—		$	—	$	—	$	—	$	—	$	14	$	—
	Total fiduciary assets measured	$	14		$	—		$	—	$	—	$	—	$	—	$	14	$	—
	at fair value
	Liabilities:
	Contingent purchase	$	—		$	—		$	—	$	—	$	133	$	104	$	133	$	104
	consideration liability(d)
	Senior Notes due 2014(e)	—			—			252		253		—		—		252		253
	Total liabilities measured at fair value	$	—		$	—		$	252	$	253	$	133	$	104	$	385	$	357
	(a)	Included in other assets in the consolidated balance sheets.
	(b)	Included in cash and cash equivalents in the consolidated balance sheets.
	(c)	Included in other receivables in the consolidated balance sheets.
	(d)	Included in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.
	(e)	Included in long-term debt in the consolidated balance sheets.
	During the three-month period ended March 31, 2014, there were no assets or liabilities that were transferred between Level 1 and Level 2 or between Level 2 and Level 3.
	The table below sets forth a summary of the changes in fair value of the Company’s Level 3 liabilities as of March 31, 2014 and 2013 that represent contingent consideration related to acquisitions:
	(In millions of dollars)	2014			2013
	Balance at January 1,	$	104		$	63
	Additions	55			—
	Payments	(30		)	(3		)
	Revaluation Impact	4			1
	Balance at March 31,	$	133		$	61
	The fair value of the contingent liability is based on projections of revenue and earnings for the acquired entities that are 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 $4 million in the three-month period ended March 31, 2014. A 5% increase in the above mentioned projections would increase the liability by approximately $17 million. A 5% decrease in the above mentioned projections would decrease the liability by approximately $19 million.
	Fair Value of Long-term Investments
	The Company has certain long-term investments, primarily investments in non-publicly traded private equity funds, of $13 million and $14 million at March 31, 2014 and December 31, 2013, respectively, carried on the cost basis for which there are no readily available market prices. The carrying values of these investments approximates their fair value. Management's estimate of the fair value of these non-publicly traded investments is based on valuation methodologies including estimates from private equity managers of the fair value of underlying investments in private equity funds. The ability to accurately predict future cash flows, revenue or earnings may impact the determination of fair value. The Company monitors these investments for impairment and makes appropriate reductions in carrying values when necessary. If carried at fair value, these investments would be classified as Level 3 in the fair value hierarchy. They are included in Other assets in the consolidated balance sheets.

Retirement_Benefits

Retirement Benefits	3 Months Ended
	Mar. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Retirement Benefits	'
	Retirement Benefits
	The Company maintains qualified and non-qualified defined benefit pension plans for its U.S. and non-U.S. eligible employees. The Company’s policy for funding its tax qualified defined benefit retirement plans is to contribute amounts at least sufficient to meet the funding requirements set forth by U.S. law and the laws of the non-U.S. jurisdictions in which the Company offers defined benefit plans.
	The target asset allocation for the U.S. Plan is 58% equities and equity alternatives and 42% fixed income. As of March 31, 2014, the actual allocation for the U.S. Plan was 62% equities and equity alternatives and 38% fixed income. The target asset allocation for the U.K. Plans, which comprises approximately 82% of non-U.S. Plan assets, is 50% equities and equity alternatives and 50% fixed income. As of March 31, 2014, the actual allocation for the U.K. Plan was 48% equities and equity alternatives and 52% fixed income. 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.
	After completion of a consultation period with affected colleagues, in January 2014, the Company amended its U.K. defined benefit pension plans to close those plans to future benefit accruals effective August 1, 2014 and will replace those plans, along with its existing defined contribution plans, with a new, comprehensive defined contribution arrangement. This change resulted in a curtailment of the U.K. defined benefit plans, and as required under GAAP, the Company re-measured the defined benefit plans’ assets and liabilities at the amendment date, based on assumptions and market conditions at that date. As a result of the re-measurement, the projected benefit obligation ("PBO") increased by approximately $147 million and the funded status decreased by approximately $137 million. The change in the PBO and in the funded status relates primarily to a decrease in the discount rate at the re-measurement date. The net periodic benefit costs recognized in 2014 are the weighted average resulting from the December 31, 2013 measurement and the January 2014 re-measurement. The Company recognized a curtailment gain of $65 million in the first quarter of 2014, primarily resulting from the recognition of the remaining unamortized prior service credit related to a plan amendment made in December 2012. This gain was mostly offset by the cost of a transition benefit for certain employees most impacted by the amendment, which is not part of net periodic pension cost.
	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								Postretirement
	For the Three Months Ended March 31,	Benefits								Benefits
	(In millions of dollars)	2014				2013				2014			2013
	Service cost	$	61			$	64			$	1		$	2
	Interest cost	161				145				3			3
	Expected return on plan assets	(248		)		(228		)		—			—
	Amortization of prior service credit	(3		)		(5		)		—			—
	Recognized actuarial loss	51				78				—			—
	Net periodic benefit cost	$	22			$	54			$	4		$	5
	Curtailment (credit)	(65		)		—				—			—
	Total cost (credit)	$	(43	)		$	54			$	4		$	5
	U.S. Plans only	Pension								Postretirement
	For the Three Months Ended March 31,	Benefits								Benefits
	(In millions of dollars)	2014				2013				2014			2013
	Service cost	$	22			$	27			$	—		$	1
	Interest cost	63				57				2			2
	Expected return on plan assets	(86		)		(81		)		—			—
	Amortization of prior service credit	(2		)		(4		)		—			—
	Recognized actuarial loss (gain)	26				51				—			—
	Net periodic benefit cost (credit)	$	23			$	50			$	2		$	3
	Significant non-U.S. Plans only	Pension								Postretirement
	For the Three Months Ended March 31,	Benefits								Benefits
	(In millions of dollars)	2014				2013				2014			2013
	Service cost	$	39			$	37			$	1		$	1
	Interest cost	98				88				1			1
	Expected return on plan assets	(162		)		(147		)		—			—
	Amortization of prior service cost	(1		)		(1		)		—			—
	Recognized actuarial loss	25				27				—			—
	Net periodic benefit cost	$	(1	)		$	4			$	2		$	2
	Curtailment (credit)	(65		)		—				—			—
	Total cost (credit)	$	(66	)		$	4			$	2		$	2
	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						Postretirement
		Benefits						Benefits
	March 31,	2014			2013			2014			2013
	Weighted average assumptions:
	Expected return on plan assets	7.53	%		7.66	%		—	%		—	%
	Discount rate	4.74	%		4.38	%		5.03	%		4.32	%
	Rate of compensation increase	2.64	%		2.43	%		—	%		—	%
	The Company made approximately $54 million of contributions to its U.S. and non-U.S. defined benefit plans in the first three months of 2014. The Company expects to contribute approximately $130 million to its non-qualified U.S. pension and non-U.S. pension plans during the remainder of 2014.

Debt

Debt	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	The Company’s outstanding debt is as follows:
	(In millions of dollars)	March 31,			December 31,
		2014			2013
	Short-term:
	Commercial paper	$	100		$	—
	Current portion of long-term debt	332			334
		432			334
	Long-term:
	Senior notes – 5.875% due 2033	297			297
	Senior notes – 5.375% due 2014	322			323
	Senior notes – 5.75% due 2015	230			230
	Senior notes – 2.30% due 2017	249			249
	Senior notes – 9.25% due 2019	399			399
	Senior notes – 4.80% due 2021	497			497
	Senior notes – 2.55% due 2018	248			248
	Senior notes – 4.05% due 2023	247			247
	Mortgage – 5.70% due 2035	410			413
	Term Loan Facility - due 2016	50			50
	Other	2			2
		2,951			2,955
	Less current portion	332			334
		$	2,619		$	2,621
	The senior notes in the table above are publicly registered by the Company with no guarantees attached.
	In September 2013, the Company issued $250 million of 2.55% five-year senior notes and $250 million of 4.05% ten-year senior notes. The net proceeds of this offering were used for general corporate purposes, which included a partial redemption of $250 million of the outstanding principal amount of the existing 5.75% senior notes due 2015. The redemption settled in October 2013 with a total cash outflow of approximately $275 million including a $24 million cost for early redemption.
	In February 2013, the Company repaid its 4.850% fixed rate $250 million senior notes.
	The Company had $100 million of commercial paper outstanding at March 31, 2014 with a weighted average interest rate of 0.32% including dealer fees.
	On March 28, 2014, the Company and certain of its foreign subsidiaries amended its $1.0 billion facility as discussed below into a $1.2 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 March 2019 and requires the Company to maintain certain coverage and leverage ratios which are tested quarterly. There were no borrowings outstanding under this facility at March 31, 2014.
	The Company and certain of its foreign subsidiaries previously maintained a $1.0 billion multi-currency five-year revolving credit facility. The facility was previously due to expire in October 2016 and was in effect until March 2014. There were no borrowings outstanding under this facility at the time it was amended.
	In December 2012, the Company closed on a $50 million, three-year term loan facility. The interest rate on this facility at March 31, 2014 was 1.28%, which is based on LIBOR plus a fixed margin which varies with the Company's credit ratings. The facility requires the Company to maintain coverage ratios and leverage ratios consistent with the revolving credit facility discussed above. The Company had $50 million of borrowings under this facility at March 31, 2014.
	Derivative Financial Instruments
	In February 2011, the Company entered into two $125 million 3.5-year interest rate swaps to hedge changes in the fair value of the first $250 million of the outstanding 5.375% senior notes due in 2014.
	Under the terms of the swaps, the counter-parties will pay the Company a fixed rate of 5.375% and the Company will pay interest at a floating rate of three-month LIBOR plus a fixed spread of 3.726%. The maturity date of the senior notes and the swaps match exactly. The floating rate resets quarterly, with every second reset occurring on the interest payment date of the senior notes. The swaps net settle every six months on the senior note coupon payment dates. The swaps are designated as fair value hedging instruments and are deemed to be perfectly effective in accordance with applicable accounting guidance. The fair value of the swaps at inception was zero and subsequent changes in the fair value of the interest rate swaps are reflected in the carrying value of the interest rate swaps and in the consolidated balance sheet. The carrying value of the debt on the balance sheet was adjusted by an equal amount. The gain or (loss) on the hedged item (fixed rate debt) and the offsetting gain or (loss) on the interest rate swaps for the year-to-date periods ended March 31, 2014 and 2013 are as follows:
		2014							2013
	Income statement classification                (In millions of dollars)	Loss on Swaps			Gain on Notes		Net Income Effect		Loss on Swaps			Gain on Notes		Net Income Effect
	Other Operating Expenses	$	(1	)	$	1	$	—	$	(1	)	$	1	$	—
	The amounts earned and owed under the swap agreements are accrued each period and are reported in interest expense. There was no ineffectiveness recognized in the periods presented.
	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.
		March 31, 2014					December 31, 2013
	(In millions of dollars)	Carrying			Fair		Carrying		Fair
		Amount			Value		Amount		Value
	Short-term debt	$	432		$	439	$	334	$	334
	Long-term debt	$	2,619		$	2,844	$	2,621	$	2,819
	The fair value of the Company’s short-term debt, which consists primarily of term debt maturing within the next year, 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	3 Months Ended
	Mar. 31, 2014
Restructuring and Related Activities [Abstract]	'
Restructuring Costs	'
	Restructuring Costs
	The Company recorded total restructuring costs of $2 million in the first three months of 2014 primarily for future rent under non-cancelable leases. These costs were incurred in Corporate.
	Details of the restructuring activity from January 1, 2013 through March 31, 2014, which includes liabilities from actions prior to 2014, are as follows:
	(In millions of dollars)	Liability at 1/1/13		Amounts		Cash			Other			Liability at 12/31/13		Amounts		Cash			Liability at 3/31/14
				Accrued		Paid								Accrued		Paid
	Severance	$	36	$	9	$	(33	)	$	(1	)	$	11	$	—	$	(3	)	$	8
	Future rent under non-cancelable leases and other costs	134		13		(32		)	(2		)	113		2		(12		)	103
	Total	$	170	$	22	$	(65	)	$	(3	)	$	124	$	2	$	(15	)	$	111
	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, other liabilities, or accrued compensation, depending on the nature of the items.

Common_Stock

Common Stock	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Common Stock	'
	Common Stock
	During the first three months of 2014, the Company repurchased approximately 2 million shares of its common stock for consideration of $100 million. In May 2013, the Board of Directors of the Company authorized share repurchases of up to $1 billion of the Company's common stock. The Company remains authorized to purchase additional shares of its common stock up to a value of $463 million. There is no time limit on the authorization. During the first three months of 2013, the Company repurchased 2.7 million shares of its common stock for consideration of $100 million.

Claims_Lawsuits_And_Other_Cont

Claims, Lawsuits And Other Contingencies	3 Months Ended
	Mar. 31, 2014
Commitments and Contingencies Disclosure [Abstract]	'
Claims, Lawsuits, and Other Contingencies	'
	Claims, Lawsuits and Other Contingencies
	Errors and Omissions Claims
	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, and the provision of consulting services relating to the drafting and interpretation of trust deeds and other documentation governing pension plans. Errors and omissions claims may seek damages, including punitive and treble damages, in amounts that could, if awarded, be significant. In establishing liabilities for errors and omissions claims in accordance with FASB ASC Subtopic No. 450-20 (Contingencies-Loss Contingencies), the Company utilizes case level reviews by inside and outside counsel, an internal actuarial analysis and other analysis 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 Related Claims
	In January 2005, the Company and its subsidiary Marsh Inc. entered into a settlement agreement with the New York State Attorney General (“NYAG”) and the New York State Insurance Department to settle a civil complaint and related citation regarding Marsh's use of market service agreements with various insurance companies. The parties subsequently entered into an amended and restated settlement agreement in February 2010 that restored a level playing field for Marsh.
	Numerous private party lawsuits based on similar allegations to those made in the NYAG complaint were commenced against the Company, one or more of its subsidiaries, and their current and former directors and officers. The vast majority of these matters have been resolved. Two actions instituted by policyholders against the Company, Marsh and certain Marsh subsidiaries remain pending.
	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. In the ordinary course of business the Company is also subject to subpoenas, investigations, lawsuits and/or other regulatory actions undertaken by governmental authorities. In this regard, in November 2013, Mercer received a subpoena from the New York Department of Financial Services in connection with a review of New York’s public pension funds.
	Other Contingencies-Guarantees
	In connection with its acquisition of U.K.-based Sedgwick Group in 1998, the Company acquired several insurance underwriting businesses that were already in run-off, including River Thames Insurance Company Limited (“River Thames”), which the Company sold in 2001. Sedgwick guaranteed payment of claims on certain policies underwritten through the Institute of London Underwriters (the “ILU”) by River Thames. The policies covered by this guarantee are 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 March 31, 2014, 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 us 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 we anticipate that additional claimants may seek to recover against the letter of credit.
	Kroll-related Matters
	Under the terms of a stock purchase agreement with Altegrity, Inc. (“Altegrity”) related to Altegrity's purchase of Kroll from the Company in August 2010, a copy of which is attached as an exhibit to the Company's Quarterly Report on Form 10-Q for the period ended June 30, 2010, the Company agreed to provide a limited indemnity to Altegrity with respect to certain Kroll-related litigation and regulatory matters.
	The pending proceedings and other matters described in this Note 15 on Claims, Lawsuits and Other Contingencies may expose the Company or its subsidiaries to liability for significant monetary damages and other forms of relief. Where a loss is both probable and reasonably estimable, the Company establishes liabilities in accordance with FASB ASC Subtopic No. 450-20 (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	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Segment Information	'
	Segment Information
	The Company is organized based on the types of services provided. Under this organizational structure, the Company’s business 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 2013 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-month periods ended March 31, 2014 and 2013 are as follows:
			Three Months Ended
			March 31,
	(In millions of dollars)		Revenue				Operating
							Income
							(Loss)
	2014 –
	Risk and Insurance Services		$	1,839		(a)	$	493
	Consulting		1,432			(b)	225
	Total Operating Segments		3,271				718
	Corporate / Eliminations		(7		)		(45		)
	Total Consolidated		$	3,264			$	673
	2013–
	Risk and Insurance Services		$	1,771		(a)	$	468
	Consulting		1,362			(b)	187
	Total Operating Segments		3,133				655
	Corporate / Eliminations		(7		)		(48		)
	Total Consolidated		$	3,126			$	607
	(a)	Includes interest income on fiduciary funds of $6 million and $8 million in 2014 and 2013, respectively, and equity method income of $1 million in 2013, respectively.
	(b)	Includes inter-segment revenue of $7 million in both 2014 and 2013 and interest income on fiduciary funds of $1 million in both 2014 and 2013.
	Details of operating segment revenue for the three-month periods ended March 31, 2014 and 2013 are as follows:
			Three Months Ended
			March 31,
	(In millions of dollars)		2014				2013
	Risk and Insurance Services
	Marsh		$	1,457			$	1,395
	Guy Carpenter		382				376
	Total Risk and Insurance Services		1,839				1,771
	Consulting
	Mercer		1,061				1,041
	Oliver Wyman Group		371				321
	Total Consulting		1,432				1,362
	Total Operating Segments		3,271				3,133
	Corporate/ Eliminations		(7		)		(7		)
	Total		$	3,264			$	3,126

New_Accounting_Guidance

New Accounting Guidance	3 Months Ended
	Mar. 31, 2014
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]	'
New Accounting Guidance	'
	New Accounting Guidance
	In April 2014, the FASB issued new accounting guidance which changes the criteria for reporting discontinued operations and enhancing disclosures in this area. Under the new guidance, only disposals representing a strategic shift in operations, such as disposal of a major geographic area or a major line of business, should be presented as discontinued operations. Those strategic shifts should have a major impact on the organization's operations and financial results. In addition, the new guidance requires expanded disclosures about discontinued operations. The guidance is effective for fiscal years beginning on or after December 15, 2014. Adoption of the guidance is not expected to materially affect the Company's financial position, results of operations or cash flows.
	In July 2013, the FASB issued new accounting guidance related to the presentation of unrecognized tax benefits as a reduction to a deferred tax asset for a net operating loss carry-forward, a similar tax loss, or a tax credit carry-forward. However, to the extent a net operating loss carry-forward, a similar tax loss, or a tax credit carry-forward is not available at the reporting date under the tax law of the applicable jurisdiction, the unrecognized tax benefit shall be presented in the financial statement as a liability and shall not be combined with deferred tax assets. The guidance is effective for fiscal years beginning after December 15, 2013. The adoption of this new guidance did not have a material impact on the Company's financial statements.
	In July 2013, the FASB issued new accounting guidance which amends the criteria for an entity to qualify as an investment company. The guidance clarifies the characteristics of an investment company, provides comprehensive guidance to determine whether an entity is an investment company and sets measurement and disclosure requirements for investment companies. The guidance is effective for interim and annual reporting periods beginning after December 13, 2013. The adoption of this new guidance did not have a material impact on the Company's financial statements.

Principles_of_Consolidation_an1

Principles of Consolidation and Other Matters (Policies)	3 Months Ended
	Mar. 31, 2014
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
	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.
Income Taxes	'
	The Company's effective tax rate in the first quarter of 2014 was 29.5%. The rate reflects the impact of non-U.S. earnings subject to tax at rates below the U.S. statutory rate, including the effect of repatriation. The effective tax rate for the first quarter of 2013 was 29.9%.
	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.
Reclassifications	'
	In the first quarter of 2014, the Company enhanced its operating cash flow presentation within the statement of cash flows to show on single lines the impact of pension and other benefit plan contributions in excess of the related expenses, and the non-cash impact of equity share awards. Previously, the cash flow impact of those items was presented as part of changes in other assets and other liabilities, and changes in other liabilities, respectively. The prior year’s presentation was conformed to the current presentation for the following line items within operating cash flows:
	•	Share based compensation expense
	•	Changes in other assets
	•	Contributions to pension and other benefit plans in excess of current year expense/credit
	•	Changes in other liabilities
Fair Value Hierarchy	'
	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 Financial Accounting Standards Board ("FASB") in Accounting Standards Council ("ASC") Topic No. 820 ("Fair Value Measurements and Disclosures"). 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 money market mutual funds).
	Assets and liabilities utilizing Level 1 inputs include exchange-traded equity securities and mutual funds.
	Level 2.	Assets and liabilities whose values are based on the following:
	a)	Quoted prices for similar assets or liabilities in active markets;
	b)	Quoted prices for identical or similar assets or liabilities in non-active markets (examples include corporate and municipal bonds, which trade infrequently);
	c)	Pricing models whose inputs are observable for substantially the full term of the asset or liability (examples include most over-the-counter derivatives, including interest rate and currency swaps); and
	d)	Pricing models whose inputs are derived principally from or corroborated by observable market data through correlation or other means for substantially the full asset or liability (for example, certain mortgage loans).
	Assets and liabilities utilizing Level 2 inputs include corporate and municipal bonds, senior notes and interest rate swaps.
	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 (examples include private equity investments, certain commercial mortgage whole loans, and long-dated or complex derivatives including certain foreign exchange options and long-dated options on gas and power).
	Liabilities utilizing Level 3 inputs include liabilities for contingent purchase consideration.
	Valuation Techniques
	Equity Securities and Mutual Funds - Level 1
	Investments for which market quotations are readily available are valued at the sale price on their principal exchange, or official closing bid price for certain markets.
	Interest Rate Swap Derivatives - Level 2
	The fair value of interest rate swap derivatives is based on the present value of future cash flows at each valuation date resulting from utilization of the swaps, using a constant discount rate of 1.6% compared to discount rates based on projected future yield curves (See Note 12).
	Senior Notes due 2014 - Level 2
	The fair value of the first $250 million of Senior Notes maturing in 2014 is estimated to be the carrying value of those notes based on discounted future cash flows using current interest rates available for debt with similar terms and remaining maturities, adjusted by the fair value of the interest rate swap derivatives, discussed above. In the first quarter of 2011, the Company entered into two interest rate swaps to convert interest on a portion of its Senior Notes from a fixed rate to a floating rate. The swaps are designated as fair value hedging instruments. The change in the fair value of the swaps is recorded on the balance sheet. The carrying value of the debt related to these swaps is adjusted by an equal amount (See Note 12).
	Contingent Consideration Liability - Level 3
	Purchase consideration for some acquisitions made by the Company includes contingent consideration arrangements. Contingent consideration arrangements are primarily based on meeting EBITDA and revenue targets over periods ranging from two to four years. The fair value of contingent consideration is estimated as the present value of future cash flows resulting from the projected revenue and earnings of the acquired entities.

Per_Share_Data_Tables

Per Share Data (Tables)	3 Months Ended
	Mar. 31, 2014
Earnings Per Share [Abstract]	'
Diluted EPS Calculation Continuing Operations	'
	Basic and Diluted EPS Calculation - Continuing Operations	Three Months Ended
		March 31,
	(In millions, except per share figures)	2014		2013
	Net income from continuing operations	$	457	$	412
	Less: Net income attributable to non-controlling interests	13		11
		$	444	$	401
	Basic weighted average common shares outstanding	548		548
	Dilutive effect of potentially issuable common shares	8		9
	Diluted weighted average common shares outstanding	556		557
	Average stock price used to calculate common stock equivalents	$	47.84	$	36.21

Recovered_Sheet1

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Tables)	3 Months Ended
	Mar. 31, 2014
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 three-month periods ended March 31, 2014 and 2013.
	(In millions of dollars)	2014			2013
	Assets acquired, excluding cash	$	464		$	—
	Liabilities assumed	(38		)	—
	Contingent/deferred purchase consideration	(113		)	—
	Net cash outflow for current year acquisitions	313			—
	Deferred purchase consideration from prior years' acquisitions	6			1
	Net cash outflow for acquisitions	$	319		$	1
	(In millions of dollars)	2014			2013
	Interest paid	$	44		$	59
	Income taxes paid	$	120		$	85

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	3 Months Ended
	Mar. 31, 2014
Equity [Abstract]	'
Schedule of Accumulated Other Comprehensive Income (Loss)	'
	The changes in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the three-month periods ended March 31, 2014 and 2013, including amounts reclassified out of AOCI, are as follows:
	(In millions of dollars)	Unrealized Investment Gains				Pension/Post-Retirement Plans Gains (Losses)				Foreign Currency Translation Adjustments				Total
	Balance as of January 1, 2014	$	5			$	(2,682	)		$	56			$	(2,621	)
	Other comprehensive income (loss) before reclassifications	—				(199		)		78				(121		)
	Amounts reclassified from accumulated other comprehensive income	—				34				—				34
	Net current period other comprehensive income (loss)	—				(165		)		78				(87		)
	Balance as of March 31, 2014	$	5			$	(2,847	)		$	134			$	(2,708	)
	(In millions of dollars)	Unrealized Investment Gains				Pension/Post-Retirement Plans Gains (Losses)				Foreign Currency Translation Adjustments				Total
	Balance as of January 1, 2013	$	4			$	(3,451	)		$	140			$	(3,307	)
	Other comprehensive income (loss) before reclassifications	—				139				(256		)		(117		)
	Amounts reclassified from accumulated other comprehensive income	—				45				—				45
	Net current period other comprehensive income (loss)	—				184				(256		)		(72		)
	Balance as of March 31, 2013	$	4			$	(3,267	)		$	(116	)		$	(3,379	)
Schedule of Components of Comprehensive Income (Loss)	'
	The components of other comprehensive income (loss) for the three-month periods ended March 31, 2014 and 2013 are as follows:
	Three Months Ended March 31,	2014										2013
	(In millions of dollars)	Pre-Tax			Tax			Net of Tax				Pre-Tax			Tax			Net of Tax
	Foreign currency translation adjustments	$	71		$	(7	)	$	78			$	(260	)	$	(4	)	$	(256	)
	Unrealized investment gains (losses)	—			—			—				—			—			—
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains (a)	(3		)	(1		)	(2		)		(6		)	(2		)	(4		)
	Net actuarial losses (a)	51			15			36				78			29			49
	Subtotal	48			14			34				72			27			45
	Effect of remeasurement	(166		)	(33		)	(133		)		—			—			—
	Effect of curtailment	(65		)	(13		)	(52		)		—			—			—
	Foreign currency translation adjustments	(17		)	(2		)	(15		)		180			41			139
	Other	1			—			1				—			—			—
	Pension/post-retirement plans (losses) gains	(199		)	(34		)	(165		)		252			68			184
	Other comprehensive (loss) income	$	(128	)	$	(41	)	$	(87	)		$	(8	)	$	64		$	(72	)
	(a) 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_Tables

Acquisitions (Tables)	3 Months Ended
	Mar. 31, 2014
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 the first quarter of 2014 based on their fair values:
	For the Three Months Ended March 31, 2014
	(Amounts in millions)
	Cash	$	331
	Estimated fair value of deferred/contingent consideration	113
	Total Consideration	$	444
	Allocation of purchase price:
	Cash and cash equivalents	$	18
	Accounts receivable, net	3
	Other current assets	—
	Property, plant, and equipment	3
	Intangible assets	189
	Goodwill	267
	Other assets	2
	Total assets acquired	482
	Current liabilities	33
	Other liabilities	5
	Total liabilities assumed	38
	Net assets acquired	$	444
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
			March 31,
	(In millions, except per share figures)		2014		2013
	Revenue		$	3,277	$	3,187
	Income from continuing operations		$	460	$	416
	Net income attributable to the Company		$	446	$	417
	Basic net income per share:
	– Continuing operations		$	0.82	$	0.74
	– Net income attributable to the Company		$	0.81	$	0.76
	Diluted net income per share:
	– Continuing operations		$	0.8	$	0.73
	– Net income attributable to the Company		$	0.8	$	0.75

Dispositions_Tables

Dispositions (Tables)	3 Months Ended
	Mar. 31, 2014
Discontinued Operations and Disposal Groups [Abstract]	'
Income Statement Data	'
	Summarized Statements of Income data for discontinued operations is as follows:
		Three Months Ended
		March 31,
	(In millions of dollars, except per share figures)	2014			2013
	Disposals of discontinued operations	$	—		$	1
	Income tax expense (credit)	1			(11		)
	Disposals of discontinued operations, net of tax	(1		)	12
	Discontinued operations, net of tax	$	(1	)	$	12
	Discontinued operations, net of tax per share
	– Basic	$	—		$	0.02
	– Diluted	$	—		$	0.02

Goodwill_and_Other_Intangibles1

Goodwill and Other Intangibles (Tables)	3 Months Ended
	Mar. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]	'
Changes in the Carrying Amount of Goodwill	'
	Changes in the carrying amount of goodwill are as follows:
	March 31,
	(In millions of dollars)	2014			2013
	Balance as of January 1, as reported	$	6,893		$	6,792
	Goodwill acquired	267			—
	Other adjustments(a)	(1		)	(40		)
	Balance at March 31,	$	7,159		$	6,752
	(a)	Primarily reflects the impact of foreign exchange in each period.
Amortized Intangible Assets	'
	Amortized intangible assets consist of the cost of client lists, client relationships and trade names acquired. The gross cost and accumulated amortization are as follows:
		March 31, 2014								December 31, 2013
	(In millions of dollars)	Gross			Accumulated			Net		Gross		Accumulated		Net
		Cost			Amortization			Carrying		Cost		Amortization		Carrying
								Amount						Amount
	Amortized intangibles	$	1,079		$	439		$	640	$	888	$	416	$	472
Estimated Future Aggregate Amortization Expense	'
	Aggregate amortization expense for the three months ended March 31, 2014 and 2013 was $22 million and $18 million, respectively. The estimated future aggregate amortization expense is as follows:
	For the Years Ending December 31,
	(In millions of dollars)	Estimated Expense
	2014 (excludes amortization through March 31, 2014)	$	82
	2015	102
	2016	97
	2017	90
	2018	89
	Subsequent years	180
		$	640

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2014
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 March 31, 2014 and December 31, 2013.
		Identical Assets						Observable Inputs				Unobservable				Total
		(Level 1)						(Level 2)				Inputs
												(Level 3)
	(In millions of dollars)	3/31/14			12/31/13			3/31/14		12/31/13		3/31/14		12/31/13		3/31/14		12/31/13
	Assets:
	Financial instruments owned:
	Mutual funds(a)	$	144		$	154		$	—	$	—	$	—	$	—	$	144	$	154
	Money market funds(b)	66			45			—		—		—		—		66		45
	Interest rate swap derivatives(c)	—			—			2		3		—		—		2		3
	Total assets measured at fair value	$	210		$	199		$	2	$	3	$	—	$	—	$	212	$	202
	Fiduciary Assets:
	Money market funds	$	14		$	—		$	—	$	—	$	—	$	—	$	14	$	—
	Total fiduciary assets measured	$	14		$	—		$	—	$	—	$	—	$	—	$	14	$	—
	at fair value
	Liabilities:
	Contingent purchase	$	—		$	—		$	—	$	—	$	133	$	104	$	133	$	104
	consideration liability(d)
	Senior Notes due 2014(e)	—			—			252		253		—		—		252		253
	Total liabilities measured at fair value	$	—		$	—		$	252	$	253	$	133	$	104	$	385	$	357
	(a)	Included in other assets in the consolidated balance sheets.
	(b)	Included in cash and cash equivalents in the consolidated balance sheets.
	(c)	Included in other receivables in the consolidated balance sheets.
	(d)	Included in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.
	(e)	Included in long-term debt 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 as of March 31, 2014 and 2013 that represent contingent consideration related to acquisitions:
	(In millions of dollars)	2014			2013
	Balance at January 1,	$	104		$	63
	Additions	55			—
	Payments	(30		)	(3		)
	Revaluation Impact	4			1
	Balance at March 31,	$	133		$	61

Retirement_Benefits_Tables

Retirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2014
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [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								Postretirement
	For the Three Months Ended March 31,	Benefits								Benefits
	(In millions of dollars)	2014				2013				2014			2013
	Service cost	$	61			$	64			$	1		$	2
	Interest cost	161				145				3			3
	Expected return on plan assets	(248		)		(228		)		—			—
	Amortization of prior service credit	(3		)		(5		)		—			—
	Recognized actuarial loss	51				78				—			—
	Net periodic benefit cost	$	22			$	54			$	4		$	5
	Curtailment (credit)	(65		)		—				—			—
	Total cost (credit)	$	(43	)		$	54			$	4		$	5
	U.S. Plans only	Pension								Postretirement
	For the Three Months Ended March 31,	Benefits								Benefits
	(In millions of dollars)	2014				2013				2014			2013
	Service cost	$	22			$	27			$	—		$	1
	Interest cost	63				57				2			2
	Expected return on plan assets	(86		)		(81		)		—			—
	Amortization of prior service credit	(2		)		(4		)		—			—
	Recognized actuarial loss (gain)	26				51				—			—
	Net periodic benefit cost (credit)	$	23			$	50			$	2		$	3
	Significant non-U.S. Plans only	Pension								Postretirement
	For the Three Months Ended March 31,	Benefits								Benefits
	(In millions of dollars)	2014				2013				2014			2013
	Service cost	$	39			$	37			$	1		$	1
	Interest cost	98				88				1			1
	Expected return on plan assets	(162		)		(147		)		—			—
	Amortization of prior service cost	(1		)		(1		)		—			—
	Recognized actuarial loss	25				27				—			—
	Net periodic benefit cost	$	(1	)		$	4			$	2		$	2
	Curtailment (credit)	(65		)		—				—			—
	Total cost (credit)	$	(66	)		$	4			$	2		$	2
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						Postretirement
		Benefits						Benefits
	March 31,	2014			2013			2014			2013
	Weighted average assumptions:
	Expected return on plan assets	7.53	%		7.66	%		—	%		—	%
	Discount rate	4.74	%		4.38	%		5.03	%		4.32	%
	Rate of compensation increase	2.64	%		2.43	%		—	%		—	%

Debt_Tables

Debt (Tables)	3 Months Ended
	Mar. 31, 2014
Debt Disclosure [Abstract]	'
Schedule of Outstanding Debt	'
	The Company’s outstanding debt is as follows:
	(In millions of dollars)	March 31,			December 31,
		2014			2013
	Short-term:
	Commercial paper	$	100		$	—
	Current portion of long-term debt	332			334
		432			334
	Long-term:
	Senior notes – 5.875% due 2033	297			297
	Senior notes – 5.375% due 2014	322			323
	Senior notes – 5.75% due 2015	230			230
	Senior notes – 2.30% due 2017	249			249
	Senior notes – 9.25% due 2019	399			399
	Senior notes – 4.80% due 2021	497			497
	Senior notes – 2.55% due 2018	248			248
	Senior notes – 4.05% due 2023	247			247
	Mortgage – 5.70% due 2035	410			413
	Term Loan Facility - due 2016	50			50
	Other	2			2
		2,951			2,955
	Less current portion	332			334
		$	2,619		$	2,621
Gain Or Loss On The Hedged Item And Offsetting Gain Or Loss On Interest Rate Swaps	'
	The gain or (loss) on the hedged item (fixed rate debt) and the offsetting gain or (loss) on the interest rate swaps for the year-to-date periods ended March 31, 2014 and 2013 are as follows:
		2014							2013
	Income statement classification                (In millions of dollars)	Loss on Swaps			Gain on Notes		Net Income Effect		Loss on Swaps			Gain on Notes		Net Income Effect
	Other Operating Expenses	$	(1	)	$	1	$	—	$	(1	)	$	1	$	—
Estimated Fair Value Of Significant Financial Instruments	'
	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.
		March 31, 2014					December 31, 2013
	(In millions of dollars)	Carrying			Fair		Carrying		Fair
		Amount			Value		Amount		Value
	Short-term debt	$	432		$	439	$	334	$	334
	Long-term debt	$	2,619		$	2,844	$	2,621	$	2,819

Restructuring_Costs_Tables

Restructuring Costs (Tables)	3 Months Ended
	Mar. 31, 2014
Restructuring and Related Activities [Abstract]	'
Restructuring Activities	'
	Details of the restructuring activity from January 1, 2013 through March 31, 2014, which includes liabilities from actions prior to 2014, are as follows:
	(In millions of dollars)	Liability at 1/1/13		Amounts		Cash			Other			Liability at 12/31/13		Amounts		Cash			Liability at 3/31/14
				Accrued		Paid								Accrued		Paid
	Severance	$	36	$	9	$	(33	)	$	(1	)	$	11	$	—	$	(3	)	$	8
	Future rent under non-cancelable leases and other costs	134		13		(32		)	(2		)	113		2		(12		)	103
	Total	$	170	$	22	$	(65	)	$	(3	)	$	124	$	2	$	(15	)	$	111

Segment_Information_Tables

Segment Information (Tables)	3 Months Ended
	Mar. 31, 2014
Segment Reporting [Abstract]	'
Selected Information And Details For MMC's Operating Segments	'
	Selected information about the Company’s operating segments for the three-month periods ended March 31, 2014 and 2013 are as follows:
			Three Months Ended
			March 31,
	(In millions of dollars)		Revenue				Operating
							Income
							(Loss)
	2014 –
	Risk and Insurance Services		$	1,839		(a)	$	493
	Consulting		1,432			(b)	225
	Total Operating Segments		3,271				718
	Corporate / Eliminations		(7		)		(45		)
	Total Consolidated		$	3,264			$	673
	2013–
	Risk and Insurance Services		$	1,771		(a)	$	468
	Consulting		1,362			(b)	187
	Total Operating Segments		3,133				655
	Corporate / Eliminations		(7		)		(48		)
	Total Consolidated		$	3,126			$	607
	(a)	Includes interest income on fiduciary funds of $6 million and $8 million in 2014 and 2013, respectively, and equity method income of $1 million in 2013, respectively.
	(b)	Includes inter-segment revenue of $7 million in both 2014 and 2013 and interest income on fiduciary funds of $1 million in both 2014 and 2013.
Details of Operating Segment Revenue	'
	Details of operating segment revenue for the three-month periods ended March 31, 2014 and 2013 are as follows:
			Three Months Ended
			March 31,
	(In millions of dollars)		2014				2013
	Risk and Insurance Services
	Marsh		$	1,457			$	1,395
	Guy Carpenter		382				376
	Total Risk and Insurance Services		1,839				1,771
	Consulting
	Mercer		1,061				1,041
	Oliver Wyman Group		371				321
	Total Consulting		1,432				1,362
	Total Operating Segments		3,271				3,133
	Corporate/ Eliminations		(7		)		(7		)
	Total		$	3,264			$	3,126

Nature_of_Operations_Details

Nature of Operations (Details)	3 Months Ended
	Mar. 31, 2014
	segment
Segment Reporting Information [Line Items]	'
Number of business segments	2
Consulting Segment [Member]	'
Segment Reporting Information [Line Items]	'
Number of business groups	2

Recovered_Sheet2

Principles Of Consolidation And Other Matters (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'	'	'
Operating funds related to regulatory requirements or as collateral under captive insurance arrangements	$190,000,000	'	'
Effective tax rate	29.50%	29.90%	'
Unrecognized tax benefits	117,000,000	'	128,000,000
Reasonably possible decrease in unrecognized tax benefits	0	'	'
Projection of unrecognized tax benefit in twelve months, upper bound	$27,000,000	'	'

Principles_of_Consolidation_an2

Principles of Consolidation and Other Matters Investment Income (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Trident II [Member]	'	'
Deferred Revenue Arrangement [Line Items]	'	'
Equity method income	'	$20
Trident III [Member] | Performance Fees [Member]	'	'
Deferred Revenue Arrangement [Line Items]	'	'
Recognized deferred performance fees	7	15
Deferred performance fees	35	'
Private Equity Funds [Member] | Trident III [Member]	'	'
Deferred Revenue Arrangement [Line Items]	'	'
Unrealized Gain (Loss) on Investments	$6	'

Fiduciary_Assets_and_Liabiliti1

Fiduciary Assets and Liabilities (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014
			Risk and Insurance Services Segment [Member]	Risk and Insurance Services Segment [Member]	Consulting Segment [Member]	Consulting Segment [Member]	Mercer Consulting Group [Member]
Fiduciary Assets and Liabilities [Line Items]	'	'	'	'	'	'	'
Interest on fiduciary funds	'	'	$6,000,000	$8,000,000	$1,000,000	$1,000,000	'
Net uncollected premiums and claims receivable and payable	8,700,000,000	8,200,000,000	'	'	'	'	'
Assets in trusts or funds for management or trustee fee	'	'	'	'	'	'	$17,000,000,000

Per_Share_Data_Basic_and_Dilut

Per Share Data (Basic and Diluted EPS Calculation Continuing Operations) (Details) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Earnings Per Share [Abstract]	'	'
Net income from continuing operations	$457	$412
Less: Net income attributable to non-controlling interests	13	11
Net income attributable to the Company	$444	$401
Basic weighted average common shares outstanding (in shares)	548	548
Dilutive effect of potentially issuable common shares (in shares)	8	9
Diluted weighted average common shares outstanding (in shares)	556	557
Average stock price used to calculate common stock equivalents (in dollars per share)	$47.84	$36.21
Stock options outstanding (in shares)	21.6	28.9

Supplemental_Disclosures_to_th1

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Supplemental Cash Flow Information [Abstract]	'	'
Non-cash issuance of common stock	$92	$130
Stock-based compensation expense, equity awards	$26	$34

Supplemental_Disclosures_to_th2

Supplemental Disclosures to the Consolidated Statements of Cash Flows (Additional Information Concerning Acquisitions, Interest And Income Taxes Paid) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Supplemental Cash Flow Information [Abstract]	'	'
Assets acquired, excluding cash	$464	$0
Liabilities assumed	-38	0
Contingent/deferred purchase consideration	-113	0
Net cash outflow for current year acquisitions	313	0
Deferred purchase consideration from prior years' acquisitions	6	1
Net cash outflow for acquisitions	319	1
Interest paid	44	59
Income taxes paid	$120	$85

Other_Comprehensive_Income_Los2

Other Comprehensive Income (Loss) (Schedule of Components of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Balance, beginning of period	($2,621)	($3,307)
Other comprehensive income (loss) before reclassifications	-121	-117
Amounts reclassified from accumulated other comprehensive income	34	45
Other comprehensive loss, net of tax	-87	-72
Balance, end of period	-2,708	-3,379
Unrealized Investment Gains [Member]	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Balance, beginning of period	5	4
Other comprehensive income (loss) before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive loss, net of tax	0	0
Balance, end of period	5	4
Pension/Postretirement Plans Gains (Losses) [Member]	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Balance, beginning of period	-2,682	-3,451
Other comprehensive income (loss) before reclassifications	-199	139
Amounts reclassified from accumulated other comprehensive income	34	45
Other comprehensive loss, net of tax	-165	184
Balance, end of period	-2,847	-3,267
Foreign Currency Translation Adjustments [Member]	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'
Balance, beginning of period	56	140
Other comprehensive income (loss) before reclassifications	78	-256
Amounts reclassified from accumulated other comprehensive income	0	0
Other comprehensive loss, net of tax	78	-256
Balance, end of period	$134	($116)

Other_Comprehensive_Income_Los3

Other Comprehensive Income (Loss) (Schedule Of Components Of Comprehensive Income (Loss)) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Equity [Abstract]	'		'
Foreign currency translation adjustments, Pre-Tax	$71		($260)
Foreign currency translation adjustments, Tax	-7		-4
Foreign currency translation adjustments, Net of Tax	78		-256
Unrealized investment gains (losses), Pre-Tax	0		0
Unrealized investment gains (losses), Tax	0		0
Unrealized investment gains (losses), Net of Tax	0		0
Pension/post-retirement plans:	'		'
Prior Service gains, Pre-Tax	-3	[1]	-6	[1]
Prior Service gains, Tax	-1	[1]	-2	[1]
Prior Service gains, Net of Tax	-2	[1]	-4	[1]
Net actuarial loss, Pre-Tax	51	[1]	78	[1]
Net actuarial loss, Tax	15	[1]	29	[1]
Net actuarial loss, Net of Tax	36	[1]	49	[1]
Subtotal, Pre-Tax	48		72
Subtotal, Tax	14		27
Subtotal, Net of Tax	34		45
Effect of remeasurement, Pre-tax	-166		0
Effect of remeasurement, Tax	-33		0
Effect of remeasurement, Net of Tax	-133		0
Effect of curtailment, Pre-tax	-65		0
Effect of curtailment, Tax	-13		0
Effect of curtailment, Net of Tax	-52		0
Foreign currency translation adjustment, Pre-Tax	-17		180
Foreign currency translation adjustment, Tax	-2		41
Foreign currency translation adjustment, Net of Tax	-15		139
Other, Pre-Tax	1		0
Other, Tax	0		0
Other, Net of Tax	1		0
Pension/retiree plans, Pre-Tax	-199		252
Pension/retiree plans, Tax	-34		68
Pension/retiree plans, Net of Tax	-165		184
Other comprehensive income (loss), before tax	-128		-8
Other comprehensive income (loss), Tax	-41		64
Other comprehensive loss, net of tax	($87)		($72)
[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_Details

Acquisitions (Narrative) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2013	Dec. 31, 2013
	acquisition		Minimum [Member]	Maximum [Member]	Current Fiscal Period Acquisitions [Member]	Current Fiscal Period Acquisitions [Member]	Current Fiscal Period Acquisitions [Member]	Prior Fiscal Periods Acquisitions [Member]	Risk and Insurance Services Segment [Member]	Consulting Segment [Member]
						Minimum [Member]	Maximum [Member]		acquisition	acquisition
Business Acquisition [Line Items]	'	'	'	'	'	'	'	'	'	'
Number of acquisitions made (in acquisitions)	6	'	'	'	'	'	'	'	6	2
Total Consideration	$444	'	'	'	$444	'	'	'	'	'
Cash	331	'	'	'	331	'	'	'	'	'
Estimated fair value of deferred/contingent consideration	113	0	'	'	113	'	'	'	'	'
Revenue target period (in years)	'	'	'2 years	'4 years	'	'2 years	'4 years	'	'	'
Deferred purchase consideration from prior years' acquisitions	6	1	'	'	'	'	'	6	'	'
Contingent consideration from prior year's acquisitions	'	'	'	'	'	'	'	30	'	'
Revenue related to acquisitions	'	'	'	'	21	'	'	'	'	'
Operating income related to acquisitions	'	'	'	'	$1	'	'	'	'	'

Acquisitions_Allocation_Of_Acq

Acquisitions (Allocation Of Acquisition Costs) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Business Acquisition [Line Items]	'	'	'	'
Cash	$331	'	'	'
Estimated fair value of deferred/contingent consideration	113	0	'	'
Total Consideration	444	'	'	'
Allocation of purchase price:	'	'	'	'
Goodwill	7,159	6,752	6,893	6,792
Current Fiscal Period Acquisitions [Member]	'	'	'	'
Business Acquisition [Line Items]	'	'	'	'
Cash	331	'	'	'
Estimated fair value of deferred/contingent consideration	113	'	'	'
Total Consideration	444	'	'	'
Allocation of purchase price:	'	'	'	'
Cash and cash equivalents	18	'	'	'
Accounts receivable, net	3	'	'	'
Other current assets	0	'	'	'
Property, plant, and equipment	3	'	'	'
Intangible assets	189	'	'	'
Goodwill	267	'	'	'
Other assets	2	'	'	'
Total assets acquired	482	'	'	'
Current liabilities	33	'	'	'
Other liabilities	5	'	'	'
Total liabilities assumed	38	'	'	'
Net assets acquired	$444	'	'	'

Acquisitions_ProForma_Informat

Acquisitions (Pro-Forma Information) (Details) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Business Combinations [Abstract]	'	'
Revenue	$3,277	$3,187
Income from continuing operations	460	416
Net income attributable to the Company	$446	$417
Basic net income per share:	'	'
Basic net income per share - Continuing operations (in dollars per share)	$0.82	$0.74
Basic net income per share - Net income attributable to the Company (in dollars per share)	$0.81	$0.76
Diluted net income per share:	'	'
Diluted net income per share - Continuing operations (in dollars per share)	$0.80	$0.73
Diluted net income per share - Net income attributable to the Company (in dollars per share)	$0.80	$0.75

Dispositions_Income_Statement_

Dispositions (Income Statement Data) (Details) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'	'
Disposals of discontinued operations	$0	$1
Income tax expense (credit)	1	-11
Disposals of discontinued operations, net of tax	-1	12
Discontinued operations, net of tax	($1)	$12
Discontinued operations, net of tax per share	'	'
- Basic (in dollars per share)	$0	$0.02
- Diluted (in dollars per share)	$0	$0.02

Goodwill_and_Other_Intangibles2

Goodwill and Other Intangibles (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting Information [Line Items]	'	'	'	'
Goodwill	$7,159	$6,752	$6,893	$6,792
Aggregate amortization expense	22	18	'	'
Risk and Insurance Services Segment [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Goodwill	4,900	'	'	'
Consulting Segment [Member]	'	'	'	'
Segment Reporting Information [Line Items]	'	'	'	'
Goodwill	$2,200	'	'	'

Goodwill_and_Other_Intangibles3

Goodwill and Other Intangibles (Changes in the Carrying Amount of Goodwill) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Goodwill [Roll Forward]	'		'
Balance as of January 1, as reported	$6,893		$6,792
Goodwill acquired	267		0
Other adjustments	-1	[1]	-40	[1]
Balance at March 31,	$7,159		$6,752
[1]	Primarily reflects the impact of foreign exchange in each period.

Goodwill_and_Other_Intangibles4

Goodwill and Other Intangibles (Amortized Intangible Assets) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]	'	'
Gross Cost	$1,079	$888
Accumulated Amortization	439	416
Net Carrying Amount	$640	$472

Recovered_Sheet3

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]	'	'
2014 (excludes amortization through March 31, 2014)	$82	'
2015	102	'
2016	97	'
2017	90	'
2018	89	'
Subsequent years	180	'
Net Carrying Amount	$640	$472

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)	3 Months Ended			3 Months Ended				3 Months Ended
	Mar. 31, 2014	Mar. 31, 2011	Feb. 28, 2011	Mar. 31, 2014	Mar. 31, 2014	Mar. 31, 2014	Feb. 28, 2011	Mar. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
		interest_rate_swap	interest_rate_swap	Minimum [Member]	Maximum [Member]	Senior Debt Obligations Due 2014 [Member]	Senior Debt Obligations Due 2014 [Member]	Interest Rate Swap [Member]	Private Equity Funds [Member]	Private Equity Funds [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'	'	'	'	'	'	'	'	'
Fair value interest rate swap discount rate	'	'	'	'	'	'	'	1.60%	'	'
Fair value interest rate swap derivatives	'	'	'	'	'	$250,000,000	$250,000,000	'	'	'
Number of interest rate swaps to convert fixed interest rate on notes to floating rate	'	2	2	'	'	'	'	'	'	'
Revenue target period (in years)	'	'	'	'2 years	'4 years	'	'	'	'	'
Adjustments to acquisition related contingent consideration liability	4,000,000	'	'	'	'	'	'	'	'	'
Increase in fair value of contingent consideration due to 5% increase in projections	17,000,000	'	'	'	'	'	'	'	'	'
Decrease in fair value of contingent consideration due to 5% decrease in projections	19,000,000	'	'	'	'	'	'	'	'	'
Long-term investments, cost basis	'	'	'	'	'	'	'	'	$13,000,000	$14,000,000

Fair_Value_Measurements_Assets

Fair Value Measurements (Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Details) (Fair Value, Measurements, Recurring [Member], USD $)	Mar. 31, 2014		Dec. 31, 2013
In Millions, unless otherwise specified
Financial instruments owned:	'		'
Total assets measured at fair value	$212		$202
Fiduciary Assets:	'		'
Fiduciary assets	14		0
Liabilities:	'		'
Total liabilities measured at fair value	385		357
Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Total assets measured at fair value	210		199
Fiduciary Assets:	'		'
Fiduciary assets	14		0
Liabilities:	'		'
Total liabilities measured at fair value	0		0
Observable Inputs (Level 2) [Member]	'		'
Financial instruments owned:	'		'
Total assets measured at fair value	2		3
Fiduciary Assets:	'		'
Fiduciary assets	0		0
Liabilities:	'		'
Total liabilities measured at fair value	252		253
Unobservable Inputs (Level 3) [Member]	'		'
Financial instruments owned:	'		'
Total assets measured at fair value	0		0
Fiduciary Assets:	'		'
Fiduciary assets	0		0
Liabilities:	'		'
Total liabilities measured at fair value	133		104
Other Assets [Member]	'		'
Financial instruments owned:	'		'
Mutual funds	144	[1]	154	[1]
Other Assets [Member] | Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Mutual funds	144	[1]	154	[1]
Other Assets [Member] | Observable Inputs (Level 2) [Member]	'		'
Financial instruments owned:	'		'
Mutual funds	0	[1]	0	[1]
Other Assets [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Financial instruments owned:	'		'
Mutual funds	0	[1]	0	[1]
Cash and Cash Equivalents [Member]	'		'
Financial instruments owned:	'		'
Money market funds	66	[2]	45	[2]
Cash and Cash Equivalents [Member] | Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Money market funds	66	[2]	45	[2]
Cash and Cash Equivalents [Member] | Observable Inputs (Level 2) [Member]	'		'
Financial instruments owned:	'		'
Money market funds	0	[2]	0	[2]
Cash and Cash Equivalents [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Financial instruments owned:	'		'
Money market funds	0	[2]	0	[2]
Other Receivables [Member]	'		'
Financial instruments owned:	'		'
Interest rate swap derivatives	2	[3]	3	[3]
Other Receivables [Member] | Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Interest rate swap derivatives	0	[3]	0	[3]
Other Receivables [Member] | Observable Inputs (Level 2) [Member]	'		'
Financial instruments owned:	'		'
Interest rate swap derivatives	2	[3]	3	[3]
Other Receivables [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Financial instruments owned:	'		'
Interest rate swap derivatives	0	[3]	0	[3]
Accounts Payable and Accrued Liabilities and Other Liabilities [Member]	'		'
Liabilities:	'		'
Contingent consideration liability	133	[4]	104	[4]
Accounts Payable and Accrued Liabilities and Other Liabilities [Member] | Identical Assets (Level 1) [Member]	'		'
Liabilities:	'		'
Contingent consideration liability	0	[4]	0	[4]
Accounts Payable and Accrued Liabilities and Other Liabilities [Member] | Observable Inputs (Level 2) [Member]	'		'
Liabilities:	'		'
Contingent consideration liability	0	[4]	0	[4]
Accounts Payable and Accrued Liabilities and Other Liabilities [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Liabilities:	'		'
Contingent consideration liability	133	[4]	104	[4]
Long-term Debt [Member] | Senior Debt Obligations Due 2014 [Member]	'		'
Liabilities:	'		'
Senior Notes due 2014	252	[5]	253	[5]
Long-term Debt [Member] | Senior Debt Obligations Due 2014 [Member] | Identical Assets (Level 1) [Member]	'		'
Liabilities:	'		'
Senior Notes due 2014	0	[5]	0	[5]
Long-term Debt [Member] | Senior Debt Obligations Due 2014 [Member] | Observable Inputs (Level 2) [Member]	'		'
Liabilities:	'		'
Senior Notes due 2014	252	[5]	253	[5]
Long-term Debt [Member] | Senior Debt Obligations Due 2014 [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Liabilities:	'		'
Senior Notes due 2014	0	[5]	0	[5]
Money Market Funds [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary assets	14		0
Money Market Funds [Member] | Identical Assets (Level 1) [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary assets	14		0
Money Market Funds [Member] | Observable Inputs (Level 2) [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary assets	0		0
Money Market Funds [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary assets	$0		$0
[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 other receivables in the consolidated balance sheets.
[4]	Included in accounts payable and accrued liabilities and other liabilities in the consolidated balance sheets.
[5]	Included in long-term debt 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) (Contingent Consideration [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Contingent Consideration [Member]	'	'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at January 1,	$104	$63
Additions	55	0
Payments	-30	-3
Revaluation Impact	4	1
Balance at March 31,	$133	$61

Retirement_Benefits_Narrative_

Retirement Benefits (Narrative) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Defined Benefit Plan Disclosure [Line Items]	'	'
Contributions to U.S. non qualified and non-U.S. Pension Plan	$54	'
Non-U.S. Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Effect of plan amendment on accumulated benefit obligation	147	'
Effect of plan amendment on funded status	-137	'
Gain (loss) due to curtailments	65	0
Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Expected contribution during remainder of 2013	130	'
Gain (loss) due to curtailments	$65	$0
Equity Funds [Member] | United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Target asset allocation U.S. Plan, equities, prior period	58.00%	'
Actual asset allocation percentage of equity	62.00%	'
Fixed Income Funds [Member] | United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Target asset allocation U.S. Plan, equities, prior period	42.00%	'
Actual asset allocation percentage of equity	38.00%	'
United Kingdom [Member] | Equity Funds [Member] | Non-U.S. Plans [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Target asset allocation U.S. Plan, equities, prior period	50.00%	'
Actual asset allocation percentage of equity	48.00%	'
United Kingdom [Member] | Fixed Income Funds [Member] | Non-U.S. Plans [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Target asset allocation U.S. Plan, equities, prior period	50.00%	'
Actual asset allocation percentage of equity	52.00%	'
United Kingdom [Member] | Geographic Concentration Risk [Member] | Non-U.S. Plans [Member] | Non-U.S. Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Concentration risk percentage	82.00%	'

Retirement_Benefits_Schedule_O

Retirement Benefits (Schedule Of Defined Benefit Plan Net Periodic Benefit Cost) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Service cost	$61	$64
Interest cost	161	145
Expected return on plan assets	-248	-228
Amortization of prior service credit	-3	-5
Recognized actuarial loss	51	78
Net periodic benefit cost	22	54
Curtailment (credit)	-65	0
Total cost (credit)	-43	54
U.S. Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Service cost	22	27
Interest cost	63	57
Expected return on plan assets	-86	-81
Amortization of prior service credit	-2	-4
Recognized actuarial loss	26	51
Total cost (credit)	23	50
Non-U.S. Pension Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Service cost	39	37
Interest cost	98	88
Expected return on plan assets	-162	-147
Amortization of prior service credit	-1	-1
Recognized actuarial loss	25	27
Net periodic benefit cost	-1	4
Curtailment (credit)	-65	0
Total cost (credit)	-66	4
Postretirement Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Service cost	1	2
Interest cost	3	3
Expected return on plan assets	'	'
Amortization of prior service credit	'	'
Recognized actuarial loss	'	'
Net periodic benefit cost	4	5
Curtailment (credit)	0	0
Total cost (credit)	4	5
U.S. Postretirement Benefits [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Service cost	0	1
Interest cost	2	2
Expected return on plan assets	'	'
Amortization of prior service credit	'	'
Recognized actuarial loss	'	'
Total cost (credit)	2	3
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Service cost	1	1
Interest cost	1	1
Expected return on plan assets	'	'
Amortization of prior service credit	'	'
Recognized actuarial loss	'	'
Net periodic benefit cost	2	2
Total cost (credit)	$2	$2

Retirement_Benefits_Schedule_O1

Retirement Benefits (Schedule Of Defined Benefit Plan Weighted Average Assumption Used In Calculating Net Periodic Benefit Cost) (Details)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Pension Benefits [Member]	'	'
Weighted average assumptions:	'	'
Expected return on plan assets	7.53%	7.66%
Discount rate	4.74%	4.38%
Rate of compensation increase	2.64%	2.43%
Postretirement Benefits [Member]	'	'
Weighted average assumptions:	'	'
Expected return on plan assets	0.00%	0.00%
Discount rate	5.03%	4.32%
Rate of compensation increase	0.00%	0.00%

Debt_Narrative_Details

Debt (Narrative) (Details) (USD $)

1 Months Ended

3 Months Ended

3 Months Ended

0 Months Ended

0 Months Ended

1 Months Ended

1 Months Ended

1 Months Ended

3 Months Ended

Feb. 28, 2011

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2011

Mar. 31, 2014

Mar. 31, 2014

Mar. 31, 2014

Mar. 28, 2014

Mar. 31, 2014

Mar. 28, 2014

Mar. 31, 2014

Dec. 31, 2012

Mar. 31, 2014

Mar. 31, 2014

Feb. 28, 2011

Oct. 31, 2013

Mar. 31, 2014

Feb. 28, 2013

Feb. 28, 2011

Mar. 31, 2014

Mar. 31, 2013

Mar. 31, 2014

interest_rate_swap

interest_rate_swap

Senior Debt Obligations Due 2018 [Member]

Senior Debt Obligations Due 2023 [Member]

Senior Debt Obligations Due 2017 [Member]

Revolving Credit Facility [Member]

Revolving Credit Facility [Member]

Amended Revolving Credit Facility March 28, 2014 [Member]

Amended Revolving Credit Facility March 28, 2014 [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Senior Debt Obligations Due 2014 [Member]

Senior Debt Obligations Due 2014 [Member]

Senior Debt Obligations Due 2015 [Member]

Senior Debt Obligations Due 2015 [Member]

Senior Debt Obligations Due 2013 [Member]

London Interbank Offered Rate (LIBOR) [Member]

Interest Rate Swap [Member]

Interest Rate Swap [Member]

Commercial Paper [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Proceeds from issuance of debt

'

'

'

'

$250,000,000

$250,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate

'

'

'

'

2.55%

4.05%

2.30%

'

'

'

'

'

'

5.38%

5.38%

'

5.75%

4.85%

'

'

'

'

Debt partial redemption amount

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

'

'

'

'

'

Cash outflow on redemption of debt

'

3,000,000

252,000,000

'

'

'

'

'

'

'

'

'

'

'

'

275,000,000

'

'

'

'

'

'

Cost for early redemption

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

24,000,000

'

'

'

'

'

'

Repaid senior notes that matured

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

'

'

'

'

Commercial paper

'

100,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Commercial paper, weighted average interest rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.32%

Term of debt

'

'

'

'

'5 years

'10 years

'

'5 years

'

'5 years

'

'3 years

'

'

'

'

'

'

'

'

'

'

Line of credit facility, current borrowing capacity

'

'

'

'

'

'

'

'

1,000,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

Revolving credit facility, amount outstanding

'

'

'

'

'

'

'

'

'

'

0

'

50,000,000

'

'

'

'

'

'

'

'

'

Debt facilities, maximum borrowing capacity

'

'

'

'

'

'

'

'

'

1,200,000,000

'

50,000,000

'

'

'

'

'

'

'

'

'

'

Interest rate on three-year draw term loan facility

'

'

'

'

'

'

'

'

'

'

'

'

1.28%

'

'

'

'

'

'

'

'

'

Number of interest rate swaps

2

'

'

2

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate swap for hedging

125,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate swap maturity, in years

'3 years 6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.375% senior notes due in 2014, hedged value

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

250,000,000

'

'

'

'

'

'

'

Fixed interest rate of swaps

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.38%

'

'

'

'

'

'

'

Floating rate three-month LIBOR plus fixed spread interest percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.73%

'

'

'

Term of interest rate swap net settlement (in months)

'

'6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate swaps, fair value adjustment

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Swap agreements, effectiveness recognized during the period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$0

$0

'

Debt_Schedule_Of_Outstanding_D

Debt (Schedule Of Outstanding Debt) (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013	Feb. 28, 2011
In Millions, unless otherwise specified
Debt Instrument [Line Items]	'	'	'
Current portion of long-term debt	$332	$334	'
Short-term debt	432	334	'
Long-term debt, current and noncurrent	2,951	2,955	'
Long-term debt and capital lease obligations	2,619	2,621	'
Senior Debt Obligations Due 2033 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	297	297	'
Interest rate	5.88%	'	'
Senior Debt Obligations Due 2014 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	322	323	'
Interest rate	5.38%	'	5.38%
Senior Debt Obligations Due 2015 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	230	230	'
Interest rate	5.75%	'	'
Senior Debt Obligations Due 2017 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	249	249	'
Interest rate	2.30%	'	'
Senior Debt Obligations Due 2019 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	399	399	'
Interest rate	9.25%	'	'
Senior Debt Obligations Due 2021 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	497	497	'
Interest rate	4.80%	'	'
Senior Debt Obligations Due 2018 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	248	248	'
Interest rate	2.55%	'	'
Senior Debt Obligations Due 2023 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	247	247	'
Interest rate	4.05%	'	'
Mortgage Due 2035 [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	410	413	'
Interest rate	5.70%	'	'
Three-Year Delayed Draw Term Loan Facility [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	50	50	'
Other [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Long-term debt, current and noncurrent	2	2	'
Commercial Paper [Member]	'	'	'
Debt Instrument [Line Items]	'	'	'
Commercial paper	$100	$0	'

Debt_Gain_Or_Loss_On_The_Hedge

Debt (Gain Or Loss On The Hedged Item And Offsetting Gain Or Loss On Interest Rate Swaps) (Details) (Other Operating Expenses [Member], USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Mar. 31, 2013
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Gain on Notes	$1	$1
Other operating expenses net income effect	0	0
Interest Rate Swap [Member]	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Loss on Swaps	($1)	($1)

Debt_Estimated_Fair_Value_of_S

Debt Estimated Fair Value of Significant Financial Instruments (Details) (USD $)	Mar. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Carrying Amount [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Short-term debt	$432	$334
Long-term debt	2,619	2,621
Fair Value [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Short-term debt	439	334
Long-term debt	$2,844	$2,819

Restructuring_Costs_Restructur

Restructuring Costs (Restructuring Activities) (Details) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Restructuring Reserve [Roll Forward]	'	'
Liability at beginning of period	$124	$170
Amounts Accrued	2	22
Cash Paid	-15	-65
Other	'	-3
Liability at end of period	111	124
Severance [Member]	'	'
Restructuring Reserve [Roll Forward]	'	'
Liability at beginning of period	11	36
Amounts Accrued	0	9
Cash Paid	-3	-33
Other	'	-1
Liability at end of period	8	11
Future Rent Under Non-Cancelable Leases and Other Costs [Member]	'	'
Restructuring Reserve [Roll Forward]	'	'
Liability at beginning of period	113	134
Amounts Accrued	2	13
Cash Paid	-12	-32
Other	'	-2
Liability at end of period	103	113
Corporate Segment [Member]	'	'
Restructuring Reserve [Roll Forward]	'	'
Amounts Accrued	$2	'

Common_Stock_Details

Common Stock (Details) (USD $)	1 Months Ended	3 Months Ended
Share data in Millions, unless otherwise specified	31-May-13	Mar. 31, 2014	Mar. 31, 2013
Equity, Class of Treasury Stock [Line Items]	'	'	'
Payments for repurchase of common stock	'	$100,000,000	100,000,000
Common Stock [Member]	'	'	'
Equity, Class of Treasury Stock [Line Items]	'	'	'
Common stock repurchased (in shares)	'	2	2.7
Share repurchases program, authorized amount	1,000,000,000	'	'
Stock repurchase program, remaining authorized repurchase amount	'	$463,000,000	'

Claims_Lawsuits_And_Other_Cont1

Claims, Lawsuits And Other Contingencies (Details) (GBP £)	Mar. 31, 2014
In Millions, unless otherwise specified	lawsuit
Governmental Inquiries and Related Claims [Member]	'
Loss Contingencies [Line Items]	'
Number of actions instituted by policyholders	2
Other Contingencies-Guarantees [Member]	'
Loss Contingencies [Line Items]	'
Amount reinsured by third party	40

Segment_Information_Selected_I

Segment Information (Selected Information And Details For MMC's Operating Segments) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Segment Reporting Information [Line Items]	'		'
Revenue	$3,264		$3,126
Operating Income (Loss)	673		607
Risk and Insurance Services Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Interest income on fiduciary funds	6		8
Consulting Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Interest income on fiduciary funds	1		1
Operating Segments [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	3,271		3,133
Operating Income (Loss)	718		655
Operating Segments [Member] | Risk and Insurance Services Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	1,839	[1]	1,771	[1]
Operating Income (Loss)	493		468
Interest income on fiduciary funds	6		8
Equity method income	'		1
Operating Segments [Member] | Consulting Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	1,432	[2]	1,362	[2]
Operating Income (Loss)	225		187
Intersegment Eliminations [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	-7		-7
Intersegment Eliminations [Member] | Consulting Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	7		7
Corporate, Non-Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Operating Income (Loss)	($45)		($48)
[1]	Includes interest income on fiduciary funds of $6 million and $8 million in 2014 and 2013, respectively, and equity method income of $1 million in 2013, respectively.
[2]	Includes inter-segment revenue of $7 million in both 2014 and 2013 and interest income on fiduciary funds of $1 million in both 2014 and 2013.

Segment_Information_Details_of

Segment Information (Details of Operating Segment Revenue) (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014		Mar. 31, 2013
Segment Reporting Information [Line Items]	'		'
Revenue	$3,264		$3,126
Operating Segments [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	3,271		3,133
Operating Segments [Member] | Marsh Insurance Group [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	1,457		1,395
Operating Segments [Member] | Guy Carpenter Reinsurance Group [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	382		376
Operating Segments [Member] | Mercer Consulting Group [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	1,061		1,041
Operating Segments [Member] | Oliver Wyman Group Consulting Group [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	371		321
Operating Segments [Member] | Risk and Insurance Services Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	1,839	[1]	1,771	[1]
Operating Segments [Member] | Consulting Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	1,432	[2]	1,362	[2]
Intersegment Eliminations [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	-7		-7
Intersegment Eliminations [Member] | Consulting Segment [Member]	'		'
Segment Reporting Information [Line Items]	'		'
Revenue	$7		$7
[1]	Includes interest income on fiduciary funds of $6 million and $8 million in 2014 and 2013, respectively, and equity method income of $1 million in 2013, respectively.
[2]	Includes inter-segment revenue of $7 million in both 2014 and 2013 and interest income on fiduciary funds of $1 million in both 2014 and 2013.