Marsh & McLennan Companies (MMC) 10-K 27 Feb 14 2013 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
	Dec. 31, 2013	Feb. 21, 2014	Jun. 30, 2013
Document And Entity Information [Abstract]	'	'	'
Document Type	'10-K	'	'
Amendment Flag	'false	'	'
Document Period End Date	31-Dec-13	'	'
Document Fiscal Year Focus	'2013	'	'
Document Fiscal Period Focus	'FY	'	'
Trading Symbol	'MMC	'	'
Entity Registrant Name	'MARSH & MCLENNAN COMPANIES, INC.	'	'
Entity Central Index Key	'0000062709	'	'
Current Fiscal Year End Date	'--12-31	'	'
Entity Well-known Seasoned Issuer	'Yes	'	'
Entity Voluntary Filers	'No	'	'
Entity Current Reporting Status	'Yes	'	'
Entity Filer Category	'Large Accelerated Filer	'	'
Entity Common Stock, Shares Outstanding	'	548,374,223	'
Entity Public Float	'	'	$21,878,761,313

Consolidated_Statements_Of_Inc

Consolidated Statements Of Income (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]	'	'	'
Revenue	$12,261	$11,924	$11,526
Expense:	'	'	'
Compensation and benefits	7,226	7,134	6,969
Other operating expenses	2,958	2,961	2,919
Operating expenses	10,184	10,095	9,888
Operating income	2,077	1,829	1,638
Interest income	18	24	28
Interest expense	-167	-181	-199
Cost of extinguishment of debt	-24	0	-72
Investment income	69	24	9
Income before income taxes	1,973	1,696	1,404
Income tax expense	594	492	422
Income from continuing operations	1,379	1,204	982
Discontinued operations, net of tax	6	-3	33
Net income before non-controlling interests	1,385	1,201	1,015
Less: Net income attributable to non-controlling interests	28	25	22
Net income attributable to the Company	$1,357	$1,176	$993
Basic net income per share	'	'	'
Continuing operations (in dollars per share)	$2.46	$2.16	$1.76
Net income attributable to the Company (in dollars per share)	$2.47	$2.16	$1.82
Diluted net income per share	'	'	'
Continuing operations (in dollars per share)	$2.42	$2.13	$1.73
Net income attributable to the Company (in dollars per share)	$2.43	$2.13	$1.79
Average number of shares outstanding	'	'	'
Basic (in shares)	549	544	542
Diluted (in shares)	558	552	551
Shares outstanding at December 31 (in shares)	547	545	539

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Net income before non-controlling interests	$1,385	$1,201	$1,015
Other comprehensive income (loss), before tax:	'	'	'
Foreign currency translation adjustments	-86	177	-100
Unrealized investment loss	1	-1	-9
Gain (loss) related to pension/post-retirement plans	1,213	-447	-1,114
Other comprehensive income (loss), before tax	1,128	-271	-1,223
Income tax expense (credit) on other comprehensive loss	442	-152	-335
Other comprehensive income (loss), net of tax	686	-119	-888
Comprehensive income	2,071	1,082	127
Less: Comprehensive income attributable to non-controlling interests	28	25	22
Comprehensive income attributable to the Company	$2,043	$1,057	$105

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Current assets:	'	'
Cash and cash equivalents	$2,303	$2,301
Receivables	'	'
Commissions and fees	3,065	2,858
Advanced premiums and claims	61	62
Other	282	244
Gross receivables	3,408	3,164
Less-allowance for doubtful accounts and cancellations	-98	-106
Net receivables	3,310	3,058
Current deferred tax assets	482	410
Other current assets	205	194
Total current assets	6,300	5,963
Goodwill and intangible assets	7,365	7,261
Fixed assets, net	828	809
Pension related assets	979	260
Deferred tax assets	626	1,223
Other assets	882	772
Total assets	16,980	16,288
Current liabilities:	'	'
Short-term debt	334	260
Accounts payable and accrued liabilities	1,861	1,721
Accrued compensation and employee benefits	1,466	1,473
Accrued income taxes	148	110
Total current liabilities	3,809	3,564
Fiduciary liabilities	4,234	3,992
Less – cash and investments held in a fiduciary capacity	-4,234	-3,992
Fiduciary liabilities, net, noncurrent	0	0
Long-term debt	2,621	2,658
Pension, postretirement and postemployment benefits	1,150	2,094
Liabilities for errors and omissions	373	460
Other liabilities	1,052	906
Commitments and contingencies	0	0
Equity:	'	'
Preferred stock, $1 par value, authorized 6,000,000 shares, none issued	0	0
Common stock, $1 par value, authorized 1,600,000,000 shares, issued 560,641,640 shares at December 31, 2013 and December 31, 2012	561	561
Additional paid-in capital	1,028	1,107
Retained earnings	9,452	8,628
Accumulated other comprehensive loss	-2,621	-3,307
Non-controlling interests	70	64
Stockholders Equity Subtotal Before Treasury Stock	8,490	7,053
Less – treasury shares, at cost, 13,882,204 shares at December 31, 2013 and 15,133,774 shares at December 31, 2012	-515	-447
Total equity	7,975	6,606
Total liabilities and stockholders' equity	$16,980	$16,288

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Statement of Financial Position [Abstract]	'	'
Preferred stock, par value (in dollars per share)	$1	$1
Preferred stock, shares authorized (in shares)	6,000,000	6,000,000
Preferred stock, shares issued (in shares)	0	0
Common stock, par value (in dollars per share)	$1	$1
Common stock, shares authorized (in shares)	1,600,000,000	1,600,000,000
Common stock, shares issued (in shares)	560,641,640	560,641,640
Treasury shares, shares (in shares)	13,882,204	15,133,774

Consolidated_Statements_Of_Cas

Consolidated Statements Of Cash Flows (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Operating cash flows:	'	'	'
Net income before non-controlling interests	$1,385	$1,201	$1,015
Adjustments to reconcile net income to cash provided by operations:	'	'	'
Depreciation and amortization of fixed assets and capitalized software	286	277	267
Amortization of intangible assets	72	72	65
Intangible asset impairment	5	8	0
Adjustments to acquisition related contingent consideration liability	24	-44	0
Cost of early extinguishment of debt	24	0	72
Provision for deferred income taxes	184	96	178
Gain on investments	-69	-24	-8
Loss on disposition of assets	1	23	35
Stock option expense	18	26	21
Changes in assets and liabilities:	'	'	'
Net receivables	-245	-144	143
Other current assets	-70	-37	-225
Other assets	-766	-177	-94
Accounts payable and accrued liabilities	106	-210	108
Accrued compensation and employee benefits	-8	72	107
Accrued income taxes	43	44	1
Other liabilities	383	174	32
Effect of exchange rate changes	-32	-35	-12
Net cash provided by operations	1,341	1,322	1,705
Financing cash flows:	'	'	'
Purchase of treasury shares	-550	-230	-361
Proceeds from debt	547	248	496
Repayments of debt	-260	-259	-11
Payments for early extinguishment of debt	-274	0	-672
Purchase of non-controlling interests	0	0	-21
Shares withheld for taxes on vested units – treasury shares	-79	-97	-93
Issuance of common stock from treasury shares	352	248	162
Payments of contingent consideration for acquisitions	-9	-30	-16
Distributions of non-controlling interests	-28	-16	-11
Dividends paid	-533	-497	-480
Net cash used for financing activities	-834	-633	-1,007
Investing cash flows:	'	'	'
Capital expenditures	-401	-320	-280
Net sales of long-term investments	93	20	62
Proceeds from sales of fixed assets	5	6	3
Dispositions	5	0	0
Acquisitions	-142	-292	-237
Other, net	-6	3	-5
Net cash used for investing activities	-446	-583	-457
Effect of exchange rate changes on cash and cash equivalents	-59	82	-22
Increase in cash and cash equivalents	2	188	219
Cash and cash equivalents at beginning of period	2,301	2,113	1,894
Cash and cash equivalents at end of period	$2,303	$2,301	$2,113

Consolidated_Statements_Of_Equ

Consolidated Statements Of Equity (USD $)	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Gain (Loss) [Member]	Treasury Shares [Member]	Non-Controlling Interests [Member]
In Millions, unless otherwise specified
Beginning balance at Dec. 31, 2010	'	$561	$1,185	$7,436	($2,300)	($514)	$47
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'
Change in accrued stock compensation costs	'	'	-13	'	'	'	'
Issuance of shares under stock compensation plans and employee stock purchase plans and related tax impact	'	'	-14	'	'	280	'
Purchase of subsidiary shares from non-controlling interests	'	'	-2	'	'	'	'
Net income before non-controlling interests	1,015	'	'	993	'	'	22
Dividend equivalents declared - (per share amounts: $0.96 in 2013, $0.90 in 2012, and $0.86 in 2011)	'	'	'	-14	'	'	'
Dividends declared – (per share amounts: $0.96 in 2013, $0.90 in 2012, and $0.86 in 2011)	'	'	'	-466	'	'	'
Other comprehensive income (loss), net of tax	-888	'	'	'	-888	'	'
Issuance of shares for acquisitions	'	'	'	'	'	0	'
Purchase of treasury shares	'	'	'	'	'	-361	'
Distributions	11	'	'	'	'	'	-5
Other changes	'	'	'	'	'	'	-7
Ending balance at Dec. 31, 2011	5,940	561	1,156	7,949	-3,188	-595	57
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'
Change in accrued stock compensation costs	'	'	-16	'	'	'	'
Issuance of shares under stock compensation plans and employee stock purchase plans and related tax impact	'	'	-34	'	'	378	'
Purchase of subsidiary shares from non-controlling interests	'	'	1	'	'	'	'
Net income before non-controlling interests	1,201	'	'	1,176	'	'	25
Dividend equivalents declared - (per share amounts: $0.96 in 2013, $0.90 in 2012, and $0.86 in 2011)	'	'	'	-8	'	'	'
Dividends declared – (per share amounts: $0.96 in 2013, $0.90 in 2012, and $0.86 in 2011)	'	'	'	-489	'	'	'
Other comprehensive income (loss), net of tax	-119	'	'	'	-119	'	'
Issuance of shares for acquisitions	'	'	'	'	'	0	'
Purchase of treasury shares	'	'	'	'	'	-230	'
Distributions	16	'	'	'	'	'	-16
Other changes	'	'	'	'	'	'	-2
Ending balance at Dec. 31, 2012	6,606	561	1,107	8,628	-3,307	-447	64
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'	'	'	'	'
Change in accrued stock compensation costs	'	'	-22	'	'	'	'
Issuance of shares under stock compensation plans and employee stock purchase plans and related tax impact	'	'	-57	'	'	481	'
Purchase of subsidiary shares from non-controlling interests	'	'	0	'	'	'	'
Net income before non-controlling interests	1,385	'	'	1,357	'	'	28
Dividend equivalents declared - (per share amounts: $0.96 in 2013, $0.90 in 2012, and $0.86 in 2011)	'	'	'	-6	'	'	'
Dividends declared – (per share amounts: $0.96 in 2013, $0.90 in 2012, and $0.86 in 2011)	'	'	'	-527	'	'	'
Other comprehensive income (loss), net of tax	686	'	'	'	686	'	'
Issuance of shares for acquisitions	'	'	'	'	'	1	'
Purchase of treasury shares	'	'	'	'	'	-550	'
Distributions	28	'	'	'	'	'	-28
Other changes	'	'	'	'	'	'	6
Ending balance at Dec. 31, 2013	$7,975	$561	$1,028	$9,452	($2,621)	($515)	$70

Consolidated_Statements_Of_Equ1

Consolidated Statements Of Equity (Parenthetical) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Statement of Stockholders' Equity [Abstract]	'	'	'
Dividends equivalents declared per share (in dollars per share)	$0.96	$0.90	$0.86
Dividends declared per share (in dollars per share)	$0.96	$0.90	$0.86

Summary_of_Significant_Account

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Summary of Significant Accounting Policies	'
	Summary of Significant Accounting Policies
	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 4 below.
	Principles of Consolidation:  The accompanying consolidated financial statements include all wholly-owned and majority-owned subsidiaries. All significant inter-company transactions and balances have been eliminated.
	Fiduciary Assets and Liabilities:  In its capacity as an insurance broker or agent, the Company generally 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 $27 million, $39 million and $47 million in 2013, 2012 and 2011, respectively. The Consulting segment recorded fiduciary interest income of $5 million in 2013 and $4 million in both 2012 and 2011. 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 $8.2 billion and $9.1 billion at December 31, 2013 and 2012, respectively. 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 $16 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.
	Revenue:  Risk and Insurance Services revenue includes insurance commissions, fees for services rendered and interest income on certain fiduciary funds. Insurance commissions and fees for risk transfer services generally are recorded as of the effective date of the applicable policies or, in certain cases (primarily in the Company's reinsurance broking operations), as of the effective date or billing date, whichever is later. A reserve for policy cancellation is provided based on historic and current data on cancellations. Fees for non-risk transfer services provided to clients are recognized over the period in which the services are provided, using a proportional performance model. Fees resulting from achievement of certain performance thresholds are recorded when such levels are attained and such fees are not subject to forfeiture.
	Consulting revenue includes fees paid by clients for advice and services and commissions from insurance companies for the placement of individual and group contracts. Fee revenue for engagements where remuneration is based on time plus out-of-pocket expenses is recognized based on the amount of time consulting professionals expend on the engagement. For fixed fee engagements, revenue is recognized using a proportional performance model. Revenue from insurance commissions not subject to a fee arrangement is recorded over the effective period of the applicable policies. Revenue for asset based fees is recognized on an accrual basis by applying the daily/monthly rate as contractually agreed with the client to the applicable net asset value. On a limited number of engagements, performance fees may also be earned for achieving certain prescribed performance criteria. Such fees are recognized when the performance criteria have been achieved and agreed to by the client. Reimbursable expenses incurred by professional staff in the generation of revenue and sub-advisory fees related to investment management are included in revenue and the related expenses are included in other operating expenses.
	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.
	Fixed Assets:  Fixed assets are stated at cost less accumulated depreciation and amortization. Expenditures for improvements are capitalized. Upon sale or retirement, the cost and related accumulated depreciation and amortization are removed from the accounts and any gain or loss is reflected in income. Expenditures for maintenance and repairs are charged to operations as incurred.
	Depreciation of buildings, building improvements, furniture, and equipment is provided on a straight-line basis over the estimated useful lives of these assets. Furniture and equipment is depreciated over periods ranging from three to ten years. Leasehold improvements are amortized on a straight-line basis over the periods covered by the applicable leases or the estimated useful life of the improvement, whichever is less. Buildings are depreciated over periods ranging from thirty to forty years. The Company periodically reviews long-lived assets for impairment whenever events or changes indicate that the carrying value of assets may not be recoverable.
	The components of fixed assets are as follows:
	December 31,
	(In millions of dollars)		2013				2012
	Furniture and equipment		$	1,201			$	1,168
	Land and buildings		408				412
	Leasehold and building improvements		816				811
			2,425				2,391
	Less-accumulated depreciation and amortization		(1,597		)		(1,582		)
			$	828			$	809
	Investments:  The Company holds investments primarily in private companies and certain private equity funds.
	Certain investments, primarily investments in private equity funds, are accounted for under the equity method using a consistently applied three-month lag period adjusted for any known significant changes from the lag period to the reporting date of the Company. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. The Company records in earnings, investment gains/losses for its proportionate share of the change in fair value of the funds, which amounted to gains of $12 million, $33 million and $10 million in 2013, 2012 and 2011, respectively. Investments recorded using the equity method are included in other assets in the consolidated balance sheets.
	As part of the sale of MMC Capital in 2005, the Company retained the right to receive certain performance fees related to the Trident II and Trident III private equity partnerships. The Company recognizes performance fee income when such fees are no longer subject to forfeiture, which may take a number of years to resolve. The Company deferred the recognition of income related to such performance fees of $38 million and $63 million at December 31, 2013 and 2012, respectively, related to Trident III. This income is based on the investment performance over the life of each investment in the private equity fund, and future declines in fund performance from current levels may result in the forfeiture of such revenue. Trident II has now fully harvested all its portfolio investments and final distributions were made to partners during the fourth quarter of 2013. Therefore, the Company no longer holds an investment in Trident II. Approximately $40 million and $15 million of performance fees were recognized in 2013 related to Trident III and Trident II, respectively, and included as part of investment income. The Company received approximately $100 million in cash proceeds related to Trident II partnership distributions in 2013.
	Gains or losses recognized in earnings from the investments, including the performance fees discussed above, are included in investment income in the consolidated statements of income.
	Goodwill and Other Intangible Assets:  Goodwill represents acquisition costs in excess of the fair value of net assets acquired. Goodwill is reviewed at least annually for impairment. The Company performs an annual impairment test for each of its reporting units during the third quarter of each year. When a step 1 test is performed, fair values of the reporting units are estimated using either a market approach or a discounted cash flow model. 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. As discussed in Note 6, the Company may elect to assess qualitative factors to determine if a step 1 assessment is necessary. Other intangible assets, which primarily consist of customer lists, that are not deemed to have an indefinite life are amortized over their estimated lives and reviewed for impairment upon the occurrence of certain triggering events in accordance with applicable accounting literature. The Company had no indefinite lived identified intangible assets at December 31, 2013 or 2012.
	Capitalized Software Costs:  The Company capitalizes certain costs to develop, purchase or modify software for the internal use of the Company. These costs are amortized on a straight-line basis over periods ranging from 3 to 10 years. Costs incurred during the preliminary project stage and post implementation stage, are expensed as incurred. Costs incurred during the application development stage are capitalized. Costs related to updates and enhancements are only capitalized if they will result in additional functionality. Capitalized computer software costs of $399 million and $278 million, net of accumulated amortization of $748 million and $691 million at December 31, 2013 and 2012, respectively, are included in other assets in the consolidated balance sheets.
	Legal and Other Loss Contingencies:  The Company and its subsidiaries are subject to a significant number of claims, lawsuits and proceedings including claims for errors and omissions ("E&O"). GAAP requires that a liability be recorded when a loss is both probable and reasonably estimable. Significant management judgment is required to apply this guidance. The Company utilizes case level reviews by inside and outside counsel, an internal actuarial analysis and other analysis to estimate potential losses. 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. Given the unpredictability of E&O claims and of litigation that could flow from them, it is possible that an adverse outcome in a particular matter could have a material adverse effect on the Company’s businesses, results of operations, financial condition or cash flow in a given quarterly or annual period.
	In addition, to the extent that insurance coverage is available, significant management judgment is required to determine the amount of recoveries that are probable of collection under the Company’s various insurance programs.
	The legal and other contingent liabilities described above are not discounted.
	Income Taxes:  The Company's effective tax rate reflects its income, statutory tax rates and tax planning in the various jurisdictions in which it operates. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions and the ability to realize deferred tax assets.
	The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in a tax return. The evaluation of a tax position is a two-step process. The first step involves recognition. The Company determines whether it is more likely than not that a tax position will be sustained upon tax examination, including resolution of any related appeals or litigation, based on only the technical merits of the position. The technical merits of a tax position derive from both statutory and judicial authority (legislation and statutes, legislative intent, regulations, rulings, and case law) and their applicability to the facts and circumstances of the tax position. If a tax position does not meet the more likely than not recognition threshold, the benefit of that position is not recognized in the financial statements. The second step is measurement. A tax position that meets the more likely than not recognition threshold is measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50 percent likely of being realized upon ultimate resolution with a taxing authority.
	Uncertain tax positions are evaluated based upon the facts and circumstances that exist at each reporting period. Subsequent changes in judgment based upon new information may lead to changes in recognition, de-recognition, and measurement. Adjustments may result, for example, upon resolution of an issue with the taxing authorities, or expiration of a statute of limitations barring an assessment for an issue. The Company recognizes interest and penalties, if any, related to unrecognized tax benefits in income tax expense.
	Tax law requires items be included in the Company's tax returns at different times than the items are reflected in the financial statements. As a result, the annual tax expense reflected in the consolidated statements of income is different than that reported in the income tax returns. Some of these differences are permanent, such as expenses that are not deductible in the returns, and some differences are temporary and reverse over time, such as depreciation expense. Temporary differences create deferred tax assets and liabilities. Deferred tax assets generally represent items that can be used as a tax deduction or credit in tax returns in future years for which benefit has already been recorded in the financial statements. Valuation allowances are established for deferred tax assets when it is estimated that future taxable income will be insufficient to use a deduction or credit in that jurisdiction. Deferred tax liabilities generally represent tax expense recognized in the financial statements for which payment has been deferred, or expense for which a deduction has been taken already in the tax return but the expense has not yet been recognized in the financial statements.
	Derivative Instruments:  All derivatives, whether designated in hedging relationships or not, are recorded on the balance sheet at fair value. If the derivative is designated as a fair value hedge, the changes in the fair value of the derivative and of the hedged item attributable to the hedged risk are recognized in earnings. If the derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in other comprehensive income and are recognized in the income statement when the hedged item affects earnings. Changes in the fair value attributable to the ineffective portion of cash flow hedges are recognized in earnings.
	Concentrations of Credit Risk:  Financial instruments which potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents, commissions and fees receivable and insurance recoverables. The Company maintains a policy providing for the diversification of cash and cash equivalent investments and places its investments in a large number of high quality financial institutions to limit the amount of credit risk exposure. Concentrations of credit risk with respect to receivables are generally limited due to the large number of clients and markets in which the Company does business, as well as the dispersion across many geographic areas.
	Per Share Data: From 2009 through 2012, the Company used the two-class method to compute basic and diluted earnings per share ("EPS"). Under the accounting guidance which applies to the calculation of EPS for share-based payment awards with rights to dividends or dividend equivalents, unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are participating securities and should be included in the computation of basic and dilutive EPS using the two-class method.
	In the first quarter of 2013, the share-based payment awards with non-forfeitable rights to dividends became fully vested. As a result, the Company is no longer required to use the two-class method and in the first quarter of 2013 used the treasury stock method to calculate EPS. There was no difference in the earnings per share calculations when comparing the two-class method to the treasury stock method for the years ended 2012 and 2011. Therefore, the prior period information in the chart below shows the earnings per share calculation using the treasury stock method, consistent with current year presentation.
	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 attributable to common shares 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 attributable to common shares 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
	(In millions, except per share figures)	2013				2012				2011
	Net income from continuing operations	$	1,379			$	1,204			$	982
	Less: Net income attributable to non-controlling interests	28				25				22
		$	1,351			$	1,179			$	960
	Basic weighted average common shares outstanding	549				544				542
	Dilutive effect of potentially issuable common shares	9				8				9
	Diluted weighted average common shares outstanding	558				552				551
	Average stock price used to calculate common stock equivalents	$	40.97			$	33.1			$	29.4
	There were 22.6 million, 32.0 million and 38.9 million stock options outstanding as of December 31, 2013, 2012 and 2011, respectively.
	Estimates:  The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results may vary from those estimates.
	New Accounting Pronouncements:  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 to settle taxes that would result from the disallowance of the tax position or the entity does not intend to use the deferred tax asset for this purpose (provided that the tax law permits a choice), 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 will affect balance sheet classification and footnote disclosure only and is not expected to have a material impact on the Company's financial statements.
	In June 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 15, 2013. Earlier application is prohibited. Adoption of the guidance is not expected to materially affect the Company's financial position, results of operations or cash flows.
	In February 2013, the FASB issued new accounting guidance that adds new disclosure requirements for items reclassified out of accumulated other comprehensive income. The Company implemented this new guidance for the reporting period ended March 31, 2013. Other than enhanced disclosure, the adoption of this new guidance did not have a material effect on the Company's financial statements.
	In the first quarter of 2012, the Company adopted new accounting guidance related to the presentation of Comprehensive Income. The new guidance gives an entity the option to present the total of comprehensive income, the components of net income, and the components of other comprehensive income either in a single continuous statement of comprehensive income or in two separate but consecutive statements. In both choices, an entity is required to present each component of net income along with total net income, each component of other comprehensive income along with a total for other comprehensive income, and a total amount for comprehensive income. The guidance eliminates the option to present the components of other comprehensive income as part of the statement of changes in stockholders’ equity. The guidance did not change the items that must be reported in other comprehensive income or when an item of other comprehensive income must be reclassified to net income. Other than enhanced disclosure, adoption of this new guidance did not have a material effect on the Company's financial statements.
	In January 2012, the Company adopted guidance issued by the FASB on accounting and disclosure requirements related to fair value measurements. The guidance expands the disclosures on Level 3 inputs by requiring quantitative disclosure of the unobservable inputs and assumptions, as well as description of the valuation processes, the sensitivity of the fair value to changes in unobservable inputs and the hierarchy classification, valuation techniques, and inputs for assets and liabilities whose fair value is only disclosed in the footnotes.
	Reclassifications: Certain reclassifications have been made to prior period amounts to conform with current year presentation, in particular with regard to the Per Share Data disclosure in Footnote 1, which is presented using the treasury stock method, since there is no difference in the earnings per share calculation between the treasury stock method and the two-class method for the three years presented.

Supplemental_Disclosures

Supplemental Disclosures	12 Months Ended
	Dec. 31, 2013
Supplemental Cash Flow Information [Abstract]	'
Supplemental Disclosures	'
	Supplemental Disclosures
	The following schedule provides additional information concerning acquisitions, interest and income taxes paid:
	(In millions of dollars)	2013			2012			2011
	Assets acquired, excluding cash	$	217		$	380		$	214
	Released from escrow in 2012	—			(62		)	—
	Liabilities assumed	(53		)	(42		)	(21		)
	Contingent/deferred purchase consideration	(39		)	(46		)	(33		)
	Net cash outflow for current year acquisitions	125			230			160
	Purchase of other intangibles	2			3			4
	Deferred purchase consideration from prior years' acquisitions	15			59			11
	Subtotal	$	142		$	292		$	175
	Cash paid into escrow for future acquisition	—			—			62
	Net cash outflow for acquisitions	$	142		$	292		$	237
	(In millions of dollars)	2013			2012			2011
	Interest paid	$	170		$	183		$	188
	Income taxes paid, net of refunds	$	360		$	350		$	37
	The Company had non-cash issuances of common stock under its share-based payment plan of $150 million, $193 million and $197 million for the years ended December 31, 2013, 2012 and 2011, respectively. The Company recorded stock-based compensation expense related to equity awards of $110 million, $152 million and $165 million for the years ended December 31, 2013, 2012 and 2011, respectively.
	The consolidated statement of cash flows includes the cash flow impact of discontinued operations in each cash flow category, which were insignificant to the overall Company.
	An analysis of the allowance for doubtful accounts is as follows:
	For the Year Ended December 31,
	(In millions of dollars)	2013			2012			2011
	Balance at beginning of year	$	106		$	105		$	114
	Provision charged to operations	16			11			11
	Accounts written-off, net of recoveries	(19		)	(12		)	(21		)
	Effect of exchange rate changes and other	(5		)	2			1
	Balance at end of year	$	98		$	106		$	105

Other_Comprehensive_Income_Los

Other Comprehensive Income (Loss)	12 Months Ended
	Dec. 31, 2013
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 year ended December 31, 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, 2013	$	4			$	(3,451	)		$	140		$	(3,307	)
	Other comprehensive income (loss) before reclassifications	1				574				(84		)	491
	Amounts reclassified from accumulated other comprehensive income	—				195				—			195
	Net current period other comprehensive income (loss)	1				769				(84		)	686
	Balance as of December 31, 2013	$	5			$	(2,682	)		$	56		$	(2,621	)
	The components of other comprehensive income (loss) are as follows:
	For the year ended December 31,	2013
	(In millions of dollars)	Pre-Tax			Tax (Credit)			Net of Tax
	Foreign currency translation adjustments	$	(86	)	$	(2	)	$	(84	)
	Unrealized investment gains (losses)	1			—			1
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains	(22		)	(8		)	(14		)
	Net actuarial losses	317			108			209
	Subtotal	295			100			195
	Net gains arising during period	898			339			559
	Foreign currency translation adjustments	27			8			19
	Other adjustments	(7		)	(3		)	(4		)
	Pension/post-retirement plans gains	1,213			444			769
	Other comprehensive income	$	1,128		$	442		$	686
	For the year ended December 31,	2012
	(In millions of dollars)	Pre-Tax			Tax (Credit)			Net of Tax
	Foreign currency translation adjustments	$	177		$	(5	)	$	182
	Unrealized investment losses	(1		)	1			(2		)
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains	(31		)	(12		)	(19		)
	Net actuarial losses	270			90			180
	Subtotal	239			78			161
	Net loss arising during period	(648		)	(217		)	(431		)
	Foreign currency translation adjustments	(113		)	(26		)	(87		)
	Other adjustments	75			17			58
	Pension/post-retirement plans losses	(447		)	(148		)	(299		)
	Other comprehensive loss	$	(271	)	$	(152	)	$	(119	)
	For the year ended December 31,	2011
	(In millions of dollars)	Pre-Tax			Tax (Credit)			Net of Tax
	Foreign currency translation adjustments	$	(100	)	$	4		$	(104	)
	Unrealized investment losses	(9		)	(4		)	(5		)
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains	(32		)	(13		)	(19		)
	Net actuarial losses	213			68			145
	Subtotal	181			55			126
	Net loss arising during period	(1,289		)	(388		)	(901		)
	Foreign currency translation adjustments	(14		)	(3		)	(11		)
	Other adjustments	8			1			7
	Pension/post-retirement plans losses	(1,114		)	(335		)	(779		)
	Other comprehensive loss	$	(1,223	)	$	(335	)	$	(888	)
	The components of accumulated other comprehensive income (loss) are as follows:
	(In millions of dollars)	December 31, 2013				December 31, 2012
	Foreign currency translation adjustments (net of deferred tax liability of $7 and $9 in 2013 and 2012, respectively)	$	56			$	140
	Net unrealized investment gains (net of deferred tax liability of $2 in 2013 and 2012, respectively)	5				4
	Net charges related to pension / post-retirement plans (net of deferred tax asset of $1,213 and $1,657 in 2013 and 2012, respectively)	(2,682		)		(3,451		)
		$	(2,621	)		$	(3,307	)

Acquisitions

Acquisitions	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Acquisitions	'
	Acquisitions
	The Company’s acquisitions have been accounted for as purchases. Net assets and results of operations are included in the Company’s consolidated financial statements commencing at the respective purchase dates. In connection with acquisitions, the Company records the estimated value of the net tangible assets purchased and the value of the identifiable intangible assets purchased, which typically consist of purchased customer lists, trademarks and non-compete agreements. The valuation of purchased intangible assets involves significant estimates and assumptions. Any change in assumptions could affect the carrying value of such intangible assets.
	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.
	Total purchase consideration for acquisitions made during 2013 was $178 million, which consisted of cash paid of $139 million, deferred purchase and estimated contingent consideration of $39 million. Contingent consideration arrangements are primarily based on EBITDA and revenue targets over two to four years. The fair value of the contingent consideration was based on projected revenue and earnings of the acquired entities. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment when purchase accounting is finalized. During 2013, the Company also paid $15 million of deferred purchase consideration and $17 million of contingent consideration related to acquisitions made in prior years. In addition, the Company paid $2 million to purchase other intangible assets during 2013.
	The following table presents the preliminary allocation of the acquisition cost to the assets acquired and liabilities assumed, based on their fair values:
	(In millions)	2013
	Cash	$	139
	Estimated fair value of deferred/contingent consideration	39
	Total Consideration	$	178
	Allocation of purchase price:
	Cash and cash equivalents	$	14
	Accounts receivable, net	10
	Other current assets	12
	Property, plant, and equipment	3
	Intangible assets (primarily customer lists amortized over 10 years)	77
	Goodwill	113
	Other assets	2
	Total assets acquired	231
	Current liabilities	21
	Other liabilities	32
	Total liabilities assumed	53
	Net assets acquired	$	178
	Prior Year Acquisitions
	During 2012, Marsh completed the following twelve acquisitions:
	•	January - Marsh acquired Alexander Forbes' South African brokerage operations, including Alexander Forbes Risk Services and related ancillary operations and insurance broking operations in Botswana and Namibia to expand Marsh's presence in Africa. Marsh subsequently closed the acquisitions of the Alexander Forbes operations in Uganda, Malawi and Zambia.
	•	March - MMA acquired KSPH, LLC, a middle-market employee benefits agency based in Virginia, and Marsh acquired Cosmos Services (America) Inc., the U.S. insurance brokerage subsidiary of ITOCHU Corp., which specializes in commercial property/casualty, personal lines, and employee benefits brokerage services to U.S. subsidiaries of Japanese companies.
	•	June - MMA acquired Progressive Benefits Solutions, an employee benefits agency based in North Carolina, and Security Insurance Services, Inc., a Wisconsin-based insurance agency which offers property/casualty and employee benefits products and services to individuals and businesses.
	•	August - MMA acquired Rosenfeld-Einstein, a South Carolina-based employee benefits service provider, and Eidson Insurance, a property/casualty and employee benefits services firm located in Florida.
	•	October - MMA acquired Howalt+McDowell, a South Dakota-based agency which offers property casualty, surety, personal protection and employee benefits insurance to individuals and businesses, and The Protector Group Insurance Agency, a Massachusetts-based agency which provides property casualty, employee benefits services, personal insurance and individual financial services.
	•	November - MMA acquired Brower Insurance, an Ohio-based company providing employee benefits, property/casualty and consulting services.
	•	December - MMA acquired McGraw Wentworth, a Michigan-based company providing consulting services to mid-sized organizations, and Liscomb Hood Mason, a Minnesota-based company providing property/casualty and employee benefits products and services.
	The MMA acquisitions were made to expand Marsh's presence in the U.S. middle-market business.
	During 2012, Mercer completed the following three acquisitions:
	•	February - Mercer acquired the remaining 49% of Yokogawa-ORC, a global mobility firm based in Japan, which was previously accounted for under the equity method, and Pensjon & Finans, a leading Norway-based financial investment and pension consulting firm.
	•	March - Mercer acquired REPCA, a France-based broking and advisory firm for employer health and benefits plans.
	Total purchase consideration for acquisitions made during 2012 was $360 million, which consisted of cash paid of $252 million, deferred purchase and estimated contingent consideration of $46 million, and cash held in escrow of $62 million at December 31, 2011 that was released in the first quarter of 2012. Contingent consideration arrangements are primarily based on EBITDA and revenue targets over two to four years. The fair value of the contingent consideration was based on projected revenue and earnings of the acquired entities. Estimated fair values of assets acquired and liabilities assumed are subject to adjustment when purchase accounting is finalized. During 2012, the Company also paid $59 million of deferred purchase consideration and $30 million of contingent consideration related to acquisitions made in prior years. In addition, the Company paid $3 million to purchase other intangible assets during 2012.
	Subsequent Acquisitions
	In January 2014, MMA announced that it had 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 announced that it had reached a definitive agreement to acquire 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, with particular expertise in Scotland’s oil and gas sector as well as financial services, construction, and agriculture. It also has an extensive private client offering, specializing in providing tailored insurance solutions for individuals and families.
	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 2013 and 2012 and for the Barney & Barney acquisition that closed in January 2014. In accordance with accounting guidance related to pro-forma disclosures, the information presented for current year acquisitions and the Barney & Barney acquisition is as if they occurred on January 1, 2012 and reflects acquisitions made in 2012 as if they occurred on January 1, 2011. 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.
		Years Ended December 31,
	(In millions, except per share data)	2013		2012		2011
	Revenue	$	12,424	$	12,202	$	11,778
	Income from continuing operations	$	1,387	$	1,222	$	990
	Net income attributable to the Company	$	1,365	$	1,195	$	1,001
	Basic net income per share:
	– Continuing operations	$	2.48	$	2.2	$	1.78
	– Net income attributable to the Company	$	2.49	$	2.2	$	1.84
	Diluted net income per share:
	– Continuing operations	$	2.44	$	2.16	$	1.75
	– Net income attributable to the Company	$	2.45	$	2.16	$	1.81
	The consolidated statements of income for 2013 include approximately $50 million of revenue and $9 million of net operating income, respectively, related to acquisitions made during 2013.

Discontinued_Operations

Discontinued Operations	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Discontinued Operations	'
	Discontinued Operations
	As part of the disposal transactions for Putnam and Kroll, the Company provided certain indemnities, primarily related to pre-transaction tax uncertainties and legal contingencies. In accordance with applicable accounting guidance, liabilities were established related to these indemnities at the time of the sales and reflected as a reduction of the gain on disposal. Discontinued operations includes charges or credits resulting from the settlement or resolution of the indemnified matters, as well as adjustments to the liabilities related to such matters. Discontinued operations in 2011 includes credits of $50 million from the resolution of certain legal matters and insurance recoveries, as well as the settlement of tax audits and the expiration of the statutes of limitations related to certain of the indemnified matters, primarily with respect to Putnam.
	In the fourth quarter of 2011, management initiated a plan to sell the Marsh BPO business, which was completed in August 2012. Marsh's BPO business, previously part of the Marsh U.S. Consumer business, provided policy, claims, call center and accounting operations on an outsourced basis to life insurance carriers. Marsh invested in a technology platform that was designed to make the Marsh BPO business scalable and more efficient. During 2011, Marsh decided that it would cease investing in the technology platform and instead exit the business via a sale. The Company wrote off capitalized software of $17 million, net of tax, which is included in discontinued operations in 2011.
	Summarized Statements of Income data for discontinued operations is as follows:
	For the Year Ended December 31,
	(In millions of dollars)	2013			2012			2011
	Income (loss) from discontinued operations, net of tax	$	—		$	—		$	(17	)
	Disposals of discontinued operations	(4		)	(2		)	25
	Income tax (credit) expense	(10		)	1			(25		)
	Disposals of discontinued operations, net of tax	6			(3		)	50
	Discontinued operations, net of tax	$	6		$	(3	)	$	33
	Discontinued operations, net of tax per share
	– Basic	$	0.01		$	—		$	0.06
	– Diluted	$	0.01		$	—		$	0.06

Goodwill_And_Other_Intangibles

Goodwill And Other Intangibles	12 Months Ended
	Dec. 31, 2013
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 2013, the Company elected to not use the option to perform a qualitative assessment to determine if a step 1 impairment test was necessary and instead elected to perform a step 1 impairment test. Fair values of the reporting units were estimated using either a market approach or 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 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:
	(In millions of dollars)	2013			2012
	Balance as of January 1, as reported	$	6,792		$	6,562
	Goodwill acquired	113			226
	Other adjustments(a)	(12		)	4
	Balance at December 31,	$	6,893		$	6,792
	(a)	Reflects increases due to the impact of foreign exchange in both years. 2013 also reflects a reduction due to purchase accounting adjustments.
	The goodwill acquired of $113 million in 2013 (approximately $7 million of which is deductible for tax purposes) comprised of $96 million related to the Risk and Insurance Services segment and $17 million related to the Consulting segment.
	Goodwill allocable to the Company’s reportable segments is as follows: Risk and Insurance Services, $4.7 billion and Consulting, $2.2 billion.
	Amortized intangible assets consist primarily of the cost of client lists and trade names acquired. The gross cost and accumulated amortization at December 31, 2013 and 2012 is as follows:
	(In millions of dollars)	2013							2012
		Gross			Accumulated		Net		Gross		Accumulated		Net
		Cost			Amortization		Carrying		Cost		Amortization		Carrying
							Amount						Amount
	Amortized intangibles	$	888		$	416	$	472	$	814	$	345	$	469
	The Company recorded an intangible asset impairment charge of $5 million and $8 million in the third quarter of 2013 and 2012, respectively, in the Risk & Insurance Services segment.
	Aggregate amortization expense for each of the years ended December 31, 2013, 2012 and 2011 was $72 million, $72 million and $65 million, respectively. The estimated future aggregate amortization expense is as follows:
	For the Years Ending December 31,
	(In millions of dollars)
	2014	$	77
	2015	75
	2016	68
	2017	61
	2018	58
	Subsequent years	133
		$	472

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Income Taxes	'
	Income Taxes
	For financial reporting purposes, income before income taxes includes the following components:
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Income before income taxes:
	U.S.	$	407			$	398			$	121
	Other	1,566				1,298				1,283
		$	1,973			$	1,696			$	1,404
	The expense (benefit) for income taxes is comprised of:
	Income taxes:
	Current–
	U.S. Federal	$	102			$	42			$	7
	Other national governments	264				336				289
	U.S. state and local	45				24				24
		411				402				320
	Deferred–
	U.S. Federal	12				(18		)		5
	Other national governments	149				89				90
	U.S. state and local	22				19				7
		183				90				102
	Total income taxes	$	594			$	492			$	422
	The significant components of deferred income tax assets and liabilities and their balance sheet classifications are as follows:
	December 31,
	(In millions of dollars)	2013				2012
	Deferred tax assets:
	Accrued expenses not currently deductible	$	570			$	589
	Differences related to non-U.S. operations (a)	140				159
	Accrued retirement & postretirement benefits—non-U.S. operations	—				107
	Accrued retirement benefits U.S.	297				604
	Net operating losses (b)	79				104
	Income currently recognized for tax	74				75
	Foreign tax credit carryforwards	157				224
	Other	90				77
		$	1,407			$	1,939
	Deferred tax liabilities:
	Unrealized investment holding gains	$	2			$	2
	Differences related to non-U.S. operations	112				107
	Depreciation and amortization	273				245
	Accrued retirement & postretirement benefits - non-U.S. operations	89				—
	Other	3				4
		$	479			$	358
	(a)	Net of valuation allowances of $12 million in 2013 and $7 million in 2012.
	(b)	Net of valuation allowances of $70 million in 2013 and $65 million in 2012.
	December 31,
	(In millions of dollars)	2013				2012
	Balance sheet classifications:
	Current assets	$	482			$	410
	Other assets	$	626			$	1,223
	Current liabilities	$	(18	)		$	(18	)
	Other liabilities	$	(162	)		$	(34	)
	U.S. Federal income taxes are not provided on temporary differences with respect to investments in foreign subsidiaries that are essentially permanent in duration, which at December 31, 2013, the Company estimates, amounted to approximately $5.2 billion. The determination of the unrecognized deferred tax liability with respect to these investments is not practicable.
	A reconciliation from the U.S. Federal statutory income tax rate to the Company’s effective income tax rate is shown below.
	For the Years Ended December 31,	2013			2012			2011
	U.S. Federal statutory rate	35	%		35	%		35	%
	U.S. state and local income taxes—net of U.S. Federal income tax benefit	2.1			1.9			1.6
	Differences related to non-U.S. operations	(6.0	)		(6.1	)		(6.5	)
	Other	(1.0	)		(1.8	)		—
	Effective tax rate	30.1	%		29	%		30.1	%
	The Company’s consolidated tax rate was 30.1%, 29.0% and 30.1% in 2013, 2012 and 2011, respectively. The tax rate in each year reflects foreign operations, which are generally taxed at rates lower than the U.S. statutory tax rate.
	Valuation allowances had net increases of $10 million and $23 million in 2013 and 2012, respectively, and a decrease of $1 million in 2011. During the respective years, adjustments of the beginning of the year balances of valuation allowances decreased income tax expense by $3 million in 2013 and increased income tax expense by $16 million in 2012. None of the cumulative valuation allowances relate to amounts which if realized would increase contributed capital in the future. Approximately 66% of the Company’s net operating loss carryforwards expire from 2014 through 2033, and others are unlimited. The potential tax benefit from net operating loss carryforwards at the end of 2013 comprised state and local, and non-U.S. tax benefits of $60 million and $90 million, respectively, before reduction for valuation allowances. Foreign tax credit carryforwards expire from 2019 through 2022.
	The realization of deferred tax assets depends on generating future taxable income during the periods in which the tax benefits are deductible or creditable. The Company and Marsh have been profitable in the U.S. and globally. Tax liabilities are determined and assessed on a legal entity and jurisdictional basis. Certain taxing authorities allow or require combined or consolidated tax filings. The Company assessed the realizability of its domestic deferred tax assets, particularly state deferred tax assets of Marsh relating to jurisdictions in which it files separate tax returns, state deferred tax assets of all of the Company's domestic operations related to jurisdictions in which the Company files a unitary or combined state tax return, and foreign tax credit carry-forwards in the Company's consolidated U.S. federal tax return. When making its assessment about the realization of its domestic deferred tax assets at December 31, 2013, the Company considered all available evidence, placing particular weight on evidence that could be objectively verified. The evidence considered included (i) the profitability of the Company's U.S. operations throughout the period 2011 to 2013, (ii) the nature, frequency, and severity of losses incurred prior to 2011, (iii) profit trends evidenced by continued improvements in the Company's and Marsh's operating performance, (iv) the non-recurring nature of some of the items that contributed to the losses before 2011, (v) the carry-forward periods for the net operating losses ("NOLs") and foreign tax credit carryforwards, (vi) the sources and timing of future taxable income, giving weight to sources according to the extent to which they can be objectively verified, and (vii) tax planning strategies that would be implemented, if necessary, to accelerate utilization of NOLs. Based on its assessment, the Company concluded that it is more likely than not that most of these deferred tax assets are realizable and a valuation allowance was recorded to reduce the domestic deferred tax assets to the amount that the Company believes is more likely than not to be realized. In the event sufficient taxable income is not generated in future periods, additional valuation allowances of up to approximately $195 million could be required relating to these domestic deferred tax assets. The realization of the remaining U.S. federal deferred tax assets is not as sensitive to U.S. profits because it is supported by anticipated repatriation of future annual earnings from the Company’s profitable global operations, consistent with the Company's historical practice. In addition, when making its assessment about the realization of its domestic deferred tax assets at December 31, 2013, the Company continued to assess the realizability of deferred tax assets of certain other entities with a history of recent losses, including other U.S. entities that file separate state tax returns and foreign subsidiaries, and recorded valuation allowances as appropriate.
	Following is a reconciliation of the Company’s total gross unrecognized tax benefits for the years ended December 31, 2013, 2012 and 2011:
	(In millions of dollars)	2013				2012				2011
Balance at January 1,	$	117			$	143			$	199
Additions, based on tax positions related to current year	16				26				7
Additions for tax positions of prior years	35				35				39
Reductions for tax positions of prior years	(7		)		(41		)		(91		)
Settlements	(3		)		(6		)		(6		)
Lapses in statutes of limitation	(30		)		(40		)		(5		)
Balance at December 31,	$	128			$	117			$	143
Of the total unrecognized tax benefits at December 31, 2013, 2012 and 2011, $71 million, $96 million and $102 million, respectively, represent the amount that, if recognized, would favorably affect the effective tax rate in any future periods. The total gross amount of accrued interest and penalties at December 31, 2013, 2012 and 2011, before any applicable federal benefit, was $10 million, $13 million and $17 million, respectively.
As discussed in Note 5, the Company has provided certain indemnities related to contingent tax liabilities as part of the disposals of Putnam and Kroll. At December 31, 2013, 2012 and 2011, $2 million, $6 million and $14 million, respectively, included in the table above, relates to Putnam and Kroll positions included in consolidated Company tax returns. Since the Company remains primarily liable to the taxing authorities for resolution of uncertain tax positions related to consolidated returns, these balances will remain as part of the Company’s consolidated liability for uncertain tax positions. Any future charges or credits that are directly related to the disposal of Putnam and Kroll and the indemnified contingent tax issues, including interest accrued, will be recorded in discontinued operations as incurred.
The Company is routinely examined by the jurisdictions in which it has significant operations. During 2013, the Company settled federal tax audits with the Internal Revenue Service (IRS) for years 2007 and 2009 through 2011. The tax year 2008 was settled in a prior period. During 2011, the Company was accepted to participate in the IRS Compliance Assurance Process (CAP) which is structured to conduct real-time compliance reviews.  The IRS is currently examining 2012 and performing a pre-filing review of the Company's 2013 U.S. operations. New York State and New York City have examinations underway for various entities covering the years 2007 through 2011. During 2013, the State of Illinois commenced an audit of the Company for years 2009 through 2012. During 2013, the Company filed appeals in the Massachusetts Appellate Tax Board for various entities for assessments received at the end of 2012, and the Company is currently appealing those assessments. During 2013, the United Kingdom commenced an examination of tax years 2011 and 2012 for various subsidiaries. There are no ongoing tax audits in the jurisdictions outside the U.S. in which the Company has significant operations. The Company regularly considers the likelihood of assessments in each of the taxing jurisdictions resulting from examinations. The Company has established appropriate liabilities for uncertain tax positions in relation to the potential assessments. The Company believes the resolution of tax matters will not have a material effect on the consolidated financial position of the Company, although a resolution of tax matters could have a material impact on the Company's net income or cash flows and on its effective tax rate in a particular future period. It is reasonably possible that the total amount of unrecognized tax benefits will decrease between zero and approximately $21 million within the next twelve months due to settlement of audits and expiration of statutes of limitation.

Retirement_Benefits

Retirement Benefits	12 Months Ended
	Dec. 31, 2013
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.
	Combined U.S. and non-U.S. Plans
	The weighted average actuarial assumptions utilized for the U.S. and significant non-U.S. defined benefit plans and postretirement benefit plans are as follows:
		Pension						Postretirement
		Benefits						Benefits
		2013			2012			2013			2012
	Weighted average assumptions:
	Discount rate (for expense)	4.38	%		4.91	%		4.32	%		5.05	%
	Expected return on plan assets	7.68	%		8.03	%		—			—
	Rate of compensation increase (for expense)	2.43	%		3.09	%		—			—
	Discount rate (for benefit obligation)	4.82	%		4.38	%		5.03	%		4.32	%
	Rate of compensation increase (for benefit obligation)	2.64	%		2.43	%		—			—
	The Company uses actuaries from Mercer, a subsidiary of the Company, to perform valuations of its pension plans. The long-term rate of return on plan assets assumption is determined for each plan based on the facts and circumstances that exist as of the measurement date, and the specific portfolio mix of each plan’s assets. The Company utilizes a model developed by the Mercer actuaries to assist in the determination of this assumption. The model takes into account several factors, including: actual and target portfolio allocation; investment, administrative and trading expenses incurred directly by the plan trust; historical portfolio performance; relevant forward-looking economic analysis; and expected returns, variances and correlations for different asset classes. These measures are used to determine probabilities using standard statistical techniques to calculate a range of expected returns on the portfolio. The Company generally does not adjust the rate of return assumption from year to year if, at the measurement date, it is within the best estimate range, defined as between the 25th and 75th percentile of the expected long-term annual returns in accordance with the “American Academy of Actuaries Pension Practice Council Note May 2001 Selecting and Documenting Investment Return Assumptions” and consistent with Actuarial Standards of Practice No. 27. Historical long-term average asset returns of each plan are also reviewed to determine whether they are consistent and reasonable compared with the best estimate range. The expected return on plan assets is determined by applying the assumed long-term rate of return to the market-related value of plan assets. This market-related value recognizes investment gains or losses over a five-year period from the year in which they occur. Investment gains or losses for this purpose are the difference between the expected return calculated using the market-related value of assets and the actual return based on the market value of assets. Since the market-related value of assets recognizes gains or losses over a five-year period, the future market-related value of the assets will be impacted as previously deferred gains or losses are reflected.
	The target asset allocation for the U.S. Plan is 58% equities and equity alternatives and 42% fixed income. At the end of 2013, the actual allocation for the U.S. Plan was 63% equities and equity alternatives and 37% fixed income. The target asset allocation for the U.K. Plans, which comprise approximately 82% of non-U.S. Plan assets, is 50% equities and equity alternatives and 50% fixed income. At the end of 2013, the actual allocation for the U.K. Plans was 49% equities and equity alternatives and 51% 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 uses threshold-based portfolio rebalancing to ensure the actual portfolio remains consistent with target asset allocation ranges.
	The discount rate selected for each U.S. plan is based on a model bond portfolio with coupons and redemptions that closely match the expected liability cash flows from the plan. Discount rates for non-U.S. plans are based on appropriate bond indices such as the Markit iBoxx £ Corporates AA 15+ index in the U.K. Projected compensation increases reflect current expectations as to future levels of inflation.
	The components of the net periodic benefit cost for defined benefit and other postretirement plans are as follows:
	Combined U.S. and significant non-U.S. Plans	Pension											Postretirement
	For the Years Ended December 31,	Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Service cost	$	252			$	240			$	226		$	5		$	5		$	5
	Interest cost	581				596				609			11			13			13
	Expected return on plan assets	(911		)		(905		)		(887		)	—			—			—
	Amortization of prior service credit	(22		)		(19		)		(19		)	—			(14		)	(13		)
	Recognized actuarial loss (credit)	315				270				215			2			—			(4		)
	Net periodic benefit cost	$	215			$	182			$	144		$	18		$	4		$	1
	Plan Assets
	For the U.S. plan, investment allocation decisions are made by a fiduciary committee composed of senior executives appointed by the Company’s Chief Executive Officer. For the non-U.S. plans, investment allocation decisions are made by local fiduciaries, in consultation with the Company for the larger plans. Plan assets are invested in a manner consistent with the fiduciary standards set forth in all relevant laws relating to pensions and trusts in each country. Primary investment objectives are (1) to achieve an investment return that, in combination with current and future contributions, will provide sufficient funds to pay benefits as they become due, and (2) to minimize the risk of large losses. The investment allocations are designed to meet these objectives by broadly diversifying plan assets among numerous asset classes with differing expected returns, volatilities, and correlations.
	The major categories of plan assets include equity securities, equity alternative investments, and fixed income securities. For the U.S. qualified plan, the category ranges are 53-63% for equities and equity alternatives, and 37-47% for fixed income. For the U.K. Plan, the category ranges are 47-53% for equities and equity alternatives, and 47-53% for fixed income. Asset allocation ranges are evaluated generally every three years. Asset allocation is monitored frequently and re-balancing actions are taken as appropriate.
	Plan investments are exposed to stock market, interest rate, and credit risk. Concentrations of these risks are generally limited due to diversification by investment style within each asset class, diversification by investment manager, diversification by industry sectors and issuers, and the dispersion of investments across many geographic areas.
	Unrecognized Actuarial Gains/Losses
	In accordance with applicable accounting guidance, the funded status of the Company's pension plans is recorded in the consolidated balance sheets and provides for a delayed recognition of actuarial gains or losses arising from changes in the projected benefit obligation due to changes in the assumed discount rates, differences between the actual and expected value of plan assets and other assumption changes. The unrecognized pension plan actuarial gains or losses and prior service costs not yet recognized in net periodic pension cost are recognized in Accumulated Other Comprehensive Income ("AOCI"), net of tax. These gains and losses are amortized prospectively out of AOCI over a period that approximates the average remaining service period of active employees, or for plans in which substantially all the participants are inactive, over the remaining life expectancy of the inactive employees.
	U.S. Plans
	The following schedules provide information concerning the Company’s U.S. defined benefit pension plans and postretirement benefit plans:
		U.S. Pension								U.S.  Postretirement
		Benefits								Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	5,197			$	4,533			$	176		$	162
	Service cost	104				93				3			3
	Interest cost	229				230				7			8
	Plan combination	36				—				—			—
	Actuarial (gain) loss	(547		)		522				(15		)	13
	Medicare Part D subsidy	—				—				1			3
	Benefits paid	(192		)		(181		)		(14		)	(13		)
	Benefit obligation, December 31	$	4,827			$	5,197			$	158		$	176
	Change in plan assets:
	Fair value of plan assets at beginning of year	$	3,936			$	3,493			$	—		$	—
	Plan combination	21				—				—			—
	Actual return on plan assets	488				500				—			—
	Employer contributions	26				124				13			10
	Medicare Part D subsidy	—				—				1			3
	Benefits paid	(192		)		(181		)		(14		)	(13		)
	Fair value of plan assets, December 31	$	4,279			$	3,936			$	—		$	—
	Net funded status, December 31	$	(548	)		$	(1,261	)		$	(158	)	$	(176	)
	Amounts recognized in the consolidated balance sheets:
	Current liabilities	$	(24	)		$	(25	)		$	(8	)	$	(9	)
	Noncurrent liabilities	(524		)		(1,236		)		(150		)	(167		)
	Net liability recognized, December 31	$	(548	)		$	(1,261	)		$	(158	)	$	(176	)
	Amounts recognized in other comprehensive income (loss):
	Prior service credit	$	7			$	23			$	—		$	—
	Net actuarial (loss) gain	(974		)		(1,887		)		13			(2		)
	Total recognized accumulated other comprehensive (loss) income, December 31	$	(967	)		$	(1,864	)		$	13		$	(2	)
Cumulative employer contributions in excess (deficient) of net periodic cost	419				603				(171		)	(174		)
Net amount recognized in consolidated balance sheet	$	(548	)		$	(1,261	)		$	(158	)	$	(176	)
Accumulated benefit obligation at December 31	$	4,753			$	5,114			$	—		$	—
	U.S. Pension								U.S.  Postretirement
	Benefits								Benefits
(In millions of dollars)	2013				2012				2013			2012
Reconciliation of prior service credit (charge) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	23			$	39			$	—		$	13
Recognized as component of net periodic benefit credit	(16		)		(16		)		—			(13		)
Prior service credit, December 31	$	7			$	23			$	—		$	—
	U.S. Pension								U.S.  Postretirement
	Benefits								Benefits
(In millions of dollars)	2013				2012				2013			2012
Reconciliation of net actuarial gain (loss) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	(1,887	)		$	(1,695	)		$	(2	)	$	12
Recognized as component of net periodic benefit cost	208				152				—			(1		)
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	541				(522		)		15			(13		)
Asset experience	164				178				—			—
Total gain (loss) recognized as change in plan assets and benefit obligations	705				(344		)		15			(13		)
Net actuarial gain (loss), December 31	$	(974	)		$	(1,887	)		$	13		$	(2	)
For the Years Ended December 31,	U.S. Pension											U.S. Postretirement
	Benefits											Benefits
(In millions of dollars)	2013				2012				2011			2013			2012			2011
Total recognized in net periodic benefit cost and other comprehensive loss (income)	$	(696	)		$	346			$	467		$	(5	)	$	24		$	(9	)
Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:
	U.S. Pension				U.S. Postretirement
	Benefits				Benefits
(In millions of dollars)	2014				2014
Prior service credit	$	(7	)		$	—
Net actuarial loss	105				1
Projected cost	$	98			$	1
The weighted average actuarial assumptions utilized in determining the above amounts for the U.S. defined benefit and other U.S. postretirement plans as of the end of the year are as follows:
	U.S. Pension						U.S. Postretirement Benefits
	Benefits
	2013			2012			2013			2012
Weighted average assumptions:
Discount rate (for expense)	4.45	%		5.15	%		4.25	%		5.1	%
Expected return on plan assets	8.75	%		8.75	%		—			—
Rate of compensation increase (for expense)	2	%		2	%		—			—
Discount rate (for benefit obligation)	5.3	%		4.45	%		5.17	%		4.25	%
Rate of compensation increase (for benefit obligation)	2	%		2	%		—			—
The projected benefit obligation, accumulated benefit obligation and aggregate fair value of plan assets for U.S. pension plans with accumulated benefit obligations in excess of plan assets were $4.8 billion, $4.8 billion and $4.3 billion, respectively, as of December 31, 2013 and $5.2 billion, $5.1 billion and $3.9 billion, respectively, as of December 31, 2012.
The projected benefit obligation and fair value of plan assets for U.S. pension plans with projected benefit obligations in excess of plan assets was $4.8 billion and $4.3 billion, respectively, as of December 31, 2013 and $5.2 billion and $3.9 billion, respectively, as of December 31, 2012.
As of December 31, 2013, the U.S. qualified plan holds 5.4 million shares of the Company’s common stock which were contributed to the Plan by the Company in 2005. This represented approximately 6% of that plan’s assets as of December 31, 2013. In addition, plan assets may be invested in funds managed by Mercer Investments, a subsidiary of the Company.
The components of the net periodic benefit cost for the U.S. defined benefit and other postretirement benefit plans are as follows:
U.S. Plans only	Pension											Postretirement
For the Years Ended December 31,	Benefits											Benefits
(In millions of dollars)	2013				2012				2011			2013			2012			2011
Service cost	$	104			$	93			$	83		$	3		$	3		$	3
Interest cost	229				230				231			7			8			8
Expected return on plan assets	(324		)		(322		)		(315		)	—			—			—
Amortization of prior service credit	(16		)		(16		)		(16		)	—			(13		)	(13		)
Recognized actuarial loss (credit)	207				152				100			—			(1		)	(4		)
Net periodic benefit cost (credit)	$	200			$	137			$	83		$	10		$	(3	)	$	(6	)
In December 2003, the Medicare Prescription Drug, Improvement and Modernization Act of 2003 became law. The net periodic benefit cost for all periods shown above includes the subsidy.
The assumed health care cost trend rate for Medicare eligibles is approximately 7.6% in 2013, gradually declining to 4.5% in 2028, and the rate for non-Medicare eligibles is 7.5% in 2013, gradually declining to 4.5% in 2028. Assumed health care cost trend rates have a small effect on the amounts reported for the U.S. health care plans because the Company caps its share of health care trend at 5%. A one percentage point change in assumed health care cost trend rates would have the following effects:
(In millions of dollars)	1 Percentage				1 Percentage
	Point Increase				Point Decrease
Effect on total of service and interest cost components	$	—			$	—
Effect on postretirement benefit obligation	$	2			$	(7	)
Estimated Future Contributions
The Company expects to fund approximately $24 million for its U.S. non-qualified plans in 2014. 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 in the U.S. and applicable foreign law. The Company expects less than $1 million of contributions will be required for its U.S. tax-qualified plan through the end of 2014.
Non-U.S. Plans
The following schedules provide information concerning the Company’s non-U.S. defined benefit pension plans and non-U.S. postretirement benefit plans:
	Non-U.S. Pension								Non-U.S.
	Benefits								Postretirement Benefits
(In millions of dollars)	2013				2012				2013			2012
Change in benefit obligation:
Benefit obligation at beginning of year	$	8,579			$	7,717			$	107		$	91
Service cost	148				147				2			2
Interest cost	352				366				4			5
Employee contributions	11				11				—			—
Actuarial (gain) loss	(53		)		419				(8		)	10
Plan amendments	—				(71		)		—			—
Effect of settlement	(2		)		(11		)		—			—
Effect of curtailment	—				(3		)		—			(1		)
Benefits paid	(293		)		(278		)		(4		)	(4		)
Foreign currency changes	(31		)		280				(4		)	4
Other	—				2				—			—
Benefit obligation December 31	$	8,711			$	8,579			$	97		$	107
Change in plan assets:
Fair value of plan assets at beginning of year	$	8,312			$	7,206			$	—		$	—
Actual return on plan assets	698				721				—			—
Effect of settlement	(2		)		(11		)		—			—
Company contributions	620				389				4			4
Employee contributions	11				11				—			—
Benefits paid	(293		)		(278		)		(4		)	(4		)
Foreign currency changes	5				273				—			—
Other	—				1				—			—
Fair value of plan assets, December 31	$	9,351			$	8,312			$	—		$	—
Net funded status, December 31	$	640			$	(267	)		$	(97	)	$	(107	)
Amounts recognized in the consolidated balance sheets:
Non-current assets	$	977			$	258			$	—		$	—
Current liabilities	(5		)		(6		)		(4		)	(4		)
Non-current liabilities	(332		)		(519		)		(93		)	(103		)
Net asset (liability) recognized, December 31	$	640			$	(267	)		$	(97	)	$	(107	)
Amounts recognized in other comprehensive income (loss):
Prior service credit	$	85			$	93			$	—		$	—
Net actuarial (loss) gain	(3,010		)		(3,309		)		(16		)	(27		)
Total recognized accumulated other comprehensive (loss) income, December 31	$	(2,925	)		$	(3,216	)		$	(16	)	$	(27	)
Cumulative employer contributions in excess (deficient) of net periodic cost	3,565				2,949				(81		)	(80		)
Net asset (liability) recognized in consolidated balance sheet, December 31	$	640			$	(267	)		$	(97	)	$	(107	)
Accumulated benefit obligation, December 31	$	8,413			$	8,229			$	—		$	—
	Non-U.S. Pension								Non-U.S.
	Benefits								Postretirement Benefits
(In millions of dollars)	2013				2012				2013			2012
Reconciliation of prior service credit (cost):
Beginning balance	$	93			$	23			$	—		$	1
Recognized as component of net periodic benefit credit	(6		)		(3		)		—			(1		)
Effect of curtailment	—				(1		)		—			—
Changes in plan assets and benefit obligations recognized in other comprehensive income:
Plan amendments	—				71				—			—
Exchange rate adjustments	(2		)		3				—			—
Prior service credit, December 31	$	85			$	93			$	—		$	—
	Non-U.S. Pension								Non-U.S.
	Benefits								Postretirement Benefits
(In millions of dollars)	2013				2012				2013			2012
Reconciliation of net actuarial gain (loss):
Beginning balance	$	(3,309	)		$	(3,038	)		$	(27	)	$	(19	)
Recognized as component of net periodic benefit cost	108				118				2			1
Effect of settlement	—				1				—			—
Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
Liability experience	53				(419		)		8			(10		)
Asset experience	111				138				—			—
Effect of curtailment	—				3				—			1
Total amount recognized as change in plan assets and benefit obligations	164				(278		)		8			(9		)
Exchange rate adjustments	27				(112		)		1			—
Net actuarial gain (loss), December 31	$	(3,010	)		$	(3,309	)		$	(16	)	$	(27	)
For the Years Ended December 31,	Non-U.S. Pension											Non-U.S. Postretirement
	Benefits											Benefits
(In millions of dollars)	2013				2012				2011			2013			2012			2011
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$	(276	)		$	246			$	792		$	(2	)	$	16		$	12
Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:
	Non-U.S. Pension				Non-U.S.
	Benefits				Postretirement Benefits
(In millions of dollars)	2014				2014
Prior service credit	$	(6	)		$	—
Net actuarial loss	95				1
Projected cost	$	89			$	1
The weighted average actuarial assumptions utilized for the non-U.S. defined and postretirement benefit plans as of the end of the year are as follows:
	Non-U.S. Pension						Non-U.S.
	Benefits						Postretirement Benefits
	2013			2012			2013			2012
Weighted average assumptions:
Discount rate (for expense)	4.33	%		4.77	%		4.45	%		4.95	%
Expected return on plan assets	7.17	%		7.68	%		—			—
Rate of compensation increase (for expense)	2.69	%		3.73	%		—			—
Discount rate (for benefit obligation)	4.55	%		4.33	%		4.8	%		4.45	%
Rate of compensation increase (for benefit obligation)	2.99	%		2.69	%		—			—
The non-U.S. defined benefit plans do not have any direct ownership of the Company’s common stock.
The pension plan in the United Kingdom holds a limited partnership interest in the Trident III private equity fund valued at approximately $111 million at December 31, 2013.
The projected benefit obligation, accumulated benefit obligation and fair value of plan assets for the non-U.S. pension plans with accumulated benefit obligations in excess of plan assets were $1.7 billion, $1.5 billion and $1.3 billion, respectively, as of December 31, 2013 and $1.7 billion, $1.6 billion and $1.2 billion, respectively, as of December 31, 2012.
The projected benefit obligation and fair value of plan assets for non-U.S. pension plans with projected benefit obligations in excess of plan assets was $1.7 billion and $1.3 billion, respectively, as of December 31, 2013 and $1.7 billion and $1.2 billion, respectively, as of December 31, 2012.
Subsequent Event
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. 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 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 will be the weighted average resulting from the December 31, 2013 measurement and the January 2014 re-measurement. The Company will recognize a curtailment gain of $63 million in the first quarter of 2014, primarily resulting from the recognition of the remaining prior service credit related to a plan amendment made in December 2012.This will be mostly offset by a transition benefit to certain employees most impacted by the amendment.
Components of Net Periodic Benefits Costs
The components of the net periodic benefit cost for the non-U.S. defined benefit and other postretirement benefit plans and the curtailment, settlement and termination expenses are as follows:
For the Years Ended December 31,	Non-U.S. Pension											Non-U.S. Postretirement
	Benefits											Benefits
(In millions of dollars)	2013				2012				2011			2013			2012			2011
Service cost	$	148			$	147			$	143		$	2		$	2		$	2
Interest cost	352				366				378			4			5			5
Expected return on plan assets	(587		)		(583		)		(572		)	—			—			—
Amortization of prior service cost	(6		)		(3		)		(3		)	—			(1		)	—
Recognized actuarial loss	108				118				115			2			1			—
Net periodic benefit cost	15				45				61			8			7			7
Settlement loss	—				1				—			—			—			—
Curtailment credit	—				(1		)		—			—			—			—
Special termination benefits	—				—				—			—			—			—
Total cost	$	15			$	45			$	61		$	8		$	7		$	7
The assumed health care cost trend rate was approximately 5.80% in 2013, gradually declining to 4.85% in 2031. Assumed health care cost trend rates can have a significant effect on the amounts reported for the non-U.S. health care plans. A one percentage point change in assumed health care cost trend rates would have the following effects:
(In millions of dollars)	1 Percentage				1 Percentage
	Point Increase				Point Decrease
Effect on total of service and interest cost components	$	1			$	(1	)
Effect on postretirement benefit obligation	$	10			$	(8	)
Estimated Future Contributions
The Company expects to fund approximately $160 million to its non-U.S. pension plans in 2014. Funding requirements for non-U.S. plans vary by country. Contribution rates are generally based on local funding practices and requirements, which may differ significantly from measurements under U.S. GAAP. Funding amounts may be influenced by future asset performance, the level of discount rates and other variables impacting the assets and/or liabilities of the plan. Discretionary contributions may also be affected by alternative uses of the Company’s cash flows, including dividends, investments and share repurchases.
Estimated Future Benefit Payments
The Plans' estimated future benefit payments for its pension and postretirement benefits (without reduction for Medicare subsidy receipts) are as follows:
For the Years Ended December 31,	Pension								Postretirement
	Benefits								Benefits
(In millions of dollars)	U.S.				Non-U.S.				U.S.			Non-U.S.
2014	$	207			$	287			$	11		$	4
2015	$	219			$	299			$	11		$	4
2016	$	233			$	318			$	11		$	5
2017	$	244			$	342			$	11		$	5
2018	$	255			$	350			$	11		$	5
2019-2023	$	1,424			$	2,046			$	57		$	27
Defined Benefit Plans Fair Value Disclosures
In December 2008, the FASB issued guidance for Employers’ Disclosures About Pension and Other Post Retirement Benefit Plan Assets. The guidance requires fair value plan asset disclosures for an employer’s defined benefit pension and postretirement plans similar to the guidance on Fair Value Measurements as well as (a) how investment allocation decisions are made, (b) the major categories of plan assets, and (c) significant concentrations of risk within plan assets.
The U.S. and non-U.S. plan investments are classified into Level 1, which refers to investments valued using quoted prices from active markets for identical assets; Level 2, which refers to investments not traded on an active market but for which observable market inputs are readily available; and Level 3, which refers to investments valued based on significant unobservable inputs. Assets and liabilities are classified in their entirety based on the lowest level of input that is significant to the fair value measurement.
The following table sets forth, by level within the fair value hierarchy, a summary of the U.S. and non-U.S. plans investments measured at fair value on a recurring basis at December 31, 2013 and 2012.
	Fair Value Measurements at December 31, 2013
Assets (In millions of dollars)	Quoted Prices in				Significant				Significant			Total
	Active Markets				Other				Unobservable
	for Identical				Observable				Inputs
	Assets				Inputs				(Level 3)
	(Level 1)				(Level 2)
Common/Collective trusts	$	138			$	5,649			$	151		$	5,938
Corporate obligations	—				2,330				4			2,334
Corporate stocks	2,434				5				1			2,440
Private equity/partnerships	—				2				799			801
Government securities	10				340				2			352
Real estate	—				7				312			319
Short-term investment funds	824				15				—			839
Company common stock	261				—				—			261
Other investments	35				3				238			276
Insurance group annuity contracts	—				—				—			—
Swaps	—				2				—			2
Total investments	$	3,702			$	8,353			$	1,507		$	13,562
	Fair Value Measurements at December 31, 2012
Assets (In millions of dollars)	Quoted Prices in				Significant				Significant			Total
	Active Markets				Other				Unobservable
	for Identical				Observable				Inputs
	Assets				Inputs				(Level 3)
	(Level 1)				(Level 2)
Common/Collective trusts	$	16			$	5,376			$	—		$	5,392
Corporate obligations	—				2,236				1			2,237
Corporate stocks	2,005				4				9			2,018
Private equity/partnerships	2				2				824			828
Government securities	9				309				—			318
Real estate	11				8				357			376
Short-term investment funds	410				4				—			414
Company common stock	276				—				—			276
Other investments	11				112				216			339
Insurance group annuity contracts	—				—				23			23
Swaps	—				4				—			4
Total investments	$	2,740			$	8,055			$	1,430		$	12,225
There were no transfers between Level 1 and Level 2 assets during 2013 or 2012.
The tables below set forth a summary of changes in the fair value of the plans’ Level 3 assets for the years ended December 31, 2013 and December 31, 2012:
Assets (In millions)	Fair Value,				Purchases				Sales			Unrealized			Realized			Exchange			Transfers			Fair
	1-Jan-13											Gain/			Gain/			Rate			in/(out)			Value, December 31, 2013
												(Loss)			(Loss)			Impact			and
																					Other
Private equity/Partnerships	$	824			$	146			$	(174	)	$	(155	)	$	150		$	(1	)	$	9		$	799
Real estate	357				21				(95		)	6			26			(3		)	—			312
Other investments	216				18				(13		)	11			—			6			—			238
Common/Collective Trusts	—				61				—			(4		)	—			(5		)	99			151
Insurance group annuity contracts	23				—				—			(1		)	—			—			(22		)	—
Corporate stocks	9				—				—			—			—			—			(8		)	1
Corporate obligations	1				1				—			—			—			—			2			4
Government Securities	—				—				—			(1		)	—			—			3			2
Total assets	$	1,430			$	247			$	(282	)	$	(144	)	$	176		$	(3	)	$	83		$	1,507
Assets (In millions)	Fair Value,				Purchases				Sales			Unrealized			Realized			Exchange			Transfers			Fair
	1-Jan-12											Gain/			Gain/			Rate			in/(out)			Value,
												(Loss)			(Loss)			Impact			and			31-Dec-12
																					Other
Private equity/Partnerships	$	779			$	86			$	(79	)	$	138		$	(113	)	$	13		$	—		$	824
Real estate	319				11				(3		)	104			(86		)	12			—			357
Other investments	202				17				(24		)	11			6			4			—			216
Insurance group annuity contracts	20				160				(157		)	1			(1		)	—			—			23
Corporate stocks	8				1				—			—			—			—			—			9
Corporate obligations	1				—				—			—			—			—			—			1
Total assets	$	1,329			$	275			$	(263	)	$	254		$	(194	)	$	29		$	—		$	1,430
The following is a description of the valuation methodologies used for assets measured at fair value:
Company common stock:  Valued at the closing price reported on the New York Stock Exchange.
Common stocks, preferred stocks, convertible equity securities and rights/warrants (included in Corporate stocks):  Valued at the closing price reported on the primary exchange.
Corporate bonds (included in Corporate obligations):  The fair value of corporate bonds is estimated using recently executed transactions, market price quotations (where observable) and bond spreads. The spread data used are for the same maturity as the bond. If the spread data does not reference the issuer, then data that references a comparable issuer are used. When observable price quotations are not available, fair value is determined based on cash flow models.
Commercial paper (included in Corporate obligations):  The fair value of commercial paper is estimated using observable market data such as maturity date, issue date, credit rating, current commercial paper rates and settlement date.
Commercial mortgage-backed and asset-backed securities (included in Corporate obligations):  Fair value is determined using discounted cash flow models. Observable inputs are based on trade and quote activity of bonds with similar features including issuer vintage, purpose of underlying loan (first or second lien), prepayment speeds and credit ratings. The discount rate is the combination of the appropriate rate from the benchmark yield curve and the discount margin based on quoted prices.
Common/Collective trusts:  Valued at the quoted market prices of the investments at year end.
U.S. government bonds (included in Government securities):  The fair value of U.S. government bonds is estimated by pricing models that utilize observable market data including quotes, spreads and data points for yield curves.
U.S. agency securities (included in Government securities):  U.S. agency securities are comprised of two main categories consisting of agency issued debt and mortgage pass-throughs. Agency issued debt securities are valued by benchmarking market-derived prices to quoted market prices and trade data for identical or comparable securities. Mortgage pass-throughs include certain “To-be-announced” (TBA) securities and mortgage pass-through pools. TBA securities are generally valued using quoted market prices or are benchmarked thereto. Fair value of mortgage pass-through pools are model driven with respect to spreads of the comparable TBA security.
Private equity and real estate partnerships:  Investments in private equity and real estate partnerships are valued based on the fair value reported by the manager of the corresponding partnership. The managers provide unaudited quarterly financial statements and audited annual financial statements which set forth the value of the fund. The valuations obtained from the managers are based on various analyses on the underlying holdings in each partnership, including financial valuation models and projections, comparable valuations from the public markets, and precedent private market transactions. Investments are valued in the accompanying financial statements based on the Plan’s beneficial interest in the underlying net assets of the partnership as determined by the partnership agreement.
Insurance group annuity contracts:  The fair values for these investments are based on the current market value of the aggregate accumulated contributions plus interest earned.
Swap assets and liabilities:  Fair values for interest rate swaps, equity index swaps and inflation swaps are estimated using a discounted cash flow pricing model. These models use observable market data such as contractual fixed rate, broker quotes, spot equity price or index value and dividend data. The fair values of credit default swaps are estimated using an income approach model which determines expected cash flows based on default probabilities from the issuer-specific credit spread curve and credit loss recovery rates, both of which are dependent on market quotes.
Real estate investment trusts:  Valued at the closing price reported on an exchange.
Short-term investment funds:  Primarily high-grade money market instruments valued at net asset value at year-end.
Real estate: Valued by investment managers generally using proprietary pricing models.
Registered investment companies:  Valued at the closing price reported on the primary exchange.
Defined Contribution Plans
The Company maintains certain defined contribution plans for its employees, including the Marsh & McLennan Companies 401(k) Savings & Investment Plan (“401(k) Plan”), that are qualified under U.S. tax laws. Under these plans, eligible employees may contribute a percentage of their base salary, subject to certain limitations. For the 401(k) Plan, the Company matches a fixed portion of the employees’ contributions. The 401(k) Plan contains an Employee Stock Ownership Plan feature under U.S. tax law. Approximately $453 million of the 401(k) Plan’s assets at December 31, 2013 and $375 million at December 31, 2012 were invested in the Company’s common stock. If a participant does not choose an investment direction for his or her future contributions, they are automatically invested in a BlackRock LifePath Portfolio that most closely matches the participant’s expected retirement year. The cost of these defined contribution plans related to continuing operations was $50 million in 2013, $50 million in 2012 and $48 million in 2011. In addition, the Company has a significant defined contribution plan in the U.K. The cost of the U.K. defined contribution plan was $23 million, $ 21 million and $20 million in 2013, 2012 and 2011, respectively. As noted above, effective August 1, 2014, a newly formed defined contribution plan will replace the existing defined contribution and defined benefit plans with regard to future service.

Stock_Benefit_Plans

Stock Benefit Plans	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Stock Benefit Plans	'
	Stock Benefit Plans
	The Company maintains multiple stock-based payment arrangements under which employees are awarded grants of restricted stock units, stock options and other forms of stock-based payment arrangements.
	Marsh & McLennan Companies, Inc. Incentive and Stock Award Plans
	On May 19, 2011, the Marsh & McLennan Companies, Inc. 2011 Incentive and Stock Award Plan (the “2011 Plan”) was approved by the Company's stockholders. The 2011 Plan replaced the Company's two previous equity incentive plans (the 2000 Senior Executive Incentive and Stock Award Plan and the 2000 Employee Incentive and Stock Award Plan).
	The types of awards permitted under the 2011 Plan include stock options, restricted stock and restricted stock units payable in Company common stock or cash, and other stock-based and performance-based awards. The Compensation Committee of the Board of Directors (the “Compensation Committee”) determines, at its discretion, which affiliates may participate in the 2011 Plan, which eligible employees will receive awards, the types of awards to be received, and the terms and conditions thereof. The right of an employee to receive an award may be subject to performance conditions as specified by the Compensation Committee. The 2011 Plan contains provisions which, in the event of a change in control of the Company, may accelerate the vesting of the awards. The 2011 Plan retains the remaining share authority of the two previous plans as of the date the 2011 Plan was approved by stockholders. Awards relating to not more than approximately 23.2 million shares of common stock, plus shares remaining unused under certain pre-existing plans, may be made over the life of the 2011 Plan.
	Our current practice is to grant non-qualified stock options, restricted stock units and/or performance stock units on an annual basis to senior executives and a limited number of other employees as part of their total compensation. We also grant restricted stock units during the year to new hires or as retention awards for certain employees. We have not granted restricted stock since 2005.
	Stock Options: Options granted under the 2011 Plan may be designated as either incentive stock options or non-qualified stock options. The Compensation Committee determines the terms and conditions of the option, including the time or times at which an option may be exercised, the methods by which such exercise price may be paid, and the form of such payment. Options are generally granted with an exercise price equal to the market value of the Company's common stock on the date of grant. These option awards generally vest 25% per annum and have a contractual term of 10 years. Certain stock options granted under the previous equity incentive plans provided for a market-based triggering event before a vested option can be exercised. The terms and conditions of these stock option awards provided that (i) options will vest at a rate of 25% a year beginning one year from the date of grant and (ii) each vested tranche will only become exercisable if the market price of the Company stock appreciates to a level of 15% above the exercise price of the option and maintains that level for at least ten (10) consecutive trading days after the award has vested. The Company accounts for these awards as market-condition options. The effect of the market condition is reflected in the grant-date fair value of such awards. Compensation cost is recognized over the requisite service period and is not subsequently adjusted if the market condition is not met. For awards without a market-based triggering event, compensation cost is generally recognized on a straight-line basis over the requisite service period which is normally the vesting period.
	The estimated fair value of options granted without a market-based triggering event is calculated using the Black-Scholes option pricing valuation model. This model takes into account several factors and assumptions. The risk-free interest rate is based on the yield on U.S. Treasury zero-coupon issues with a remaining term equal to the expected life assumption at the time of grant. The expected life (estimated period of time outstanding) is estimated using the contractual term of the option and the effects of employees' expected exercise and post-vesting employment termination behavior. The Company uses a blended volatility rate based on the following: (i) volatility derived from daily closing price observations for the 10-year period ended on the valuation date, (ii) implied volatility derived from traded options for the period one week before the valuation date and (iii) average volatility for the 10-year periods ended on 15 anniversaries prior to the valuation date, using daily closing price observations. The expected dividend yield is based on expected dividends for the expected term of the stock options.
	The assumptions used in the Black-Scholes option pricing valuation model for options granted by the Company in 2013, 2012 and 2011 are as follows:
		2013		2012		2011
	Risk-free interest rate	1.03%-1.30%		1.26%-1.27%		2.28%-2.90%
	Expected life (in years)	6		6.5		6.75
	Expected volatility	23.6%-24.1%		26.2%-26.4%		25.4%-25.8%
	Expected dividend yield	2.48%-2.54%		2.76%-2.80%		2.75%-2.86%
	The estimated fair value of options granted with a market-based triggering event is calculated using a binomial valuation model. The factors and assumptions used in this model are similar to those utilized in the Black-Scholes option pricing valuation model except that the risk-free interest rate is based on the U.S. Treasury zero-coupon yield curve over the contractual term of the option, and the expected life is calculated by the model. Since 2009, there have been no options granted with a market-based triggering event. All such market-condition options have met their market price targets.
	A summary of the status of the Company’s stock option awards as of December 31, 2013 and changes during the year then ended is presented below:
		Shares			Weighted			Weighted		Aggregate
					Average Exercise			Average		Intrinsic Value
					Price			Remaining		$0
								Contractual
								Term
	Balance at January 1, 2013	32,045,793			$	29.1
	Granted	2,563,951			$	36.55
	Exercised	(9,928,320	)		$	28.31
	Forfeited	(124,911	)		$	30.18
	Expired	(1,988,647	)		$	40.46
	Balance at December 31, 2013	22,567,866			$	29.29		4.9 years		$	428,167
	Options vested or expected to vest at December 31, 2013	22,098,993			$	29.26		4.9 years		$	419,912
	Options exercisable at December 31, 2013	15,750,814			$	28.02		3.6 years		$	318,923
	In the above table, forfeited options are unvested options whose requisite service period has not been met. Expired options are vested options that were not exercised. The weighted-average grant-date fair value of the Company's option awards granted during the years ended December 31, 2013, 2012 and 2011 was $6.21, $6.04 and $6.67, respectively. The total intrinsic value of options exercised during the same periods was $198.1 million, $57.7 million and $23.6 million, respectively.
	As of December 31, 2013, there was $17 million of unrecognized compensation cost related to the Company's option awards. The weighted-average period over which that cost is expected to be recognized is approximately 1.2 years. Cash received from the exercise of stock options for the years ended December 31, 2013, 2012 and 2011 was $281.1 million, $179.3 million and $111.7 million, respectively.
	The Company's policy is to issue treasury shares upon option exercises or share unit conversion. The
	Company intends to issue treasury shares as long as an adequate number of those shares is available.
	Restricted Stock Units and Performance Stock Units: Restricted stock units may be awarded under the Company's 2011 Incentive and Stock Award Plan. The Compensation Committee determines the restrictions on such units, when the restrictions lapse, when the units vest and are paid, and under what terms the units are forfeited. The cost of these awards is amortized over the vesting period, which is generally three years. Awards to senior executives and other employees may include three-year performance-based restricted stock units and three-year service-based restricted stock units. The payout of performance-based restricted stock units (payable in shares of the Company's common stock) may range, generally, from 0-200% of the number of units granted, based on the achievement of objective, pre-determined Company or operating company performance measures, generally, over a three-year performance period. The Company accounts for these awards as performance condition restricted stock units. The performance condition is not considered in the determination of grant date fair value of such awards. Compensation cost is recognized over the performance period based on management's estimate of the number of units expected to vest and is adjusted to reflect the actual number of shares paid out at the end of the three-year performance period. Dividend equivalents are not paid out unless and until such time that the award vests.
	A summary of the status of the Company's restricted stock units and performance stock units as of December 31, 2013 and changes during the period then ended is presented below:
		Restricted Stock Units					Performance Stock Units
		Shares		Weighted Average			Shares		Weighted Average Grant Date Fair Value
				Grant Date
				Fair Value
	Non-vested balance at January 1, 2013	8,964,238		$	28.58		730,838		$	31.32
	Granted	842,433		$	36.7		289,200		$	36.54
	Vested	(5,310,027	)	$	26.96		(76,844	)	$	31.22
	Forfeited	(245,835	)	$	31.29		(19,412	)	$	32.71
	Adjustment due to performance	—		$	—		37,381		$	31.24
	Non-vested balance at December 31, 2013	4,250,809		$	32.04		961,163		$	32.87
	The weighted-average grant-date fair value of the Company's restricted stock units granted during the years ended December 31, 2012 and 2011 was $31.96 and $30.46, respectively. The weighted average grant date fair value of the Company's performance stock units granted during the years ended December 31, 2012 and 2011 was $31.89 and $30.60, respectively. The total fair value of the shares distributed during the years ended December 31, 2013, 2012 and 2011 in connection with the Company's restricted stock units and performance stock units was $205.5 million, $262.6 million and $249.0 million, respectively.
	The number of vested performance stock units includes any applicable performance adjustment shares. The adjustment due to performance reflects the incremental portion of the above-target payout of performance stock units awarded in February 2011 and February 2012 (190% and 200%, respectively) that vested during 2013 either in full or on a pro-rata basis due to certain types of termination of employment. There is no adjustment due to performance for performance stock units awarded in February 2013 that vested during 2013 due to certain types of termination of employment within the calendar year of grant since the payout of such awards is at 100% of target under the award's terms and conditions.
	Restricted Stock: Restricted shares of the Company's common stock may be awarded under the 2011 Plan and are subject to restrictions on transferability and other restrictions, if any, as the Compensation Committee may impose. The Compensation Committee may also determine when and under what circumstances the restrictions may lapse and whether the participant receives the rights of a stockholder, including, without limitation, the right to vote and receive dividends. Unless the Compensation Committee determines otherwise, restricted stock that is still subject to restrictions is forfeited upon termination of employment. Shares granted, generally become unrestricted at the earlier of: (1) January 1 of the year following the vesting grant date anniversary or (2) the later of the recipient's normal or actual retirement date. For shares granted prior to 2004, the vesting grant date anniversary is ten years. For shares granted during 2004 and 2005, the vesting grant date anniversary is 7 years and 5 years, respectively. However, certain restricted shares granted in 2005 vested on the third anniversary of the grant date. There have been no restricted shares granted since 2005.
	A summary of the status of the Company's restricted stock awards as of December 31, 2013 and changes during the period then ended is presented below:
		Shares			Weighted Average
					Grant Date
					Fair Value
	Non-vested balance at January 1, 2013	31,700			$	47.31
	Granted	—			$	—
	Vested	(24,500	)		$	47.66
	Forfeited	—			$	—
	Non-vested balance at December 31, 2013	7,200			$	46.14
	The total fair value of the Company's restricted stock distributed was $1.1 million during the year ended December 31, 2013 and $0.6 million for each of the years ended December 31, 2012 and 2011.
	As of December 31, 2013, there was $73.6 million of unrecognized compensation cost related to the Company's restricted stock, restricted stock units and performance stock unit awards. The weighted-average period over which that cost is expected to be recognized is approximately one year.
	Marsh & McLennan Companies Stock Purchase Plans
	In May 1999, the Company's stockholders approved an employee stock purchase plan (the “1999 Plan”) to replace the 1994 Employee Stock Purchase Plan (the “1994 Plan”), which terminated on September 30, 1999 following its fifth annual offering. Under the current terms of the Plan, shares are purchased four times during the plan year at a price that is 95% of the average market price on each quarterly purchase date. Under the 1999 Plan, after including the available remaining unused shares in the 1994 Plan and reducing the shares available by 10,000,000 consistent with the Company's Board of Directors' action in March 2007, no more than 35,600,000 shares of the Company's common stock may be sold. Employees purchased 748,842 shares during the year ended December 31, 2013 and at December 31, 2013, 3,387,471 shares were available for issuance under the 1999 Plan. Under the 1995 Company Stock Purchase Plan for International Employees (the “International Plan”), after reflecting the additional 5,000,000 shares of common stock for issuance approved by the Company's Board of Directors in July 2002, and the addition of 4,000,000 shares due to a shareholder action in May 2007, no more than 12,000,000 shares of the Company's common stock may be sold. Employees purchased 98,863 shares during the year ended December 31, 2013 and there were 2,987,099 shares available for issuance at December 31, 2013 under the International Plan. The plans are considered non-compensatory.

Fair_Value_Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2013
Fair Value Disclosures [Abstract]	'
Fair Value Measurements	'
	Fair Value Measurements
	Fair Value Hierarchy
	The Company has categorized its assets and liabilities that are valued at fair value on a recurring basis into a three-level fair value hierarchy as defined by the FASB in 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 & 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.
	Other Sovereign Government Obligations, Municipal Bonds and Corporate Bonds - Level 2
	The investments listed in the caption above are valued on the basis of valuations furnished by an independent pricing service approved by the trustees or dealers. Such services or dealers determine valuations for normal institutional-size trading units of such securities using methods based on market transactions for comparable securities and various relationships, generally recognized by institutional traders, between securities.
	Interest Rate Swap Derivative - 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 adjusted by the fair value of the interest rate swap derivative, 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 Purchase 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 from two to four years. The fair value of contingent consideration is estimated as the present value of future cash flows that would result 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 December 31, 2013 and 2012.
	(In millions of dollars)	Identical Assets						Observable Inputs				Unobservable				Total
		(Level 1)						(Level 2)				Inputs
												(Level 3)
		12/31/13			12/31/12			12/31/13		12/31/12		12/31/13		12/31/12		12/31/13		12/31/12
	Assets:
	Financial instruments owned:
	Mutual funds(a)	$	154		$	139		$	—	$	—	$	—	$	—	$	154	$	139
	Money market funds(b)	45			483			—		—		—		—		45		483
	Interest rate swap derivatives(c)	—			—			3		6		—		—		3		6
	Total assets measured at fair value	$	199		$	622		$	3	$	6	$	—	$	—	$	202	$	628
	Fiduciary Assets:
	State and local obligations (including non-U.S. locales)	$	—		$	—		$	—	$	3	$	—	$	—	$	—	$	3
	Money market funds	—			149			—		—		—		—		—		149
	Total fiduciary assets measured at fair value	$	—		$	149		$	—	$	3	$	—	$	—	$	—	$	152
	Liabilities:
	Contingent purchase consideration liability(d)	$	—		$	—		$	—	$	—	$	104	$	63	$	104	$	63
	Senior Notes due 2014(e)	$	—		$	—		$	253	$	256	$	—	$	—	$	253	$	256
	Total liabilities measured at fair value	$	—		$	—		$	253	$	256	$	104	$	63	$	357	$	319
	(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 year ended December 31, 2013, there were no assets or liabilities that 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 for the years ended December 31, 2013 and December 31, 2012 that represent contingent purchase consideration related to acquisitions:
	(In millions of dollars)	2013			2012
	Balance at January 1,	$	63		$	110
	Additions	26			27
	Payments	(17		)	(30		)
	Revaluation Impact	32			(44		)
	Balance at December 31,	$	104		$	63
	The fair value of the contingent purchase consideration 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 $32 million for the year ended December 31, 2013. A 5% increase in the above mentioned projections would increase the liability by approximately $8 million. A 5% decrease in the above mentioned projections would decrease the liability by approximately $9 million.
	Fair Value of Long-term Investments
	The Company has certain long-term investments, primarily related to investments in non-publicly traded private equity funds of $14 million and $16 million at December 31, 2013 and December 31, 2012, respectively, carried on the cost basis for which there are no readily available market prices. The carrying values of these investments approximates 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. These investments would be classified as Level 3 in the fair value hierarchy and are included in Other assets in the consolidated balance sheets.

LongTerm_Commitments

Long-Term Commitments	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Long-Term Commitments	'
	Long-term Commitments
	The Company leases office facilities, equipment and automobiles under non-cancelable operating leases. These leases expire on varying dates; in some instances contain renewal and expansion options; do not restrict the payment of dividends or the incurrence of debt or additional lease obligations; and contain no significant purchase options. In addition to the base rental costs, occupancy lease agreements generally provide for rent escalations resulting from increased assessments for real estate taxes and other charges. Approximately 98% of the Company’s lease obligations are for the use of office space.
	The consolidated statements of income include net rental costs of $403 million, $416 million and $430 million for 2013, 2012 and 2011, respectively, after deducting rentals from subleases ($13 million in 2013, $10 million in 2012 and $9 million in 2011). These net rental costs exclude rental costs and sublease income for previously accrued restructuring charges related to vacated space.
	At December 31, 2013, the aggregate future minimum rental commitments under all non-cancelable operating lease agreements are as follows:
	For the Years Ended December 31,	Gross		Rentals		Net
		Rental		from		Rental
	(In millions of dollars)	Commitments		Subleases		Commitments
	2014	$	398	$	52	$	346
	2015	$	357	$	46	$	311
	2016	$	318	$	45	$	273
	2017	$	273	$	42	$	231
	2018	$	244	$	40	$	204
	Subsequent years	$	1,101	$	86	$	1,015
	The Company has entered into agreements, primarily with various service companies, to outsource certain information systems activities and responsibilities and processing activities. Under these agreements, the Company is required to pay minimum annual service charges. Additional fees may be payable depending upon the volume of transactions processed, with all future payments subject to increases for inflation. At December 31, 2013, the aggregate fixed future minimum commitments under these agreements are as follows:
	For the Years Ended December 31,	Future
		Minimum
	(In millions of dollars)	Commitments
	2014	$	285
	2015	119
	2016	102
	Subsequent years	170
		$	676

Debt

Debt	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Debt	'
	Debt
	The Company’s outstanding debt is as follows:
	December 31,
	(In millions of dollars)	2013			2012
	Short-term:
	Current portion of long-term debt	$	334		$	260
	Long-term:
	Senior notes – 4.850% due 2013	—			250
	Senior notes – 5.875% due 2033	297			296
	Senior notes – 5.375% due 2014	323			326
	Senior notes – 5.75% due 2015	230			479
	Senior notes – 2.30% due 2017	249			249
	Senior notes – 9.25% due 2019	399			398
	Senior notes – 4.80% due 2021	497			497
	Senior notes - 2.55% due 2018	248			—
	Senior notes - 4.05% due 2023	247			—
	Mortgage – 5.70% due 2035	413			422
	Term Loan Facility - due 2016	50			—
	Other	2			1
		2,955			2,918
	Less current portion	334			260
		$	2,621		$	2,658
	The senior notes in the table above are publically 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 that matured using cash.
	During the first quarter of 2012, the Company repaid its 6.25% fixed rate $250 million senior notes that matured. The Company used proceeds from the issuance of 2.3% five-year $250 million senior notes in the first quarter of 2012 to fund the maturing notes.
	The Company and certain of its foreign subsidiaries maintain a $1.0 billion multi-currency unsecured revolving credit facility which expires in October 2016. The interest rate on this facility is based on LIBOR plus a fixed margin which varies with the Company's credit ratings. This facility requires the Company to maintain certain coverage and leverage ratios which are tested quarterly. There were no borrowings outstanding under this facility at December 31, 2013.
	In December 2012, the Company closed on a $50 million, three-year term loan facility. The interest rate on this facility at December 31, 2013 was 1.29%, 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 December 31, 2013.
	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 periods ended December 31, 2013 and 2012 is as follows:
		2013							2012
	Income statement classification	Loss on			Gain on		Net		Loss on			Gain on		Net
	(In millions of dollars)	Swaps			Notes		Income		Swaps			Notes		Income
							Effect							Effect
	Other Operating Expenses	$	(3	)	$	3	$	—	$	(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.
	Additional credit facilities, guarantees and letters of credit are maintained with various banks, primarily related to operations located outside the United States, aggregating $282 million at December 31, 2013 and $247 million at December 31, 2012. There was $1 million outstanding borrowings under these facilities at December 31, 2013 and no outstanding borrowings under these facilities at December 31, 2012.
	Scheduled repayments of long-term debt in 2014 and in the four succeeding years are $331 million, $241 million, $61 million, $262 million and $262 million, respectively.
	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.
		December 31, 2013					December 31, 2012
	(In millions of dollars)	Carrying			Fair		Carrying		Fair
		Amount			Value		Amount		Value
	Short-term debt	$	334		$	334	$	260	$	261
	Long-term debt	$	2,621		$	2,819	$	2,658	$	2,986
	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.

Integration_and_Restructuring_

Integration and Restructuring Costs	12 Months Ended
	Dec. 31, 2013
Restructuring and Related Activities [Abstract]	'
Integration and Restructuring Costs	'
	Integration and Restructuring Costs
	In 2013, the Company implemented restructuring actions which resulted in costs totaling $22 million. Restructuring costs consist primarily of severance and benefits, costs for future rent and other real estate costs. These costs were incurred as follows: Risk and Insurance Services—$7 million; Consulting—$2 million; and Corporate—$13 million.
	Details of the restructuring liability activity from January 1, 2012 through December 31, 2013, including actions taken prior to 2013 are as follows:
	(In millions of dollars)	Balance at		Expense		Cash			Other			Balance at		Expense		Cash			Other			Balance at
		1/1/12		Incurred		Paid						12/31/12		Incurred		Paid						12/31/13
	Severance	$	27	$	46	$	(38	)	$	1		$	36	$	9	$	(33	)	$	(1	)	$	11
	Future rent under non-cancelable leases and other costs	154		32		(50		)	(2		)	134		13		(32		)	(2		)	113
	Total	$	181	$	78	$	(88	)	$	(1	)	$	170	$	22	$	(65	)	$	(3	)	$	124
	As of January 1, 2011, the liability balance related to restructuring activity was $211 million. In 2011, the Company accrued $51 million and had cash payments of $82 million related to restructuring activities that resulted in the liability balance at January 1, 2012 reported above.
	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 and employee benefits, depending on the nature of the items.

Common_Stock

Common Stock	12 Months Ended
	Dec. 31, 2013
Equity [Abstract]	'
Common Stock	'
	Common Stock
	During 2013, the Company repurchased 13.2 million shares of its common stock for total consideration of $550 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 $563 million. There is no time limit on the authorization. During 2012, the Company purchased 6.9 million shares of its common stock for total consideration of $230 million.

Claims_Lawsuits_And_Other_Cont

Claims, Lawsuits And Other Contingencies	12 Months Ended
	Dec. 31, 2013
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, 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 December 31, 2013, 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	12 Months Ended
	Dec. 31, 2013
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 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. 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 segments and geographic areas of operation are as follows:
	For the Year Ended December 31, (In millions of dollars)	Revenue				Operating				Total				Depreciation		Capital
						Income				Assets				and		Expenditures
						(Loss)								Amortization
	2013 –
	Risk and Insurance Services	$	6,596		(a)	$	1,421			$	11,365			$	192	$	158
	Consulting	5,701			(b)	845				5,178				115		155
	Total Segments	12,297				2,266				16,543				307		313
	Corporate / Eliminations	(36		)	(c)	(189		)	(c)	437			(d)	51		88
	Total Consolidated	$	12,261			$	2,077			$	16,980			$	358	$	401
	2012 –
	Risk and Insurance Services	$	6,350		(a)	$	1,334			$	9,832			$	196	$	131
	Consulting	5,613			(b)	692				5,203				113		117
	Total Segments	11,963				2,026				15,035				309		248
	Corporate / Eliminations	(39		)	(c)	(197		)	(c)	1,253			(d)	40		72
	Total Consolidated	$	11,924			$	1,829			$	16,288			$	349	$	320
	2011 –
	Risk and Insurance Services	$	6,079		(a)	$	1,200			$	9,102			$	189	$	146
	Consulting	5,487			(b)	617				4,820				112		91
	Total Segments	11,566				1,817				13,922				301		237
	Corporate / Eliminations	(40		)	(c)	(179		)	(c)	1,532			(d)	31		43
	Total Consolidated	$	11,526			$	1,638			$	15,454			$	332	$	280
	(a)	Includes inter-segment revenue of $5 million in both 2013 and 2012 and $4 million in 2011, interest income on fiduciary funds of $27 million, $39 million and $47 million in 2013, 2012 and 2011, respectively, and equity method income of $8 million, $11 million and $14 million in 2013, 2012 and 2011, respectively.
	(b)	Includes inter-segment revenue of $31 million, $34 million and $36 million in 2013, 2012 and 2011, respectively, and interest income on fiduciary funds of $5 million in 2013, and $4 million in both 2012 and 2011.
	(c)	Includes results of corporate advisory and restructuring business.
	(d)	Corporate assets primarily include insurance recoverables, pension related assets, the owned portion of the Company headquarters building and intercompany eliminations.
	Details of operating segment revenue are as follows:
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Risk and Insurance Services
	Marsh	$	5,461			$	5,265			$	5,031
	Guy Carpenter	1,135				1,085				1,048
	Total Risk and Insurance Services	6,596				6,350				6,079
	Consulting
	Mercer	4,241				4,147				4,004
	Oliver Wyman Group	1,460				1,466				1,483
	Total Consulting	5,701				5,613				5,487
	Total Segments	12,297				11,963				11,566
	Corporate/ Eliminations	(36		)		(39		)		(40		)
	Total	$	12,261			$	11,924			$	11,526
	Information by geographic area is as follows:
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Revenue
	United States	$	5,485			$	5,300			$	5,131
	United Kingdom	1,979				1,960				1,922
	Continental Europe	1,943				1,879				1,906
	Asia Pacific	1,396				1,346				1,287
	Other	1,494				1,478				1,320
		12,297				11,963				11,566
	Corporate/Eliminations	(36		)		(39		)		(40		)
		$	12,261			$	11,924			$	11,526
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Fixed Assets, Net
	United States	$	494			$	494			$	505
	United Kingdom	121				121				133
	Continental Europe	64				63				65
Asia Pacific	72				62				37
Other	77				69				64
	$	828			$	809			$	804

Summary_of_Significant_Account1

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2013
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.
Principles of Consolidation	'
	Principles of Consolidation:  The accompanying consolidated financial statements include all wholly-owned and majority-owned subsidiaries. All significant inter-company transactions and balances have been eliminated.
Fiduciary Assets And Liabilities	'
	Fiduciary Assets and Liabilities:  In its capacity as an insurance broker or agent, the Company generally 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 $27 million, $39 million and $47 million in 2013, 2012 and 2011, respectively. The Consulting segment recorded fiduciary interest income of $5 million in 2013 and $4 million in both 2012 and 2011. 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 $8.2 billion and $9.1 billion at December 31, 2013 and 2012, respectively. 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 $16 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.
Revenue	'
	Revenue:  Risk and Insurance Services revenue includes insurance commissions, fees for services rendered and interest income on certain fiduciary funds. Insurance commissions and fees for risk transfer services generally are recorded as of the effective date of the applicable policies or, in certain cases (primarily in the Company's reinsurance broking operations), as of the effective date or billing date, whichever is later. A reserve for policy cancellation is provided based on historic and current data on cancellations. Fees for non-risk transfer services provided to clients are recognized over the period in which the services are provided, using a proportional performance model. Fees resulting from achievement of certain performance thresholds are recorded when such levels are attained and such fees are not subject to forfeiture.
	Consulting revenue includes fees paid by clients for advice and services and commissions from insurance companies for the placement of individual and group contracts. Fee revenue for engagements where remuneration is based on time plus out-of-pocket expenses is recognized based on the amount of time consulting professionals expend on the engagement. For fixed fee engagements, revenue is recognized using a proportional performance model. Revenue from insurance commissions not subject to a fee arrangement is recorded over the effective period of the applicable policies. Revenue for asset based fees is recognized on an accrual basis by applying the daily/monthly rate as contractually agreed with the client to the applicable net asset value. On a limited number of engagements, performance fees may also be earned for achieving certain prescribed performance criteria. Such fees are recognized when the performance criteria have been achieved and agreed to by the client. Reimbursable expenses incurred by professional staff in the generation of revenue and sub-advisory fees related to investment management are included in revenue and the related expenses are included in other operating expenses.
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. 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.
Fixed Assets	'
	Fixed Assets:  Fixed assets are stated at cost less accumulated depreciation and amortization. Expenditures for improvements are capitalized. Upon sale or retirement, the cost and related accumulated depreciation and amortization are removed from the accounts and any gain or loss is reflected in income. Expenditures for maintenance and repairs are charged to operations as incurred.
	Depreciation of buildings, building improvements, furniture, and equipment is provided on a straight-line basis over the estimated useful lives of these assets. Furniture and equipment is depreciated over periods ranging from three to ten years. Leasehold improvements are amortized on a straight-line basis over the periods covered by the applicable leases or the estimated useful life of the improvement, whichever is less. Buildings are depreciated over periods ranging from thirty to forty years. The Company periodically reviews long-lived assets for impairment whenever events or changes indicate that the carrying value of assets may not be recoverable.
Investments	'
	Investments:  The Company holds investments primarily in private companies and certain private equity funds.
	Certain investments, primarily investments in private equity funds, are accounted for under the equity method using a consistently applied three-month lag period adjusted for any known significant changes from the lag period to the reporting date of the Company. The underlying private equity funds follow investment company accounting, where investments within the fund are carried at fair value. The Company records in earnings, investment gains/losses for its proportionate share of the change in fair value of the funds, which amounted to gains of $12 million, $33 million and $10 million in 2013, 2012 and 2011, respectively. Investments recorded using the equity method are included in other assets in the consolidated balance sheets.
	As part of the sale of MMC Capital in 2005, the Company retained the right to receive certain performance fees related to the Trident II and Trident III private equity partnerships. The Company recognizes performance fee income when such fees are no longer subject to forfeiture, which may take a number of years to resolve. The Company deferred the recognition of income related to such performance fees of $38 million and $63 million at December 31, 2013 and 2012, respectively, related to Trident III. This income is based on the investment performance over the life of each investment in the private equity fund, and future declines in fund performance from current levels may result in the forfeiture of such revenue. Trident II has now fully harvested all its portfolio investments and final distributions were made to partners during the fourth quarter of 2013. Therefore, the Company no longer holds an investment in Trident II. Approximately $40 million and $15 million of performance fees were recognized in 2013 related to Trident III and Trident II, respectively, and included as part of investment income. The Company received approximately $100 million in cash proceeds related to Trident II partnership distributions in 2013.
	Gains or losses recognized in earnings from the investments, including the performance fees discussed above, are included in investment income in the consolidated statements of income.
Goodwill and Intangible Assets	'
	Goodwill and Other Intangible Assets:  Goodwill represents acquisition costs in excess of the fair value of net assets acquired. Goodwill is reviewed at least annually for impairment. The Company performs an annual impairment test for each of its reporting units during the third quarter of each year. When a step 1 test is performed, fair values of the reporting units are estimated using either a market approach or a discounted cash flow model. 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. As discussed in Note 6, the Company may elect to assess qualitative factors to determine if a step 1 assessment is necessary. Other intangible assets, which primarily consist of customer lists, 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.
Capitalized Software Costs	'
	Capitalized Software Costs:  The Company capitalizes certain costs to develop, purchase or modify software for the internal use of the Company. These costs are amortized on a straight-line basis over periods ranging from 3 to 10 years. Costs incurred during the preliminary project stage and post implementation stage, are expensed as incurred. Costs incurred during the application development stage are capitalized. Costs related to updates and enhancements are only capitalized if they will result in additional functionality. Capitalized computer software costs of $399 million and $278 million, net of accumulated amortization of $748 million and $691 million at December 31, 2013 and 2012, respectively, are included in other assets in the consolidated balance sheets.
Legal and Other Loss Contingencies	'
	Legal and Other Loss Contingencies:  The Company and its subsidiaries are subject to a significant number of claims, lawsuits and proceedings including claims for errors and omissions ("E&O"). GAAP requires that a liability be recorded when a loss is both probable and reasonably estimable. Significant management judgment is required to apply this guidance. The Company utilizes case level reviews by inside and outside counsel, an internal actuarial analysis and other analysis to estimate potential losses. 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. Given the unpredictability of E&O claims and of litigation that could flow from them, it is possible that an adverse outcome in a particular matter could have a material adverse effect on the Company’s businesses, results of operations, financial condition or cash flow in a given quarterly or annual period.
	In addition, to the extent that insurance coverage is available, significant management judgment is required to determine the amount of recoveries that are probable of collection under the Company’s various insurance programs.
	The legal and other contingent liabilities described above are not discounted.
Income Taxes	'
	Income Taxes:  The Company's effective tax rate reflects its income, statutory tax rates and tax planning in the various jurisdictions in which it operates. Significant judgment is required in determining the annual effective tax rate and in evaluating uncertain tax positions and the ability to realize deferred tax assets.
	The Company reports a liability for unrecognized tax benefits resulting from uncertain tax positions taken or expected to be taken in a tax return. The evaluation of a tax position is a two-step process. The first step involves recognition. The Company determines whether it is more likely than not that a tax position will be sustained upon tax examination, including resolution of any related appeals or litigation, based on only the technical merits of the position. The technical merits of a tax position derive from both statutory and judicial authority (legislation and statutes, legislative intent, regulations, rulings, and case law) and their applicability to the facts and circumstances of the tax position. If a tax position does not meet the more likely than not recognition threshold, the benefit of that position is not recognized in the financial statements. The second step is measurement. A tax position that meets the more likely than not recognition threshold is measured to determine the amount of benefit to recognize in the financial statements. The tax position is measured as the largest amount of benefit that is greater than 50 percent likely of being realized upon ultimate resolution with a taxing authority.
	Uncertain tax positions are evaluated based upon the facts and circumstances that exist at each reporting period. Subsequent changes in judgment based upon new information may lead to changes in recognition, de-recognition, and measurement. Adjustments may result, for example, upon resolution of an issue with the taxing authorities, or expiration of a statute of limitations barring an assessment for an issue. The Company recognizes interest and penalties, if any, related to unrecognized tax benefits in income tax expense.
	Tax law requires items be included in the Company's tax returns at different times than the items are reflected in the financial statements. As a result, the annual tax expense reflected in the consolidated statements of income is different than that reported in the income tax returns. Some of these differences are permanent, such as expenses that are not deductible in the returns, and some differences are temporary and reverse over time, such as depreciation expense. Temporary differences create deferred tax assets and liabilities. Deferred tax assets generally represent items that can be used as a tax deduction or credit in tax returns in future years for which benefit has already been recorded in the financial statements. Valuation allowances are established for deferred tax assets when it is estimated that future taxable income will be insufficient to use a deduction or credit in that jurisdiction. Deferred tax liabilities generally represent tax expense recognized in the financial statements for which payment has been deferred, or expense for which a deduction has been taken already in the tax return but the expense has not yet been recognized in the financial statements.
Derivative Instruments	'
	Derivative Instruments:  All derivatives, whether designated in hedging relationships or not, are recorded on the balance sheet at fair value. If the derivative is designated as a fair value hedge, the changes in the fair value of the derivative and of the hedged item attributable to the hedged risk are recognized in earnings. If the derivative is designated as a cash flow hedge, the effective portions of changes in the fair value of the derivative are recorded in other comprehensive income and are recognized in the income statement when the hedged item affects earnings. Changes in the fair value attributable to the ineffective portion of cash flow hedges are recognized in earnings.
Concentrations Of Credit Risk	'
	Concentrations of Credit Risk:  Financial instruments which potentially subject the Company to concentrations of credit risk consist primarily of cash and cash equivalents, commissions and fees receivable and insurance recoverables. The Company maintains a policy providing for the diversification of cash and cash equivalent investments and places its investments in a large number of high quality financial institutions to limit the amount of credit risk exposure. Concentrations of credit risk with respect to receivables are generally limited due to the large number of clients and markets in which the Company does business, as well as the dispersion across many geographic areas.
Per Share Data	'
	Per Share Data: From 2009 through 2012, the Company used the two-class method to compute basic and diluted earnings per share ("EPS"). Under the accounting guidance which applies to the calculation of EPS for share-based payment awards with rights to dividends or dividend equivalents, unvested share-based payment awards that contain non-forfeitable rights to dividends or dividend equivalents (whether paid or unpaid) are participating securities and should be included in the computation of basic and dilutive EPS using the two-class method.
	In the first quarter of 2013, the share-based payment awards with non-forfeitable rights to dividends became fully vested. As a result, the Company is no longer required to use the two-class method and in the first quarter of 2013 used the treasury stock method to calculate EPS. There was no difference in the earnings per share calculations when comparing the two-class method to the treasury stock method for the years ended 2012 and 2011. Therefore, the prior period information in the chart below shows the earnings per share calculation using the treasury stock method, consistent with current year presentation.
	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 attributable to common shares 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 attributable to common shares 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.
Estimates	'
	Estimates:  The preparation of financial statements in conformity with accounting principles generally accepted in the United States requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of assets and liabilities at the date of the financial statements, and the reported amounts of revenues and expenses during the reporting period. Actual results may vary from those estimates.
New Accounting Pronouncements	'
	New Accounting Pronouncements:  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 to settle taxes that would result from the disallowance of the tax position or the entity does not intend to use the deferred tax asset for this purpose (provided that the tax law permits a choice), 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 will affect balance sheet classification and footnote disclosure only and is not expected to have a material impact on the Company's financial statements.
	In June 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 15, 2013. Earlier application is prohibited. Adoption of the guidance is not expected to materially affect the Company's financial position, results of operations or cash flows.
	In February 2013, the FASB issued new accounting guidance that adds new disclosure requirements for items reclassified out of accumulated other comprehensive income. The Company implemented this new guidance for the reporting period ended March 31, 2013. Other than enhanced disclosure, the adoption of this new guidance did not have a material effect on the Company's financial statements.
	In the first quarter of 2012, the Company adopted new accounting guidance related to the presentation of Comprehensive Income. The new guidance gives an entity the option to present the total of comprehensive income, the components of net income, and the components of other comprehensive income either in a single continuous statement of comprehensive income or in two separate but consecutive statements. In both choices, an entity is required to present each component of net income along with total net income, each component of other comprehensive income along with a total for other comprehensive income, and a total amount for comprehensive income. The guidance eliminates the option to present the components of other comprehensive income as part of the statement of changes in stockholders’ equity. The guidance did not change the items that must be reported in other comprehensive income or when an item of other comprehensive income must be reclassified to net income. Other than enhanced disclosure, adoption of this new guidance did not have a material effect on the Company's financial statements.
	In January 2012, the Company adopted guidance issued by the FASB on accounting and disclosure requirements related to fair value measurements. The guidance expands the disclosures on Level 3 inputs by requiring quantitative disclosure of the unobservable inputs and assumptions, as well as description of the valuation processes, the sensitivity of the fair value to changes in unobservable inputs and the hierarchy classification, valuation techniques, and inputs for assets and liabilities whose fair value is only disclosed in the footnotes.
	Reclassifications: Certain reclassifications have been made to prior period amounts to conform with current year presentation, in particular with regard to the Per Share Data disclosure in Footnote 1, which is presented using the treasury stock method, since there is no difference in the earnings per share calculation between the treasury stock method and the two-class method for the three years presented.

Summary_of_Significant_Account2

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2013
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'
Components of Fixed Assets	'
	The components of fixed assets are as follows:
	December 31,
	(In millions of dollars)		2013				2012
	Furniture and equipment		$	1,201			$	1,168
	Land and buildings		408				412
	Leasehold and building improvements		816				811
			2,425				2,391
	Less-accumulated depreciation and amortization		(1,597		)		(1,582		)
			$	828			$	809
Diluted Earnings per Share for Continuing Operations	'
	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
	(In millions, except per share figures)	2013				2012				2011
	Net income from continuing operations	$	1,379			$	1,204			$	982
	Less: Net income attributable to non-controlling interests	28				25				22
		$	1,351			$	1,179			$	960
	Basic weighted average common shares outstanding	549				544				542
	Dilutive effect of potentially issuable common shares	9				8				9
	Diluted weighted average common shares outstanding	558				552				551
	Average stock price used to calculate common stock equivalents	$	40.97			$	33.1			$	29.4

Supplemental_Disclosures_Table

Supplemental Disclosures (Tables)	12 Months Ended
	Dec. 31, 2013
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:
	(In millions of dollars)	2013			2012			2011
	Assets acquired, excluding cash	$	217		$	380		$	214
	Released from escrow in 2012	—			(62		)	—
	Liabilities assumed	(53		)	(42		)	(21		)
	Contingent/deferred purchase consideration	(39		)	(46		)	(33		)
	Net cash outflow for current year acquisitions	125			230			160
	Purchase of other intangibles	2			3			4
	Deferred purchase consideration from prior years' acquisitions	15			59			11
	Subtotal	$	142		$	292		$	175
	Cash paid into escrow for future acquisition	—			—			62
	Net cash outflow for acquisitions	$	142		$	292		$	237
	(In millions of dollars)	2013			2012			2011
	Interest paid	$	170		$	183		$	188
	Income taxes paid, net of refunds	$	360		$	350		$	37
Analysis of Allowance For Doubtful Accounts	'
	An analysis of the allowance for doubtful accounts is as follows:
	For the Year Ended December 31,
	(In millions of dollars)	2013			2012			2011
	Balance at beginning of year	$	106		$	105		$	114
	Provision charged to operations	16			11			11
	Accounts written-off, net of recoveries	(19		)	(12		)	(21		)
	Effect of exchange rate changes and other	(5		)	2			1
	Balance at end of year	$	98		$	106		$	105

Other_Comprehensive_Income_Los1

Other Comprehensive Income (Loss) (Tables)	12 Months Ended
	Dec. 31, 2013
Equity [Abstract]	'
Schedule of Other Comprehensive Income (Loss)	'
	The components of other comprehensive income (loss) are as follows:
	For the year ended December 31,	2013
	(In millions of dollars)	Pre-Tax			Tax (Credit)			Net of Tax
	Foreign currency translation adjustments	$	(86	)	$	(2	)	$	(84	)
	Unrealized investment gains (losses)	1			—			1
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains	(22		)	(8		)	(14		)
	Net actuarial losses	317			108			209
	Subtotal	295			100			195
	Net gains arising during period	898			339			559
	Foreign currency translation adjustments	27			8			19
	Other adjustments	(7		)	(3		)	(4		)
	Pension/post-retirement plans gains	1,213			444			769
	Other comprehensive income	$	1,128		$	442		$	686
	For the year ended December 31,	2012
	(In millions of dollars)	Pre-Tax			Tax (Credit)			Net of Tax
	Foreign currency translation adjustments	$	177		$	(5	)	$	182
	Unrealized investment losses	(1		)	1			(2		)
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains	(31		)	(12		)	(19		)
	Net actuarial losses	270			90			180
	Subtotal	239			78			161
	Net loss arising during period	(648		)	(217		)	(431		)
	Foreign currency translation adjustments	(113		)	(26		)	(87		)
	Other adjustments	75			17			58
	Pension/post-retirement plans losses	(447		)	(148		)	(299		)
	Other comprehensive loss	$	(271	)	$	(152	)	$	(119	)
	For the year ended December 31,	2011
	(In millions of dollars)	Pre-Tax			Tax (Credit)			Net of Tax
	Foreign currency translation adjustments	$	(100	)	$	4		$	(104	)
	Unrealized investment losses	(9		)	(4		)	(5		)
	Pension/post-retirement plans:
	Amortization of losses (gains) included in net periodic pension cost:
	Prior service gains	(32		)	(13		)	(19		)
	Net actuarial losses	213			68			145
	Subtotal	181			55			126
	Net loss arising during period	(1,289		)	(388		)	(901		)
	Foreign currency translation adjustments	(14		)	(3		)	(11		)
	Other adjustments	8			1			7
	Pension/post-retirement plans losses	(1,114		)	(335		)	(779		)
	Other comprehensive loss	$	(1,223	)	$	(335	)	$	(888	)
Schedule of Accumulated Other Comprehensive Income (Loss)	'
	The components of accumulated other comprehensive income (loss) are as follows:
	(In millions of dollars)	December 31, 2013				December 31, 2012
	Foreign currency translation adjustments (net of deferred tax liability of $7 and $9 in 2013 and 2012, respectively)	$	56			$	140
	Net unrealized investment gains (net of deferred tax liability of $2 in 2013 and 2012, respectively)	5				4
	Net charges related to pension / post-retirement plans (net of deferred tax asset of $1,213 and $1,657 in 2013 and 2012, respectively)	(2,682		)		(3,451		)
		$	(2,621	)		$	(3,307	)
	The changes in the balances of each component of Accumulated Other Comprehensive Income ("AOCI") for the year ended December 31, 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, 2013	$	4			$	(3,451	)		$	140		$	(3,307	)
	Other comprehensive income (loss) before reclassifications	1				574				(84		)	491
	Amounts reclassified from accumulated other comprehensive income	—				195				—			195
	Net current period other comprehensive income (loss)	1				769				(84		)	686
	Balance as of December 31, 2013	$	5			$	(2,682	)		$	56		$	(2,621	)

Acquisitions_Tables

Acquisitions (Tables)	12 Months Ended
	Dec. 31, 2013
Business Combinations [Abstract]	'
Allocation Of Acquisition Costs	'
	The following table presents the preliminary allocation of the acquisition cost to the assets acquired and liabilities assumed, based on their fair values:
	(In millions)	2013
	Cash	$	139
	Estimated fair value of deferred/contingent consideration	39
	Total Consideration	$	178
	Allocation of purchase price:
	Cash and cash equivalents	$	14
	Accounts receivable, net	10
	Other current assets	12
	Property, plant, and equipment	3
	Intangible assets (primarily customer lists amortized over 10 years)	77
	Goodwill	113
	Other assets	2
	Total assets acquired	231
	Current liabilities	21
	Other liabilities	32
	Total liabilities assumed	53
	Net assets acquired	$	178
Pro-Forma Information	'
		Years Ended December 31,
	(In millions, except per share data)	2013		2012		2011
	Revenue	$	12,424	$	12,202	$	11,778
	Income from continuing operations	$	1,387	$	1,222	$	990
	Net income attributable to the Company	$	1,365	$	1,195	$	1,001
	Basic net income per share:
	– Continuing operations	$	2.48	$	2.2	$	1.78
	– Net income attributable to the Company	$	2.49	$	2.2	$	1.84
	Diluted net income per share:
	– Continuing operations	$	2.44	$	2.16	$	1.75
	– Net income attributable to the Company	$	2.45	$	2.16	$	1.81

Discontinued_Operations_Tables

Discontinued Operations (Tables)	12 Months Ended
	Dec. 31, 2013
Discontinued Operations and Disposal Groups [Abstract]	'
Income Statement Data	'
	Summarized Statements of Income data for discontinued operations is as follows:
	For the Year Ended December 31,
	(In millions of dollars)	2013			2012			2011
	Income (loss) from discontinued operations, net of tax	$	—		$	—		$	(17	)
	Disposals of discontinued operations	(4		)	(2		)	25
	Income tax (credit) expense	(10		)	1			(25		)
	Disposals of discontinued operations, net of tax	6			(3		)	50
	Discontinued operations, net of tax	$	6		$	(3	)	$	33
	Discontinued operations, net of tax per share
	– Basic	$	0.01		$	—		$	0.06
	– Diluted	$	0.01		$	—		$	0.06

Goodwill_And_Other_Intangibles1

Goodwill And Other Intangibles (Tables)	12 Months Ended
	Dec. 31, 2013
Goodwill and Intangible Assets Disclosure [Abstract]	'
Changes in the Carrying Amount of Goodwill	'
	Changes in the carrying amount of goodwill are as follows:
	(In millions of dollars)	2013			2012
	Balance as of January 1, as reported	$	6,792		$	6,562
	Goodwill acquired	113			226
	Other adjustments(a)	(12		)	4
	Balance at December 31,	$	6,893		$	6,792
	(a)	Reflects increases due to the impact of foreign exchange in both years. 2013 also reflects a reduction due to purchase accounting adjustments.
Amortized Intangible Assets	'
	The gross cost and accumulated amortization at December 31, 2013 and 2012 is as follows:
	(In millions of dollars)	2013							2012
		Gross			Accumulated		Net		Gross		Accumulated		Net
		Cost			Amortization		Carrying		Cost		Amortization		Carrying
							Amount						Amount
	Amortized intangibles	$	888		$	416	$	472	$	814	$	345	$	469
Estimated Future Aggregate Amortization Expense	'
	The estimated future aggregate amortization expense is as follows:
	For the Years Ending December 31,
	(In millions of dollars)
	2014	$	77
	2015	75
	2016	68
	2017	61
	2018	58
	Subsequent years	133
		$	472

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2013
Income Tax Disclosure [Abstract]	'
Taxes on income	'
	For financial reporting purposes, income before income taxes includes the following components:
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Income before income taxes:
	U.S.	$	407			$	398			$	121
	Other	1,566				1,298				1,283
		$	1,973			$	1,696			$	1,404
	The expense (benefit) for income taxes is comprised of:
	Income taxes:
	Current–
	U.S. Federal	$	102			$	42			$	7
	Other national governments	264				336				289
	U.S. state and local	45				24				24
		411				402				320
	Deferred–
	U.S. Federal	12				(18		)		5
	Other national governments	149				89				90
	U.S. state and local	22				19				7
		183				90				102
	Total income taxes	$	594			$	492			$	422
Deferred income tax assets and liabilities	'
	The significant components of deferred income tax assets and liabilities and their balance sheet classifications are as follows:
	December 31,
	(In millions of dollars)	2013				2012
	Deferred tax assets:
	Accrued expenses not currently deductible	$	570			$	589
	Differences related to non-U.S. operations (a)	140				159
	Accrued retirement & postretirement benefits—non-U.S. operations	—				107
	Accrued retirement benefits U.S.	297				604
	Net operating losses (b)	79				104
	Income currently recognized for tax	74				75
	Foreign tax credit carryforwards	157				224
	Other	90				77
		$	1,407			$	1,939
	Deferred tax liabilities:
	Unrealized investment holding gains	$	2			$	2
	Differences related to non-U.S. operations	112				107
	Depreciation and amortization	273				245
	Accrued retirement & postretirement benefits - non-U.S. operations	89				—
	Other	3				4
		$	479			$	358
	(a)	Net of valuation allowances of $12 million in 2013 and $7 million in 2012.
	(b)	Net of valuation allowances of $70 million in 2013 and $65 million in 2012.
	December 31,
	(In millions of dollars)	2013				2012
	Balance sheet classifications:
	Current assets	$	482			$	410
	Other assets	$	626			$	1,223
	Current liabilities	$	(18	)		$	(18	)
	Other liabilities	$	(162	)		$	(34	)
U.S. Federal statutory income tax rate	'
	A reconciliation from the U.S. Federal statutory income tax rate to the Company’s effective income tax rate is shown below.
	For the Years Ended December 31,	2013			2012			2011
	U.S. Federal statutory rate	35	%		35	%		35	%
	U.S. state and local income taxes—net of U.S. Federal income tax benefit	2.1			1.9			1.6
	Differences related to non-U.S. operations	(6.0	)		(6.1	)		(6.5	)
	Other	(1.0	)		(1.8	)		—
	Effective tax rate	30.1	%		29	%		30.1	%
Unrecognized tax benefits	'
	Following is a reconciliation of the Company’s total gross unrecognized tax benefits for the years ended December 31, 2013, 2012 and 2011:
	(In millions of dollars)	2013				2012				2011
	Balance at January 1,	$	117			$	143			$	199
	Additions, based on tax positions related to current year	16				26				7
	Additions for tax positions of prior years	35				35				39
	Reductions for tax positions of prior years	(7		)		(41		)		(91		)
	Settlements	(3		)		(6		)		(6		)
	Lapses in statutes of limitation	(30		)		(40		)		(5		)
	Balance at December 31,	$	128			$	117			$	143

Retirement_Benefits_Tables

Retirement Benefits (Tables)	12 Months Ended
	Dec. 31, 2013
Defined Benefit Pension Plans and Defined Benefit Postretirement Plans Disclosure [Abstract]	'
Schedule of weighted average actuarial assumptions utilized defined benefit plans	'
	The weighted average actuarial assumptions utilized in determining the above amounts for the U.S. defined benefit and other U.S. postretirement plans as of the end of the year are as follows:
		U.S. Pension						U.S. Postretirement Benefits
		Benefits
		2013			2012			2013			2012
	Weighted average assumptions:
	Discount rate (for expense)	4.45	%		5.15	%		4.25	%		5.1	%
	Expected return on plan assets	8.75	%		8.75	%		—			—
	Rate of compensation increase (for expense)	2	%		2	%		—			—
	Discount rate (for benefit obligation)	5.3	%		4.45	%		5.17	%		4.25	%
	Rate of compensation increase (for benefit obligation)	2	%		2	%		—			—
	The weighted average actuarial assumptions utilized for the U.S. and significant non-U.S. defined benefit plans and postretirement benefit plans are as follows:
		Pension						Postretirement
		Benefits						Benefits
		2013			2012			2013			2012
	Weighted average assumptions:
	Discount rate (for expense)	4.38	%		4.91	%		4.32	%		5.05	%
	Expected return on plan assets	7.68	%		8.03	%		—			—
	Rate of compensation increase (for expense)	2.43	%		3.09	%		—			—
	Discount rate (for benefit obligation)	4.82	%		4.38	%		5.03	%		4.32	%
	Rate of compensation increase (for benefit obligation)	2.64	%		2.43	%		—			—
	The weighted average actuarial assumptions utilized for the non-U.S. defined and postretirement benefit plans as of the end of the year are as follows:
		Non-U.S. Pension						Non-U.S.
		Benefits						Postretirement Benefits
		2013			2012			2013			2012
	Weighted average assumptions:
	Discount rate (for expense)	4.33	%		4.77	%		4.45	%		4.95	%
	Expected return on plan assets	7.17	%		7.68	%		—			—
	Rate of compensation increase (for expense)	2.69	%		3.73	%		—			—
	Discount rate (for benefit obligation)	4.55	%		4.33	%		4.8	%		4.45	%
	Rate of compensation increase (for benefit obligation)	2.99	%		2.69	%		—			—
Schedule of components of net periodic benefit cost for U.S. defined benefit and other postretirement benefit plans	'
	The components of the net periodic benefit cost for the non-U.S. defined benefit and other postretirement benefit plans and the curtailment, settlement and termination expenses are as follows:
	For the Years Ended December 31,	Non-U.S. Pension											Non-U.S. Postretirement
		Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Service cost	$	148			$	147			$	143		$	2		$	2		$	2
	Interest cost	352				366				378			4			5			5
	Expected return on plan assets	(587		)		(583		)		(572		)	—			—			—
	Amortization of prior service cost	(6		)		(3		)		(3		)	—			(1		)	—
	Recognized actuarial loss	108				118				115			2			1			—
	Net periodic benefit cost	15				45				61			8			7			7
	Settlement loss	—				1				—			—			—			—
	Curtailment credit	—				(1		)		—			—			—			—
	Special termination benefits	—				—				—			—			—			—
	Total cost	$	15			$	45			$	61		$	8		$	7		$	7
	The components of the net periodic benefit cost for defined benefit and other postretirement plans are as follows:
	Combined U.S. and significant non-U.S. Plans	Pension											Postretirement
	For the Years Ended December 31,	Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Service cost	$	252			$	240			$	226		$	5		$	5		$	5
	Interest cost	581				596				609			11			13			13
	Expected return on plan assets	(911		)		(905		)		(887		)	—			—			—
	Amortization of prior service credit	(22		)		(19		)		(19		)	—			(14		)	(13		)
	Recognized actuarial loss (credit)	315				270				215			2			—			(4		)
	Net periodic benefit cost	$	215			$	182			$	144		$	18		$	4		$	1
	The components of the net periodic benefit cost for the U.S. defined benefit and other postretirement benefit plans are as follows:
	U.S. Plans only	Pension											Postretirement
	For the Years Ended December 31,	Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Service cost	$	104			$	93			$	83		$	3		$	3		$	3
	Interest cost	229				230				231			7			8			8
	Expected return on plan assets	(324		)		(322		)		(315		)	—			—			—
	Amortization of prior service credit	(16		)		(16		)		(16		)	—			(13		)	(13		)
	Recognized actuarial loss (credit)	207				152				100			—			(1		)	(4		)
	Net periodic benefit cost (credit)	$	200			$	137			$	83		$	10		$	(3	)	$	(6	)
Schedule of MMC's defined benefit plans and postretirement plans	'
	The following schedules provide information concerning the Company’s non-U.S. defined benefit pension plans and non-U.S. postretirement benefit plans:
		Non-U.S. Pension								Non-U.S.
		Benefits								Postretirement Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Change in benefit obligation:
	Benefit obligation at beginning of year	$	8,579			$	7,717			$	107		$	91
	Service cost	148				147				2			2
	Interest cost	352				366				4			5
	Employee contributions	11				11				—			—
	Actuarial (gain) loss	(53		)		419				(8		)	10
	Plan amendments	—				(71		)		—			—
	Effect of settlement	(2		)		(11		)		—			—
	Effect of curtailment	—				(3		)		—			(1		)
	Benefits paid	(293		)		(278		)		(4		)	(4		)
	Foreign currency changes	(31		)		280				(4		)	4
	Other	—				2				—			—
	Benefit obligation December 31	$	8,711			$	8,579			$	97		$	107
	Change in plan assets:
	Fair value of plan assets at beginning of year	$	8,312			$	7,206			$	—		$	—
	Actual return on plan assets	698				721				—			—
	Effect of settlement	(2		)		(11		)		—			—
	Company contributions	620				389				4			4
	Employee contributions	11				11				—			—
	Benefits paid	(293		)		(278		)		(4		)	(4		)
	Foreign currency changes	5				273				—			—
	Other	—				1				—			—
	Fair value of plan assets, December 31	$	9,351			$	8,312			$	—		$	—
	Net funded status, December 31	$	640			$	(267	)		$	(97	)	$	(107	)
	Amounts recognized in the consolidated balance sheets:
	Non-current assets	$	977			$	258			$	—		$	—
	Current liabilities	(5		)		(6		)		(4		)	(4		)
	Non-current liabilities	(332		)		(519		)		(93		)	(103		)
	Net asset (liability) recognized, December 31	$	640			$	(267	)		$	(97	)	$	(107	)
	Amounts recognized in other comprehensive income (loss):
	Prior service credit	$	85			$	93			$	—		$	—
	Net actuarial (loss) gain	(3,010		)		(3,309		)		(16		)	(27		)
	Total recognized accumulated other comprehensive (loss) income, December 31	$	(2,925	)		$	(3,216	)		$	(16	)	$	(27	)
	Cumulative employer contributions in excess (deficient) of net periodic cost	3,565				2,949				(81		)	(80		)
	Net asset (liability) recognized in consolidated balance sheet, December 31	$	640			$	(267	)		$	(97	)	$	(107	)
	Accumulated benefit obligation, December 31	$	8,413			$	8,229			$	—		$	—
		Non-U.S. Pension								Non-U.S.
		Benefits								Postretirement Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of prior service credit (cost):
	Beginning balance	$	93			$	23			$	—		$	1
	Recognized as component of net periodic benefit credit	(6		)		(3		)		—			(1		)
	Effect of curtailment	—				(1		)		—			—
	Changes in plan assets and benefit obligations recognized in other comprehensive income:
	Plan amendments	—				71				—			—
	Exchange rate adjustments	(2		)		3				—			—
	Prior service credit, December 31	$	85			$	93			$	—		$	—
		Non-U.S. Pension								Non-U.S.
		Benefits								Postretirement Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of net actuarial gain (loss):
	Beginning balance	$	(3,309	)		$	(3,038	)		$	(27	)	$	(19	)
	Recognized as component of net periodic benefit cost	108				118				2			1
	Effect of settlement	—				1				—			—
	Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
	Liability experience	53				(419		)		8			(10		)
	Asset experience	111				138				—			—
	Effect of curtailment	—				3				—			1
	Total amount recognized as change in plan assets and benefit obligations	164				(278		)		8			(9		)
Exchange rate adjustments	27				(112		)		1			—
Net actuarial gain (loss), December 31	$	(3,010	)		$	(3,309	)		$	(16	)	$	(27	)
For the Years Ended December 31,	Non-U.S. Pension											Non-U.S. Postretirement
	Benefits											Benefits
(In millions of dollars)	2013				2012				2011			2013			2012			2011
Total recognized in net periodic benefit cost and other comprehensive (income) loss	$	(276	)		$	246			$	792		$	(2	)	$	16		$	12
The following schedules provide information concerning the Company’s U.S. defined benefit pension plans and postretirement benefit plans:
	U.S. Pension								U.S.  Postretirement
	Benefits								Benefits
(In millions of dollars)	2013				2012				2013			2012
Change in benefit obligation:
Benefit obligation at beginning of year	$	5,197			$	4,533			$	176		$	162
Service cost	104				93				3			3
Interest cost	229				230				7			8
Plan combination	36				—				—			—
Actuarial (gain) loss	(547		)		522				(15		)	13
Medicare Part D subsidy	—				—				1			3
Benefits paid	(192		)		(181		)		(14		)	(13		)
Benefit obligation, December 31	$	4,827			$	5,197			$	158		$	176
Change in plan assets:
Fair value of plan assets at beginning of year	$	3,936			$	3,493			$	—		$	—
Plan combination	21				—				—			—
Actual return on plan assets	488				500				—			—
Employer contributions	26				124				13			10
Medicare Part D subsidy	—				—				1			3
Benefits paid	(192		)		(181		)		(14		)	(13		)
Fair value of plan assets, December 31	$	4,279			$	3,936			$	—		$	—
Net funded status, December 31	$	(548	)		$	(1,261	)		$	(158	)	$	(176	)
Amounts recognized in the consolidated balance sheets:
Current liabilities	$	(24	)		$	(25	)		$	(8	)	$	(9	)
Noncurrent liabilities	(524		)		(1,236		)		(150		)	(167		)
Net liability recognized, December 31	$	(548	)		$	(1,261	)		$	(158	)	$	(176	)
Amounts recognized in other comprehensive income (loss):
Prior service credit	$	7			$	23			$	—		$	—
Net actuarial (loss) gain	(974		)		(1,887		)		13			(2		)
Total recognized accumulated other comprehensive (loss) income, December 31	$	(967	)		$	(1,864	)		$	13		$	(2	)
Cumulative employer contributions in excess (deficient) of net periodic cost	419				603				(171		)	(174		)
Net amount recognized in consolidated balance sheet	$	(548	)		$	(1,261	)		$	(158	)	$	(176	)
Accumulated benefit obligation at December 31	$	4,753			$	5,114			$	—		$	—
	U.S. Pension								U.S.  Postretirement
	Benefits								Benefits
(In millions of dollars)	2013				2012				2013			2012
Reconciliation of prior service credit (charge) recognized in accumulated other comprehensive income (loss):
Beginning balance	$	23			$	39			$	—		$	13
Recognized as component of net periodic benefit credit	(16		)		(16		)		—			(13		)
Prior service credit, December 31	$	7			$	23			$	—		$	—
Schedule of total recognized in net periodic benefit cost and other comprehensive income (loss)	'
		Non-U.S. Pension								Non-U.S.
		Benefits								Postretirement Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of prior service credit (cost):
	Beginning balance	$	93			$	23			$	—		$	1
	Recognized as component of net periodic benefit credit	(6		)		(3		)		—			(1		)
	Effect of curtailment	—				(1		)		—			—
	Changes in plan assets and benefit obligations recognized in other comprehensive income:
	Plan amendments	—				71				—			—
	Exchange rate adjustments	(2		)		3				—			—
	Prior service credit, December 31	$	85			$	93			$	—		$	—
		U.S. Pension								U.S.  Postretirement
		Benefits								Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of net actuarial gain (loss) recognized in accumulated other comprehensive income (loss):
	Beginning balance	$	(1,887	)		$	(1,695	)		$	(2	)	$	12
	Recognized as component of net periodic benefit cost	208				152				—			(1		)
	Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
	Liability experience	541				(522		)		15			(13		)
	Asset experience	164				178				—			—
	Total gain (loss) recognized as change in plan assets and benefit obligations	705				(344		)		15			(13		)
	Net actuarial gain (loss), December 31	$	(974	)		$	(1,887	)		$	13		$	(2	)
		Non-U.S. Pension								Non-U.S.
		Benefits								Postretirement Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of net actuarial gain (loss):
	Beginning balance	$	(3,309	)		$	(3,038	)		$	(27	)	$	(19	)
	Recognized as component of net periodic benefit cost	108				118				2			1
	Effect of settlement	—				1				—			—
	Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
	Liability experience	53				(419		)		8			(10		)
	Asset experience	111				138				—			—
	Effect of curtailment	—				3				—			1
	Total amount recognized as change in plan assets and benefit obligations	164				(278		)		8			(9		)
	Exchange rate adjustments	27				(112		)		1			—
	Net actuarial gain (loss), December 31	$	(3,010	)		$	(3,309	)		$	(16	)	$	(27	)
		U.S. Pension								U.S.  Postretirement
		Benefits								Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of prior service credit (charge) recognized in accumulated other comprehensive income (loss):
	Beginning balance	$	23			$	39			$	—		$	13
	Recognized as component of net periodic benefit credit	(16		)		(16		)		—			(13		)
	Prior service credit, December 31	$	7			$	23			$	—		$	—
		U.S. Pension								U.S.  Postretirement
		Benefits								Benefits
	(In millions of dollars)	2013				2012				2013			2012
	Reconciliation of net actuarial gain (loss) recognized in accumulated other comprehensive income (loss):
	Beginning balance	$	(1,887	)		$	(1,695	)		$	(2	)	$	12
	Recognized as component of net periodic benefit cost	208				152				—			(1		)
	Changes in plan assets and benefit obligations recognized in other comprehensive income (loss):
	Liability experience	541				(522		)		15			(13		)
	Asset experience	164				178				—			—
	Total gain (loss) recognized as change in plan assets and benefit obligations	705				(344		)		15			(13		)
	Net actuarial gain (loss), December 31	$	(974	)		$	(1,887	)		$	13		$	(2	)
	For the Years Ended December 31,	U.S. Pension											U.S. Postretirement
		Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Total recognized in net periodic benefit cost and other comprehensive loss (income)	$	(696	)		$	346			$	467		$	(5	)	$	24		$	(9	)
Schedule of amounts recognized in other comprehensive income (loss)	'
	For the Years Ended December 31,	Non-U.S. Pension											Non-U.S. Postretirement
		Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Total recognized in net periodic benefit cost and other comprehensive (income) loss	$	(276	)		$	246			$	792		$	(2	)	$	16		$	12
	For the Years Ended December 31,	U.S. Pension											U.S. Postretirement
		Benefits											Benefits
	(In millions of dollars)	2013				2012				2011			2013			2012			2011
	Total recognized in net periodic benefit cost and other comprehensive loss (income)	$	(696	)		$	346			$	467		$	(5	)	$	24		$	(9	)
Schedule of change in assumed health care cost trend rates	'
	A one percentage point change in assumed health care cost trend rates would have the following effects:
	(In millions of dollars)	1 Percentage				1 Percentage
		Point Increase				Point Decrease
	Effect on total of service and interest cost components	$	—			$	—
	Effect on postretirement benefit obligation	$	2			$	(7	)
	A one percentage point change in assumed health care cost trend rates would have the following effects:
	(In millions of dollars)	1 Percentage				1 Percentage
		Point Increase				Point Decrease
	Effect on total of service and interest cost components	$	1			$	(1	)
	Effect on postretirement benefit obligation	$	10			$	(8	)
Schedule of estimated amounts that will be amortized from accumulated other comprehensive in the next fiscal year	'
	Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:
		Non-U.S. Pension				Non-U.S.
		Benefits				Postretirement Benefits
	(In millions of dollars)	2014				2014
	Prior service credit	$	(6	)		$	—
	Net actuarial loss	95				1
	Projected cost	$	89			$	1
	Estimated amounts that will be amortized from accumulated other comprehensive income in the next fiscal year:
		U.S. Pension				U.S. Postretirement
		Benefits				Benefits
	(In millions of dollars)	2014				2014
	Prior service credit	$	(7	)		$	—
	Net actuarial loss	105				1
	Projected cost	$	98			$	1
Schedule of estimated future benefit payments for its pension and postretirement benefits	'
	The Plans' estimated future benefit payments for its pension and postretirement benefits (without reduction for Medicare subsidy receipts) are as follows:
	For the Years Ended December 31,	Pension								Postretirement
		Benefits								Benefits
	(In millions of dollars)	U.S.				Non-U.S.				U.S.			Non-U.S.
	2014	$	207			$	287			$	11		$	4
	2015	$	219			$	299			$	11		$	4
	2016	$	233			$	318			$	11		$	5
	2017	$	244			$	342			$	11		$	5
	2018	$	255			$	350			$	11		$	5
	2019-2023	$	1,424			$	2,046			$	57		$	27
Summary of the U.S. and non-U.S. plans investments measured at fair value on a recurring basis	'
	The following table sets forth, by level within the fair value hierarchy, a summary of the U.S. and non-U.S. plans investments measured at fair value on a recurring basis at December 31, 2013 and 2012.
		Fair Value Measurements at December 31, 2013
	Assets (In millions of dollars)	Quoted Prices in				Significant				Significant			Total
		Active Markets				Other				Unobservable
		for Identical				Observable				Inputs
		Assets				Inputs				(Level 3)
		(Level 1)				(Level 2)
	Common/Collective trusts	$	138			$	5,649			$	151		$	5,938
	Corporate obligations	—				2,330				4			2,334
	Corporate stocks	2,434				5				1			2,440
	Private equity/partnerships	—				2				799			801
	Government securities	10				340				2			352
	Real estate	—				7				312			319
	Short-term investment funds	824				15				—			839
	Company common stock	261				—				—			261
	Other investments	35				3				238			276
	Insurance group annuity contracts	—				—				—			—
	Swaps	—				2				—			2
	Total investments	$	3,702			$	8,353			$	1,507		$	13,562
		Fair Value Measurements at December 31, 2012
	Assets (In millions of dollars)	Quoted Prices in				Significant				Significant			Total
		Active Markets				Other				Unobservable
		for Identical				Observable				Inputs
		Assets				Inputs				(Level 3)
		(Level 1)				(Level 2)
	Common/Collective trusts	$	16			$	5,376			$	—		$	5,392
	Corporate obligations	—				2,236				1			2,237
	Corporate stocks	2,005				4				9			2,018
	Private equity/partnerships	2				2				824			828
	Government securities	9				309				—			318
	Real estate	11				8				357			376
	Short-term investment funds	410				4				—			414
	Company common stock	276				—				—			276
	Other investments	11				112				216			339
	Insurance group annuity contracts	—				—				23			23
	Swaps	—				4				—			4
	Total investments	$	2,740			$	8,055			$	1,430		$	12,225
Summary of changes in the fair value of the plans' Level 3 assets	'
	The tables below set forth a summary of changes in the fair value of the plans’ Level 3 assets for the years ended December 31, 2013 and December 31, 2012:
	Assets (In millions)	Fair Value,				Purchases				Sales			Unrealized			Realized			Exchange			Transfers			Fair
		1-Jan-13											Gain/			Gain/			Rate			in/(out)			Value, December 31, 2013
													(Loss)			(Loss)			Impact			and
																						Other
	Private equity/Partnerships	$	824			$	146			$	(174	)	$	(155	)	$	150		$	(1	)	$	9		$	799
	Real estate	357				21				(95		)	6			26			(3		)	—			312
	Other investments	216				18				(13		)	11			—			6			—			238
	Common/Collective Trusts	—				61				—			(4		)	—			(5		)	99			151
	Insurance group annuity contracts	23				—				—			(1		)	—			—			(22		)	—
	Corporate stocks	9				—				—			—			—			—			(8		)	1
	Corporate obligations	1				1				—			—			—			—			2			4
	Government Securities	—				—				—			(1		)	—			—			3			2
	Total assets	$	1,430			$	247			$	(282	)	$	(144	)	$	176		$	(3	)	$	83		$	1,507
	Assets (In millions)	Fair Value,				Purchases				Sales			Unrealized			Realized			Exchange			Transfers			Fair
		1-Jan-12											Gain/			Gain/			Rate			in/(out)			Value,
													(Loss)			(Loss)			Impact			and			31-Dec-12
																						Other
	Private equity/Partnerships	$	779			$	86			$	(79	)	$	138		$	(113	)	$	13		$	—		$	824
	Real estate	319				11				(3		)	104			(86		)	12			—			357
	Other investments	202				17				(24		)	11			6			4			—			216
	Insurance group annuity contracts	20				160				(157		)	1			(1		)	—			—			23
	Corporate stocks	8				1				—			—			—			—			—			9
	Corporate obligations	1				—				—			—			—			—			—			1
	Total assets	$	1,329			$	275			$	(263	)	$	254		$	(194	)	$	29		$	—		$	1,430

Stock_Benefit_Plans_Tables

Stock Benefit Plans (Tables)	12 Months Ended
	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]	'
Option pricing valuation model for options granted	'
	The assumptions used in the Black-Scholes option pricing valuation model for options granted by the Company in 2013, 2012 and 2011 are as follows:
		2013		2012		2011
	Risk-free interest rate	1.03%-1.30%		1.26%-1.27%		2.28%-2.90%
	Expected life (in years)	6		6.5		6.75
	Expected volatility	23.6%-24.1%		26.2%-26.4%		25.4%-25.8%
	Expected dividend yield	2.48%-2.54%		2.76%-2.80%		2.75%-2.86%
Summary of the status of MMC's stock option awards	'
	A summary of the status of the Company’s stock option awards as of December 31, 2013 and changes during the year then ended is presented below:
		Shares			Weighted			Weighted		Aggregate
					Average Exercise			Average		Intrinsic Value
					Price			Remaining		$0
								Contractual
								Term
	Balance at January 1, 2013	32,045,793			$	29.1
	Granted	2,563,951			$	36.55
	Exercised	(9,928,320	)		$	28.31
	Forfeited	(124,911	)		$	30.18
	Expired	(1,988,647	)		$	40.46
	Balance at December 31, 2013	22,567,866			$	29.29		4.9 years		$	428,167
	Options vested or expected to vest at December 31, 2013	22,098,993			$	29.26		4.9 years		$	419,912
	Options exercisable at December 31, 2013	15,750,814			$	28.02		3.6 years		$	318,923
Summary of restricted stock units and performance stock units	'
	A summary of the status of the Company's restricted stock units and performance stock units as of December 31, 2013 and changes during the period then ended is presented below:
		Restricted Stock Units					Performance Stock Units
		Shares		Weighted Average			Shares		Weighted Average Grant Date Fair Value
				Grant Date
				Fair Value
	Non-vested balance at January 1, 2013	8,964,238		$	28.58		730,838		$	31.32
	Granted	842,433		$	36.7		289,200		$	36.54
	Vested	(5,310,027	)	$	26.96		(76,844	)	$	31.22
	Forfeited	(245,835	)	$	31.29		(19,412	)	$	32.71
	Adjustment due to performance	—		$	—		37,381		$	31.24
	Non-vested balance at December 31, 2013	4,250,809		$	32.04		961,163		$	32.87
Summary of restricted stock awards activity	'
	A summary of the status of the Company's restricted stock awards as of December 31, 2013 and changes during the period then ended is presented below:
		Shares			Weighted Average
					Grant Date
					Fair Value
	Non-vested balance at January 1, 2013	31,700			$	47.31
	Granted	—			$	—
	Vested	(24,500	)		$	47.66
	Forfeited	—			$	—
	Non-vested balance at December 31, 2013	7,200			$	46.14

Fair_Value_Measurements_Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2013
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 December 31, 2013 and 2012.
	(In millions of dollars)	Identical Assets						Observable Inputs				Unobservable				Total
		(Level 1)						(Level 2)				Inputs
												(Level 3)
		12/31/13			12/31/12			12/31/13		12/31/12		12/31/13		12/31/12		12/31/13		12/31/12
	Assets:
	Financial instruments owned:
	Mutual funds(a)	$	154		$	139		$	—	$	—	$	—	$	—	$	154	$	139
	Money market funds(b)	45			483			—		—		—		—		45		483
	Interest rate swap derivatives(c)	—			—			3		6		—		—		3		6
	Total assets measured at fair value	$	199		$	622		$	3	$	6	$	—	$	—	$	202	$	628
	Fiduciary Assets:
	State and local obligations (including non-U.S. locales)	$	—		$	—		$	—	$	3	$	—	$	—	$	—	$	3
	Money market funds	—			149			—		—		—		—		—		149
	Total fiduciary assets measured at fair value	$	—		$	149		$	—	$	3	$	—	$	—	$	—	$	152
	Liabilities:
	Contingent purchase consideration liability(d)	$	—		$	—		$	—	$	—	$	104	$	63	$	104	$	63
	Senior Notes due 2014(e)	$	—		$	—		$	253	$	256	$	—	$	—	$	253	$	256
	Total liabilities measured at fair value	$	—		$	—		$	253	$	256	$	104	$	63	$	357	$	319
	(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 for the years ended December 31, 2013 and December 31, 2012 that represent contingent purchase consideration related to acquisitions:
	(In millions of dollars)	2013			2012
	Balance at January 1,	$	63		$	110
	Additions	26			27
	Payments	(17		)	(30		)
	Revaluation Impact	32			(44		)
	Balance at December 31,	$	104		$	63

LongTerm_Commitments_Tables

Long-Term Commitments (Tables)	12 Months Ended
	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]	'
Schedule of Future Minimum Rental Payments for Operating Leases	'
	At December 31, 2013, the aggregate future minimum rental commitments under all non-cancelable operating lease agreements are as follows:
	For the Years Ended December 31,	Gross		Rentals		Net
		Rental		from		Rental
	(In millions of dollars)	Commitments		Subleases		Commitments
	2014	$	398	$	52	$	346
	2015	$	357	$	46	$	311
	2016	$	318	$	45	$	273
	2017	$	273	$	42	$	231
	2018	$	244	$	40	$	204
	Subsequent years	$	1,101	$	86	$	1,015
Future Minimum Rental Commitments	'
	At December 31, 2013, the aggregate fixed future minimum commitments under these agreements are as follows:
	For the Years Ended December 31,	Future
		Minimum
	(In millions of dollars)	Commitments
	2014	$	285
	2015	119
	2016	102
	Subsequent years	170
		$	676

Debt_Tables

Debt (Tables)	12 Months Ended
	Dec. 31, 2013
Debt Disclosure [Abstract]	'
Schedule of Outstanding Debt	'
	The Company’s outstanding debt is as follows:
	December 31,
	(In millions of dollars)	2013			2012
	Short-term:
	Current portion of long-term debt	$	334		$	260
	Long-term:
	Senior notes – 4.850% due 2013	—			250
	Senior notes – 5.875% due 2033	297			296
	Senior notes – 5.375% due 2014	323			326
	Senior notes – 5.75% due 2015	230			479
	Senior notes – 2.30% due 2017	249			249
	Senior notes – 9.25% due 2019	399			398
	Senior notes – 4.80% due 2021	497			497
	Senior notes - 2.55% due 2018	248			—
	Senior notes - 4.05% due 2023	247			—
	Mortgage – 5.70% due 2035	413			422
	Term Loan Facility - due 2016	50			—
	Other	2			1
		2,955			2,918
	Less current portion	334			260
		$	2,621		$	2,658
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 periods ended December 31, 2013 and 2012 is as follows:
		2013							2012
	Income statement classification	Loss on			Gain on		Net		Loss on			Gain on		Net
	(In millions of dollars)	Swaps			Notes		Income		Swaps			Notes		Income
							Effect							Effect
	Other Operating Expenses	$	(3	)	$	3	$	—	$	(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.
		December 31, 2013					December 31, 2012
	(In millions of dollars)	Carrying			Fair		Carrying		Fair
		Amount			Value		Amount		Value
	Short-term debt	$	334		$	334	$	260	$	261
	Long-term debt	$	2,621		$	2,819	$	2,658	$	2,986

Integration_and_Restructuring_1

Integration and Restructuring Costs (Tables)	12 Months Ended
	Dec. 31, 2013
Restructuring and Related Activities [Abstract]	'
Restructuring Activities	'
	Details of the restructuring liability activity from January 1, 2012 through December 31, 2013, including actions taken prior to 2013 are as follows:
	(In millions of dollars)	Balance at		Expense		Cash			Other			Balance at		Expense		Cash			Other			Balance at
		1/1/12		Incurred		Paid						12/31/12		Incurred		Paid						12/31/13
	Severance	$	27	$	46	$	(38	)	$	1		$	36	$	9	$	(33	)	$	(1	)	$	11
	Future rent under non-cancelable leases and other costs	154		32		(50		)	(2		)	134		13		(32		)	(2		)	113
	Total	$	181	$	78	$	(88	)	$	(1	)	$	170	$	22	$	(65	)	$	(3	)	$	124

Segment_Information_Tables

Segment Information (Tables)	12 Months Ended
	Dec. 31, 2013
Segment Reporting [Abstract]	'
Selected Information And Details For MMC's Operating Segments	'
	Selected information about the Company’s segments and geographic areas of operation are as follows:
	For the Year Ended December 31, (In millions of dollars)	Revenue				Operating				Total				Depreciation		Capital
						Income				Assets				and		Expenditures
						(Loss)								Amortization
	2013 –
	Risk and Insurance Services	$	6,596		(a)	$	1,421			$	11,365			$	192	$	158
	Consulting	5,701			(b)	845				5,178				115		155
	Total Segments	12,297				2,266				16,543				307		313
	Corporate / Eliminations	(36		)	(c)	(189		)	(c)	437			(d)	51		88
	Total Consolidated	$	12,261			$	2,077			$	16,980			$	358	$	401
	2012 –
	Risk and Insurance Services	$	6,350		(a)	$	1,334			$	9,832			$	196	$	131
	Consulting	5,613			(b)	692				5,203				113		117
	Total Segments	11,963				2,026				15,035				309		248
	Corporate / Eliminations	(39		)	(c)	(197		)	(c)	1,253			(d)	40		72
	Total Consolidated	$	11,924			$	1,829			$	16,288			$	349	$	320
	2011 –
	Risk and Insurance Services	$	6,079		(a)	$	1,200			$	9,102			$	189	$	146
	Consulting	5,487			(b)	617				4,820				112		91
	Total Segments	11,566				1,817				13,922				301		237
	Corporate / Eliminations	(40		)	(c)	(179		)	(c)	1,532			(d)	31		43
	Total Consolidated	$	11,526			$	1,638			$	15,454			$	332	$	280
	(a)	Includes inter-segment revenue of $5 million in both 2013 and 2012 and $4 million in 2011, interest income on fiduciary funds of $27 million, $39 million and $47 million in 2013, 2012 and 2011, respectively, and equity method income of $8 million, $11 million and $14 million in 2013, 2012 and 2011, respectively.
	(b)	Includes inter-segment revenue of $31 million, $34 million and $36 million in 2013, 2012 and 2011, respectively, and interest income on fiduciary funds of $5 million in 2013, and $4 million in both 2012 and 2011.
	(c)	Includes results of corporate advisory and restructuring business.
	(d)	Corporate assets primarily include insurance recoverables, pension related assets, the owned portion of the Company headquarters building and intercompany eliminations.
Details of Operating Segment Revenue	'
	Details of operating segment revenue are as follows:
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Risk and Insurance Services
	Marsh	$	5,461			$	5,265			$	5,031
	Guy Carpenter	1,135				1,085				1,048
	Total Risk and Insurance Services	6,596				6,350				6,079
	Consulting
	Mercer	4,241				4,147				4,004
	Oliver Wyman Group	1,460				1,466				1,483
	Total Consulting	5,701				5,613				5,487
	Total Segments	12,297				11,963				11,566
	Corporate/ Eliminations	(36		)		(39		)		(40		)
	Total	$	12,261			$	11,924			$	11,526
Information by Geographic Area	'
	Information by geographic area is as follows:
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Revenue
	United States	$	5,485			$	5,300			$	5,131
	United Kingdom	1,979				1,960				1,922
	Continental Europe	1,943				1,879				1,906
	Asia Pacific	1,396				1,346				1,287
	Other	1,494				1,478				1,320
		12,297				11,963				11,566
	Corporate/Eliminations	(36		)		(39		)		(40		)
		$	12,261			$	11,924			$	11,526
	For the Years Ended December 31,
	(In millions of dollars)	2013				2012				2011
	Fixed Assets, Net
	United States	$	494			$	494			$	505
	United Kingdom	121				121				133
	Continental Europe	64				63				65
	Asia Pacific	72				62				37
	Other	77				69				64
		$	828			$	809			$	804

Summary_of_Significant_Account3

Summary of Significant Accounting Policies (Narratives) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'	'	'
Number of business segments	2	'	'
Uncollected Premiums and Claims, Net of Related Payables	$8,200,000,000	$9,100,000,000	'
Restricted Cash and Cash Equivalents	190,000,000	'	'
Indefinite-lived intangible assets	0	0	'
Private Equity Funds [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Investment securities	12,000,000	33,000,000	10,000,000
Trident III [Member] | Performance Fees [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Deferred Revenue	38,000,000	63,000,000	'
Recognition of deferred performance fees	40,000,000	'	'
Trident II [Member] | Private Equity Funds [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Proceeds from Equity Method Investment, Dividends or Distributions	100,000,000	'	'
Trident II [Member] | Performance Fees [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Recognition of deferred performance fees	15,000,000	'	'
Mercer Consulting Group [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Assets in trusts or funds for management or trustee fee	16,000,000,000	'	'
Risk and Insurance Services Segment [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Interest Income, Fiduciary Assets	27,000,000	39,000,000	47,000,000
Consulting Segment [Member]	'	'	'
Schedule of Equity Method Investments [Line Items]	'	'	'
Number of business groups	2	'	'
Interest Income, Fiduciary Assets	$5,000,000	$4,000,000	$4,000,000

Summary_of_Significant_Account4

Summary of Significant Accounting Policies (Components of Fixed Assets and Capitalized Software Costs) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

In Millions, unless otherwise specified

Furniture and Fixtures [Member]

Furniture and Fixtures [Member]

Land and Building [Member]

Land and Building [Member]

Leasehold Improvements [Member]

Leasehold Improvements [Member]

Minimum [Member]

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [Member]

Maximum [Member]

Software Development [Member]

Furniture and Fixtures [Member]

Building [Member]

Software Development [Member]

Furniture and Fixtures [Member]

Building [Member]

Property, Plant and Equipment [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Property, plant and equipment, gross

$2,425

$2,391

'

$1,201

$1,168

$408

$412

$816

$811

'

'

'

'

'

'

Less-accumulated depreciation and amortization

-1,597

-1,582

'

'

'

'

'

'

'

'

'

'

'

'

'

Property, plant and equipment, net

828

809

804

'

'

'

'

'

'

'

'

'

'

'

'

Property, plant and equipment, useful life

'

'

'

'

'

'

'

'

'

'3 years

'3 years

'30 years

'10 years

'10 years

'40 years

Capitalized computer software costs

399

278

'

'

'

'

'

'

'

'

'

'

'

'

'

Capitalized computer software costs accumulated amortization

$748

$691

'

'

'

'

'

'

'

'

'

'

'

'

'

Summary_of_Significant_Account5

Summary of Significant Accounting Policies (Basic and Diluted EPS Calculation for Continuing Operations) (Details) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Organization, Consolidation and Presentation of Financial Statements [Abstract]	'	'	'
Net income from continuing operations	$1,379	$1,204	$982
Less: Net income attributable to non-controlling interests	28	25	22
Net income attributable to the Company	$1,351	$1,179	$960
Basic weighted average common shares outstanding (in shares)	549,000,000	544,000,000	542,000,000
Dilutive effect of potentially issuable common shares (in shares)	9,000,000	8,000,000	9,000,000
Dilutive weighted average common shares outstanding (in shares)	558,000,000	552,000,000	551,000,000
Average stock price used to calculate common stock equivalents (in dollars per share)	$40.97	$33.10	$29.40
Stock options outstanding (in shares)	22,567,866	32,045,793	38,900,000

Supplemental_Disclosures_Narra

Supplemental Disclosures (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Cash Flow Information [Abstract]	'	'	'
Non-cash issuance of common stock	$150	$193	$197
Stock-based compensation expense, equity awards	$110	$152	$165

Supplemental_Disclosures_Sched

Supplemental Disclosures (Schedule of Supplemental Cash Flow Disclosures) (Details) (USD $)	3 Months Ended	12 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Supplemental Cash Flow Information [Abstract]	'	'	'	'
Assets acquired, excluding cash	'	$217	$380	$214
Released from escrow in 2012	-62	0	-62	0
Liabilities assumed	'	-53	-42	-21
Contingent/deferred purchase consideration	'	-39	-46	-33
Net cash outflow for current year acquisitions	'	125	230	160
Purchase of other intangibles	'	2	3	4
Deferred purchase consideration from prior years' acquisitions	'	15	59	11
Subtotal	'	142	292	175
Cash paid into escrow for future acquisition	'	0	0	62
Net cash outflow for acquisitions	'	142	292	237
Interest paid	'	170	183	188
Income taxes paid, net of refunds	'	$360	$350	$37

Supplemental_Disclosures_Sched1

Supplemental Disclosures (Schedule of Analysis for Doubtful Accounts) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Allowance for Doubtful Accounts Receivable [Roll Forward]	'	'	'
Balance at beginning of year	$106	$105	$114
Provision charged to operations	16	11	11
Accounts written-off, net of recoveries	-19	-12	-21
Effect of exchange rate changes and other	-5	2	1
Balance at end of year	$98	$106	$105

Other_Comprehensive_Income_Los2

Other Comprehensive Income (Loss) (Schedule Of Components Of Other Comprehensive Income (Loss)) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Equity [Abstract]	'	'	'
Foreign currency translation adjustments, Pre-Tax	($86)	$177	($100)
Foreign currency translation adjustments, Tax Expense	-2	-5	4
Foreign currency translation adjustments, Net of Tax	-84	182	-104
Unrealized investment loss, Pre-Tax	1	-1	-9
Unrealized investment holding losses, net of income tax (credit) expense	0	1	-4
Unrealized investment holding gains (losses),Net of Tax	1	-2	-5
Pension/post-retirement plans:	'	'	'
Prior service gains. Pre-Tax	-22	-31	-32
Prior service cost, Tax Expense	-8	-12	-13
Prior service cost, Net of Tax	-14	-19	-19
Net actuarial losses, Pre-Tax	317	270	213
Net actuarial losses, Tax Expense	108	90	68
Net actuarial losses, Net of Tax	209	180	145
Subtotal, Pre-Tax	295	239	181
Subtotal, Tax Expense	100	78	55
Subtotal, Net of Tax	195	161	126
Net gain (loss) arising during period, Pre-Tax	898	-648	-1,289
Net gain (loss) arising during period, Tax Expense	339	-217	-388
Net gain (loss) arising during period, Net of Tax	559	-431	-901
Foreign currency translation adjustments, Pre-Tax	27	-113	-14
Foreign currency translation adjustments, Tax Expense	8	-26	-3
Foreign currency translation adjustments, Net of Tax	19	-87	-11
Other adjustments. Pre-Tax	-7	75	8
Other adjustments, Tax Expense	-3	17	1
Other adjustments, Net of Tax	-4	58	7
Pension/post-retirement plans gains (losses), Pre-Tax	1,213	-447	-1,114
Pension/post-retirement plans gains (losses), Tax Expense	444	-148	-335
Pension/post-retirement plans gains (losses), Net of Tax	769	-299	-779
Other comprehensive income (loss), before tax	1,128	-271	-1,223
Other comprehensive income (loss), Tax	442	-152	-335
Other comprehensive income (loss), net of tax	$686	($119)	($888)

Other_Comprehensive_Income_Los3

Other Comprehensive Income (Loss) (Components of Accumulated Other Comprehensive Income Loss) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Balance as of January 1, 2013	($3,307)	'	'
Other comprehensive income (loss) before reclassifications	491	'	'
Amounts reclassified from accumulated other comprehensive income	195	'	'
Other comprehensive income (loss), net of tax	686	-119	-888
Balance as of December 31, 2013	-2,621	-3,307	'
Foreign currency translation adjustments (net of deferred tax liability of $7 and $9 in 2013 and 2012, respectively)	56	140	'
Net unrealized investment gains (net of deferred tax liability of $2 in 2013 and 2012, respectively)	5	4	'
Net charges related to pension / post-retirement plans (net of deferred tax asset of $1,213 and $1,657 in 2013 and 2012, respectively)	-2,682	-3,451	'
Accumulated other comprehensive income (loss)	-2,621	-3,307	'
Foreign currency translation adjustments, tax portion	7	9	'
Net unrealized investment gains, tax portion	2	2	'
Net charges related to pension/ retiree plans, tax portion	1,213	1,657	'
Accumulated Net Unrealized Investment Gain (Loss) [Member]	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Balance as of January 1, 2013	4	'	'
Other comprehensive income (loss) before reclassifications	1	'	'
Amounts reclassified from accumulated other comprehensive income	0	'	'
Other comprehensive income (loss), net of tax	1	'	'
Balance as of December 31, 2013	5	'	'
Accumulated other comprehensive income (loss)	5	'	'
Accumulated Defined Benefit Plans Adjustment [Member]	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Balance as of January 1, 2013	-3,451	'	'
Other comprehensive income (loss) before reclassifications	574	'	'
Amounts reclassified from accumulated other comprehensive income	195	'	'
Other comprehensive income (loss), net of tax	769	'	'
Balance as of December 31, 2013	-2,682	'	'
Accumulated other comprehensive income (loss)	-2,682	'	'
Accumulated Translation Adjustment [Member]	'	'	'
Increase (Decrease) in Stockholders' Equity [Roll Forward]	'	'	'
Balance as of January 1, 2013	140	'	'
Other comprehensive income (loss) before reclassifications	-84	'	'
Amounts reclassified from accumulated other comprehensive income	0	'	'
Other comprehensive income (loss), net of tax	-84	'	'
Balance as of December 31, 2013	56	'	'
Accumulated other comprehensive income (loss)	$56	'	'

Acquisitions_Narrative_Details

Acquisitions (Narrative) (Details) (USD $)

3 Months Ended

12 Months Ended

12 Months Ended

In Millions, unless otherwise specified

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Feb. 29, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2012

Dec. 31, 2012

Acquisition Yokogawa-ORC [Member]

Current Fiscal Period Acquisitions [Member]

Prior Fiscal Periods Acquisitions [Member]

Prior Fiscal Periods Acquisitions [Member]

Risk and Insurance Services Segment [Member]

Consulting Segment [Member]

Maximum [Member]

Maximum [Member]

Minimum [Member]

Minimum [Member]

Marsh Insurance Group [Member]

Mercer Consulting Group [Member]

acquisition

acquisition

acquisition

acquisition

Business Acquisition [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of acquisitions made

'

'

'

'

'

'

'

'

6

2

'

'

'

'

12

3

Total Consideration

'

$178

$360

'

'

$178

'

'

'

'

'

'

'

'

'

'

Cash

'

139

252

'

'

139

'

'

'

'

'

'

'

'

'

'

Estimated fair value of deferred/contingent consideration

'

39

46

33

'

39

'

'

'

'

'

'

'

'

'

'

Revenue target period (in years)

'

'

'

'

'

'

'

'

'

'

'4 years

'4 years

'2 years

'2 years

'

'

Deferred purchase consideration from prior years' acquisitions

'

15

59

11

'

'

15

'

'

'

'

'

'

'

'

'

Contingent payments for acquisitions

'

'

'

'

'

'

17

30

'

'

'

'

'

'

'

'

Purchase of other intangibles

'

2

3

4

'

'

'

'

'

'

'

'

'

'

'

'

Business combination remaining interest acquired

'

'

'

'

49.00%

'

'

'

'

'

'

'

'

'

'

'

Cash held in escrow related to acquisition

62

0

62

0

'

'

'

'

'

'

'

'

'

'

'

'

Deferred purchase consideration

'

'

'

'

'

'

'

59

'

'

'

'

'

'

'

'

Revenue related to acquisitions

'

'

'

'

'

50

'

'

'

'

'

'

'

'

'

'

Net operating income related to acquisitions

'

'

'

'

'

$9

'

'

'

'

'

'

'

'

'

'

Acquisitions_Allocation_Of_Acq

Acquisitions (Allocation Of Acquisition Costs) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Business Acquisition [Line Items]	'	'	'
Intangible asset useful life	'10 years	'	'
Cash	$139	$252	'
Estimated fair value of deferred/contingent consideration	39	46	33
Total Consideration	178	360	'
Allocation of purchase price:	'	'	'
Goodwill	6,893	6,792	6,562
Current Fiscal Period Acquisitions [Member]	'	'	'
Business Acquisition [Line Items]	'	'	'
Cash	139	'	'
Estimated fair value of deferred/contingent consideration	39	'	'
Total Consideration	178	'	'
Allocation of purchase price:	'	'	'
Cash and cash equivalents	14	'	'
Accounts receivable, net	10	'	'
Other current assets	12	'	'
Property, plant, and equipment	3	'	'
Intangible assets (primarily customer lists amortized over 10 years)	77	'	'
Goodwill	113	'	'
Other assets	2	'	'
Total assets acquired	231	'	'
Current liabilities	21	'	'
Other liabilities	32	'	'
Total liabilities assumed	53	'	'
Net assets acquired	$178	'	'

Acquisitions_ProForma_Informat

Acquisitions (Pro-Forma Information) (Details) (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Business Combinations [Abstract]	'	'	'
Revenue	$12,424	$12,202	$11,778
Income from continuing operations	1,387	1,222	990
Net income attributable to the Company	$1,365	$1,195	$1,001
Basic net income per share:	'	'	'
Basic net income per share - Continuing operations (in dollars per share)	$2.48	$2.20	$1.78
Basic net income per share - Net income attributable to the Company (in dollars per share)	$2.49	$2.20	$1.84
Diluted net income per share:	'	'	'
Diluted net income per share - Continuing operations (in dollars per share)	$2.44	$2.16	$1.75
Diluted net income per share - Net income attributable to the Company (in dollars per share)	$2.45	$2.16	$1.81

Discontinued_Operations_Narrat

Discontinued Operations (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'
Discontinued operation, settlement of tax audits	$6	($3)	$50
Business Process Outsourcing [Member]	'	'	'
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]	'	'	'
Capitalized software written off	'	'	$17

Discontinued_Operations_Income

Discontinued Operations (Income Statement Data) (Details) (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Discontinued Operations and Disposal Groups [Abstract]	'	'	'
Income (loss) from discontinued operations, net of tax	$0	$0	($17)
Disposals of discontinued operations	-4	-2	25
Income tax (credit) expense	-10	1	-25
Disposals of discontinued operations, net of tax	6	-3	50
Discontinued operations, net of tax	$6	($3)	$33
Discontinued operations, net of tax per share	'	'	'
- Basic (in dollars per share)	$0.01	$0	$0.06
- Diluted (in dollars per share)	$0.01	$0	$0.06

Goodwill_And_Other_Intangibles2

Goodwill And Other Intangibles (Narrative) (Details) (USD $)	12 Months Ended			3 Months Ended		12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2013	Dec. 31, 2013
				Risk and Insurance Services Segment [Member]	Risk and Insurance Services Segment [Member]	Risk and Insurance Services Segment [Member]	Consulting Segment [Member]
Segment Reporting Information [Line Items]	'	'	'	'	'	'	'
Goodwill acquired	$113	$226	'	'	'	$96	$17
Goodwill expected to be tax deductible	7	'	'	'	'	'	'
Goodwill	6,893	6,792	6,562	'	'	4,700	2,200
Intangible asset impairment charge	5	8	0	5	8	'	'
Finite lived assets amortization expense	$72	$72	$65	'	'	'	'

Goodwill_And_Other_Intangibles3

Goodwill And Other Intangibles (Changes In The Carrying Amount Of Goodwill) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
Goodwill [Roll Forward]	'		'
Balance as of January 1, as reported	$6,792		$6,562
Goodwill acquired	113		226
Other adjustments(a)	-12	[1]	4	[1]
Balance at December 31,	$6,893		$6,792
[1]	Reflects increases due to the impact of foreign exchange in both years. 2013 also reflects a reduction due to purchase accounting adjustments.

Goodwill_And_Other_Intangibles4

Goodwill And Other Intangibles (Amortized Intangible Assets) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]	'	'
Gross Cost	$888	$814
Accumulated Amortization	416	345
Net Carrying Amount	$472	$469

Goodwill_And_Other_Intangibles5

Goodwill And Other Intangibles (Estimated Future Aggregate Amortization Expense) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Goodwill and Intangible Assets Disclosure [Abstract]	'	'
2014	$77	'
2015	75	'
2016	68	'
2017	61	'
2018	58	'
Subsequent years	133	'
Net Carrying Amount	$472	$469

Income_Taxes_Narrative_Details

Income Taxes (Narrative) (Details) (USD $)	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Disclosure [Abstract]	'	'	'	'	'	'
Investments in foreign subsidiaries	'	'	$5,200,000,000	'	'	'
Effective tax rate	'	'	30.10%	29.00%	30.10%	'
Valuation allowances	'	-1,000,000	10,000,000	23,000,000	'	'
Valuation allowances, beginning balance	16,000,000	'	-3,000,000	'	'	'
Net Operating Loss Carryforwards	'	'	66.00%	'	'	'
Unrecognized tax benefits that would impact effective tax rate	'	'	71,000,000	96,000,000	102,000,000	'
Accrued interest and penalties	'	'	10,000,000	13,000,000	17,000,000	'
Unrecognized tax benefits minimum	'	'	0	'	'	'
Unrecognized tax benefits maximum	'	'	21,000,000	'	'	'
Tax Credit Carryforward [Line Items]	'	'	'	'	'	'
Putnam and issues included in consolidated mmc tax returns	'	'	128,000,000	117,000,000	143,000,000	199,000,000
State and Local Jurisdiction [Member]	'	'	'	'	'	'
Tax Credit Carryforward [Line Items]	'	'	'	'	'	'
Unrecognized Tax Benefits Resulting in Net Operating Loss Carryforward	'	'	60,000,000	'	'	'
Foreign Tax Authority [Member]	'	'	'	'	'	'
Tax Credit Carryforward [Line Items]	'	'	'	'	'	'
Unrecognized Tax Benefits Resulting in Net Operating Loss Carryforward	'	'	90,000,000	'	'	'
Internal Revenue Service (IRS) [Member]	'	'	'	'	'	'
Tax Credit Carryforward [Line Items]	'	'	'	'	'	'
Domestic deferred tax assets	'	'	195,000,000	'	'	'
Putnam and Kroll [Member]	'	'	'	'	'	'
Tax Credit Carryforward [Line Items]	'	'	'	'	'	'
Putnam and issues included in consolidated mmc tax returns	'	'	$2,000,000	$6,000,000	$14,000,000	'

Income_Taxes_Taxes_on_Income_D

Income Taxes (Taxes on Income) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
U.S., income before income taxes	$407	$398	$121
Other, income before income taxes	1,566	1,298	1,283
Total income before income taxes	1,973	1,696	1,404
U.S. Federal, current	102	42	7
Other national governments, current	264	336	289
U.S. state and local, current	45	24	24
Total current income taxes	411	402	320
U.S. Federal, deferred	12	-18	5
Other national governments, deferred	149	89	90
U.S. state and local, deferred	22	19	7
Total deferred income taxes	183	90	102
Total income taxes	$594	$492	$422

Income_Taxes_Deferred_Income_T

Income Taxes (Deferred Income Tax Assets And Liabilities) (Details) (USD $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Deferred tax assets:	'		'
Accrued expenses not currently deductible	$570		$589
Differences related to non-U.S. operations	140	[1]	159	[1]
Net operating losses	79	[2]	104	[2]
Income currently recognized for tax	74		75
Foreign tax credit carryforwards	157		224
Other	90		77
Total, deferred tax assets	1,407		1,939
Deferred tax liabilities:	'		'
Unrealized investment holding gains	2		2
Differences related to non-U.S. operations	112		107
Depreciation and amortization	273		245
Accrued retirement & postretirement benefits - non-U.S. operations	89		0
Other	3		4
Total, deferred tax liabilities	479		358
Deferred Tax Assets Related To Non U S Operations [Member]	'		'
Deferred tax assets:	'		'
Accrued retirement & postretirement benefits—non-U.S. operations	0		107
Deferred tax liabilities:	'		'
Valuation allowance, amount	12		7
Deferred Tax Assets Related To US Pension [Member]	'		'
Deferred tax assets:	'		'
Accrued retirement & postretirement benefits—non-U.S. operations	297		604
Deferred Tax Assets Related To Net Operating Loss [Member]	'		'
Deferred tax liabilities:	'		'
Valuation allowance, amount	70		65
Current Assets [Member]	'		'
Balance sheet classifications:	'		'
Current assets	482		410
Other Noncurrent Assets [Member]	'		'
Balance sheet classifications:	'		'
Other assets	626		1,223
Other Current Liabilities [Member]	'		'
Balance sheet classifications:	'		'
Current liabilities	-18		-18
Other Noncurrent Liabilities [Member]	'		'
Balance sheet classifications:	'		'
Other liabilities	($162)		($34)
[1]	Net of valuation allowances of $12 million in 2013 and $7 million in 2012.
[2]	Net of valuation allowances of $70 million in 2013 and $65 million in 2012.

Income_Taxes_US_Federal_Statut

Income Taxes (U.S. Federal Statutory Rate) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Tax Disclosure [Abstract]	'	'	'
U.S. Federal statutory rate	35.00%	35.00%	35.00%
U.S. state and local income taxes—net of U.S. Federal income tax benefit	2.10%	1.90%	1.60%
Differences related to non-U.S. operations	-6.00%	-6.10%	-6.50%
Other	-1.00%	-1.80%	0.00%
Effective tax rate	30.10%	29.00%	30.10%

Income_Taxes_Unrecognized_Tax_

Income Taxes (Unrecognized Tax Benefits) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]	'	'	'
Balance at January 1,	$117	$143	$199
Additions, based on tax positions related to current year	16	26	7
Additions for tax positions of prior years	35	35	39
Reductions for tax positions of prior years	-7	-41	-91
Settlements	-3	-6	-6
Lapses in statutes of limitation	-30	-40	-5
Balance at December 31,	$128	$117	$143

Retirement_Benefits_Narrative_

Retirement Benefits (Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

12 Months Ended

3 Months Ended

Share data in Millions, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

Jan. 31, 2014

Mar. 31, 2014

Non Medicare Eligible [Member]

Medicare Eligible [Member]

U.S. Pension Benefits [Member]

U.S. Pension Benefits [Member]

U.S. Pension Benefits [Member]

Non- U.S Pension Benefits [Member]

Non- U.S Pension Benefits [Member]

Non- U.S Pension Benefits [Member]

U.S. Postretirement Benefits [Member]

U.S. Postretirement Benefits [Member]

U.S. Postretirement Benefits [Member]

United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]

Foreign Pension and Postretirement Benefit Plan, Defined Benefit [Member]

Foreign Pension and Postretirement Benefit Plan, Defined Benefit [Member]

United States Nonqualified Pension Plan of US Entity, Defined Benefit [Member]

Equity Funds [Member]

Fixed Income Funds [Member]

United Kingdom [Member]

United Kingdom [Member]

United Kingdom [Member]

United Kingdom [Member]

United Kingdom [Member]

United States [Member]

United States [Member]

United States [Member]

Geographic Concentration Risk [Member]

Trident III [Member]

Subsequent Event [Member]

Scenario, Forecast [Member]

United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]

United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]

Equity Funds [Member]

Fixed Income Funds [Member]

United Kingdom [Member]

United Kingdom [Member]

Non- U.S Pension Benefits [Member]

Subsequent Event [Member]

Foreign Pension and Postretirement Benefit Plan, Defined Benefit [Member]

Foreign Pension and Postretirement Benefit Plan, Defined Benefit [Member]

Foreign Pension and Postretirement Benefit Plan, Defined Benefit [Member]

Equity Funds [Member]

Non- U.S Pension Benefits [Member]

Non- U.S Pension Benefits [Member]

Non- U.S Pension Benefits [Member]

Defined Benefit Plan Disclosure [Line Items]

'

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Market-related plan assets value, recognition period of investment gains and losses

'5 years

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Target asset allocation U.S. Plan, equities, prior period

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58.00%

42.00%

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50.00%

50.00%

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Actual plan asset allocations

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63.00%

37.00%

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49.00%

51.00%

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Target asset allocation percentage for non-U.S. plan assets, U.K. Plans

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82.00%

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Defined benefit plan target allocation percentage of assets equity alternative investments range, minimum

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53.00%

37.00%

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47.00%

47.00%

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Defined benefit plan target allocation percentage of assets equity alternative investments range, maximum

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63.00%

47.00%

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53.00%

53.00%

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The projected benefit obligation with accumulated benefit obligations

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$4,800,000,000

$5,200,000,000

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$1,700,000,000

$1,700,000,000

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Accumulated benefit obligation

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4,800,000,000

5,100,000,000

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1,500,000,000

1,600,000,000

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Aggregate fair value of plan assets

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4,300,000,000

3,900,000,000

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1,300,000,000

1,200,000,000

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Plans with benefit obligations in excess of plan assets, aggregate benefit obligation

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4,800,000,000

5,200,000,000

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1,700,000,000

1,700,000,000

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Plans with benefit obligations in excess of plan assets, aggregate fair value of plan assets

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4,300,000,000

3,900,000,000

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1,300,000,000

1,200,000,000

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Effect of plan amendment on projected benefit obligation

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147,000,000

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Effect of plan amendment on funded status

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137,000,000

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Plan amendment curtailment gain

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63,000,000

Number of shares the U.S. qualified plan holds contributed by the Company

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5.4

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Shares of common stock representing percentage of plan assets

6.00%

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Health care cost trend rate assumed for next fiscal year

5.80%

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7.50%

7.60%

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Ultimate assumed health care cost trend rate

4.85%

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4.50%

4.50%

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Assumed health care cost trend rate

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5.00%

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Estimated future contributions (less than $1 million for U.S. tax-qualified plan)

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1,000,000

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160,000,000

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24,000,000

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Limited partnership interest in private equity fund

13,562,000,000

12,225,000,000

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4,279,000,000

3,936,000,000

3,493,000,000

9,351,000,000

8,312,000,000

7,206,000,000

0

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0

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111,000,000

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Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]

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ESOP invested in MMC common stock

453,000,000

375,000,000

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The cost of defined contribution plans

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$23,000,000

$21,000,000

$20,000,000

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$50,000,000

$50,000,000

$48,000,000

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Retirement_Benefits_Weighted_A

Retirement Benefits (Weighted Average Actuarial Assumptions Utilized) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Pension Plan, Defined Benefit [Member]	'	'
Weighted average assumptions:	'	'
Discount rate (for expense)	4.38%	4.91%
Expected return on plan assets	7.68%	8.03%
Rate of compensation increase (for expense)	2.43%	3.09%
Discount rate (for benefit obligation)	4.82%	4.38%
Rate of compensation increase (for benefit obligation)	2.64%	2.43%
U.S. Pension Benefits [Member]	'	'
Weighted average assumptions:	'	'
Discount rate (for expense)	4.45%	5.15%
Expected return on plan assets	8.75%	8.75%
Rate of compensation increase (for expense)	2.00%	2.00%
Discount rate (for benefit obligation)	5.30%	4.45%
Rate of compensation increase (for benefit obligation)	2.00%	2.00%
Non- U.S Pension Benefits [Member]	'	'
Weighted average assumptions:	'	'
Discount rate (for expense)	4.33%	4.77%
Expected return on plan assets	7.17%	7.68%
Rate of compensation increase (for expense)	2.69%	3.73%
Discount rate (for benefit obligation)	4.55%	4.33%
Rate of compensation increase (for benefit obligation)	2.99%	2.69%
Postretirement Benefits [Member]	'	'
Weighted average assumptions:	'	'
Discount rate (for expense)	4.32%	5.05%
Expected return on plan assets	0.00%	0.00%
Rate of compensation increase (for expense)	0.00%	0.00%
Discount rate (for benefit obligation)	5.03%	4.32%
Rate of compensation increase (for benefit obligation)	0.00%	0.00%
U.S. Postretirement Benefits [Member]	'	'
Weighted average assumptions:	'	'
Discount rate (for expense)	4.25%	5.10%
Expected return on plan assets	0.00%	0.00%
Rate of compensation increase (for expense)	0.00%	0.00%
Discount rate (for benefit obligation)	5.17%	4.25%
Rate of compensation increase (for benefit obligation)	0.00%	0.00%
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'
Weighted average assumptions:	'	'
Discount rate (for expense)	4.45%	4.95%
Expected return on plan assets	0.00%	0.00%
Rate of compensation increase (for expense)	0.00%	0.00%
Discount rate (for benefit obligation)	4.80%	4.45%
Rate of compensation increase (for benefit obligation)	0.00%	0.00%

Retirement_Benefits_Components

Retirement Benefits (Components of the Net Periodic Benefit Cost) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension Plan, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	$252	$240	$226
Interest cost	581	596	609
Expected return on plan assets	-911	-905	-887
Amortization of prior service credit	-22	-19	-19
Recognized actuarial loss (credit)	315	270	215
Net periodic benefit cost	215	182	144
U.S. Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	104	93	83
Interest cost	229	230	231
Expected return on plan assets	-324	-322	-315
Amortization of prior service credit	-16	-16	-16
Recognized actuarial loss (credit)	207	152	100
Net periodic benefit cost	200	137	83
Non- U.S Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	148	147	143
Interest cost	352	366	378
Expected return on plan assets	-587	-583	-572
Amortization of prior service credit	-6	-3	-3
Recognized actuarial loss (credit)	108	118	115
Net periodic benefit cost	15	45	61
Settlement loss	0	1	0
Curtailment credit	0	-1	0
Special termination benefits	0	0	0
Total cost	15	45	61
Postretirement Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	5	5	5
Interest cost	11	13	13
Expected return on plan assets	'	'	'
Amortization of prior service credit	'	-14	-13
Recognized actuarial loss (credit)	2	'	-4
Net periodic benefit cost	18	4	1
U.S. Postretirement Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	3	3	3
Interest cost	7	8	8
Expected return on plan assets	'	'	'
Amortization of prior service credit	'	-13	-13
Recognized actuarial loss (credit)	'	-1	-4
Net periodic benefit cost	10	-3	-6
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Service cost	2	2	2
Interest cost	4	5	5
Expected return on plan assets	'	'	'
Amortization of prior service credit	'	-1	'
Recognized actuarial loss (credit)	2	1	'
Net periodic benefit cost	8	7	7
Settlement loss	0	0	0
Curtailment credit	0	0	0
Special termination benefits	0	0	0
Total cost	$8	$7	$7

Retirement_Benefits_Effects_of

Retirement Benefits (Effects of One Percentage Point Change in Assumed Health Care Cost Trend Rates) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
United States Pension and Postretirement Benefit Plan of US Entity, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Effect on total of service and interest cost components 1 Percentage Point Increase	$0
Effect on total of service and interest cost components 1 Percentage Point Decrease	0
Effect on postretirement benefit obligation 1 Percentage Point Increase	2
Effect on postretirement benefit obligation 1 Percentage Point Decrease	-7
Foreign Pension and Postretirement Benefit Plan, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Effect on total of service and interest cost components 1 Percentage Point Increase	1
Effect on total of service and interest cost components 1 Percentage Point Decrease	-1
Effect on postretirement benefit obligation 1 Percentage Point Increase	10
Effect on postretirement benefit obligation 1 Percentage Point Decrease	($8)

Retirement_Benefits_Schedules_

Retirement Benefits (Schedules Providing Information Concerning MMC's Defined Benefit Pension Plans and Postretirement Benefit Plans) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at end of year	$13,562	$12,225	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Noncurrent assets	979	260	'
Noncurrent liabilities	-1,150	-2,094	'
U.S. Pension Benefits [Member]	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit obligation at beginning of year	5,197	4,533	'
Service cost	104	93	83
Interest cost	229	230	231
Plan combination	36	'	'
Actuarial (gain) loss	-547	522	'
Medicare Part D subsidy	0	0	'
Benefits paid	-192	-181	'
Benefit obligation at end of year	4,827	5,197	4,533
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at beginning of year	3,936	3,493	'
Plan Combination	21	'	'
Actual return on plan assets	488	500	'
Employer/Company contributions	26	124	'
Benefits paid	-192	-181	'
Fair value of plan assets at end of year	4,279	3,936	3,493
Funded status	-548	-1,261	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Current liabilities	-24	-25	'
Noncurrent liabilities	-524	-1,236	'
Net liability recognized in consolidated balance sheet, December 31	-548	-1,261	'
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]	'	'	'
Prior service credit	7	23	'
Net actuarial (loss) gain	-974	-1,887	'
Total recognized accumulated other comprehensive (loss) income, December 31	-967	-1,864	'
Cumulative employer contributions in excess (deficient) of net periodic cost	419	603	'
Net liability recognized in consolidated balance sheet, December 31	-548	-1,261	'
Accumulated benefit obligation at December 31	4,753	5,114	'
U.S. Postretirement Benefits [Member]	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit obligation at beginning of year	176	162	'
Service cost	3	3	3
Interest cost	7	8	8
Actuarial (gain) loss	-15	13	'
Medicare Part D subsidy	1	3	'
Benefits paid	-14	-13	'
Benefit obligation at end of year	158	176	162
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at beginning of year	0	0	'
Actual return on plan assets	0	0	'
Employer/Company contributions	13	10	'
Benefits paid	-14	-13	'
Fair value of plan assets at end of year	0	0	0
Funded status	-158	-176	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Current liabilities	-8	-9	'
Noncurrent liabilities	-150	-167	'
Net liability recognized in consolidated balance sheet, December 31	-158	-176	'
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]	'	'	'
Prior service credit	0	0	'
Net actuarial (loss) gain	13	-2	'
Total recognized accumulated other comprehensive (loss) income, December 31	13	-2	'
Cumulative employer contributions in excess (deficient) of net periodic cost	-171	-174	'
Net liability recognized in consolidated balance sheet, December 31	-158	-176	'
Accumulated benefit obligation at December 31	0	0	'
Non- U.S Pension Benefits [Member]	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit obligation at beginning of year	8,579	7,717	'
Service cost	148	147	143
Interest cost	352	366	378
Employee contributions	11	11	'
Plan combination	0	-71	'
Actuarial (gain) loss	-53	419	'
Effect of Settlement	-2	-11	'
Effect of curtailment	0	-3	'
Benefits paid	-293	-278	'
Foreign Currency Charges	-31	280	'
Other	0	2	'
Benefit obligation at end of year	8,711	8,579	7,717
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at beginning of year	8,312	7,206	'
Actual return on plan assets	698	721	'
Effect of settlement	-2	-11	'
Employer/Company contributions	620	389	'
Employee contributions	11	11	'
Benefits paid	-293	-278	'
Foreign currency changes	5	273	'
Other	0	1	'
Fair value of plan assets at end of year	9,351	8,312	7,206
Funded status	640	-267	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Noncurrent assets	977	258	'
Current liabilities	-5	-6	'
Noncurrent liabilities	-332	-519	'
Net liability recognized in consolidated balance sheet, December 31	640	-267	'
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]	'	'	'
Prior service credit	85	93	'
Net actuarial (loss) gain	-3,010	-3,309	'
Total recognized accumulated other comprehensive (loss) income, December 31	-2,925	-3,216	'
Cumulative employer contributions in excess (deficient) of net periodic cost	3,565	2,949	'
Net liability recognized in consolidated balance sheet, December 31	640	-267	'
Accumulated benefit obligation at December 31	8,413	8,229	'
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'	'
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]	'	'	'
Benefit obligation at beginning of year	107	91	'
Service cost	2	2	2
Interest cost	4	5	5
Employee contributions	0	0	'
Plan combination	0	0	'
Actuarial (gain) loss	-8	10	'
Effect of Settlement	0	0	'
Effect of curtailment	0	-1	'
Benefits paid	-4	-4	'
Foreign Currency Charges	-4	4	'
Other	0	0	'
Benefit obligation at end of year	97	107	91
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]	'	'	'
Fair value of plan assets at beginning of year	0	0	'
Actual return on plan assets	0	0	'
Effect of settlement	0	0	'
Employer/Company contributions	4	4	'
Employee contributions	0	0	'
Benefits paid	-4	-4	'
Foreign currency changes	0	0	'
Other	0	0	'
Fair value of plan assets at end of year	0	0	0
Funded status	-97	-107	'
Defined Benefit Plan, Amounts Recognized in Balance Sheet [Abstract]	'	'	'
Noncurrent assets	0	0	'
Current liabilities	-4	-4	'
Noncurrent liabilities	-93	-103	'
Net liability recognized in consolidated balance sheet, December 31	-97	-107	'
Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), after Tax [Abstract]	'	'	'
Prior service credit	0	0	'
Net actuarial (loss) gain	-16	-27	'
Total recognized accumulated other comprehensive (loss) income, December 31	-16	-27	'
Cumulative employer contributions in excess (deficient) of net periodic cost	-81	-80	'
Net liability recognized in consolidated balance sheet, December 31	-97	-107	'
Accumulated benefit obligation at December 31	$0	$0	'

Retirement_Benefits_Reconcilia

Retirement Benefits (Reconciliation of Prior Service Credit) (Details) (Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
U.S. Pension Benefits [Member]	'	'
Accumulated Other Comprehensive Income (Loss) [Roll Forward]	'	'
Beginning balance	$23	$39
Recognized as component of net periodic benefit credit	-16	-16
Ending balance, December 31	7	23
Non- U.S Pension Benefits [Member]	'	'
Accumulated Other Comprehensive Income (Loss) [Roll Forward]	'	'
Beginning balance	93	23
Recognized as component of net periodic benefit credit	-6	-3
Effect of curtailment	0	-1
Plan amendments	0	71
Exchange rate adjustments	-2	3
Ending balance, December 31	85	93
U.S. Postretirement Benefits [Member]	'	'
Accumulated Other Comprehensive Income (Loss) [Roll Forward]	'	'
Beginning balance	0	13
Recognized as component of net periodic benefit credit	0	-13
Ending balance, December 31	0	0
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'
Accumulated Other Comprehensive Income (Loss) [Roll Forward]	'	'
Beginning balance	0	1
Recognized as component of net periodic benefit credit	0	-1
Effect of curtailment	0	0
Plan amendments	0	0
Exchange rate adjustments	0	0
Ending balance, December 31	$0	$0

Retirement_Benefits_Reconcilia1

Retirement Benefits (Reconciliation of Net Actuarial Loss) (Details) (Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
U.S. Pension Benefits [Member]	'	'
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]	'	'
Beginning balance	($1,887)	($1,695)
Recognized as component of net periodic benefit cost	208	152
Liability experience	541	-522
Asset experience	164	178
Total amount recognized as change in plan assets and benefit obligations	705	-344
Ending balance, December 31	-974	-1,887
Non- U.S Pension Benefits [Member]	'	'
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]	'	'
Beginning balance	-3,309	-3,038
Recognized as component of net periodic benefit cost	108	118
Effect of settlement	0	1
Liability experience	53	-419
Asset experience	111	138
Effect of curtailment	0	3
Total amount recognized as change in plan assets and benefit obligations	164	-278
Exchange rate adjustments	27	-112
Ending balance, December 31	-3,010	-3,309
U.S. Postretirement Benefits [Member]	'	'
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]	'	'
Beginning balance	-2	12
Recognized as component of net periodic benefit cost	0	-1
Liability experience	15	-13
Asset experience	0	0
Total amount recognized as change in plan assets and benefit obligations	15	-13
Ending balance, December 31	13	-2
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'
Reconciliation of unrecognized net actuarial gain loss [Roll Forward]	'	'
Beginning balance	-27	-19
Recognized as component of net periodic benefit cost	2	1
Effect of settlement	0	0
Liability experience	8	-10
Asset experience	0	0
Effect of curtailment	0	1
Total amount recognized as change in plan assets and benefit obligations	8	-9
Exchange rate adjustments	1	0
Ending balance, December 31	($16)	($27)

Retirement_Benefits_Schedule_o

Retirement Benefits (Schedule of Total Recognized in Net Periodic Benefit Cost and Other Comprehensive Income (Loss) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
U.S. Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Total recognized in net periodic benefit cost and other comprehensive loss (income)	($696)	$346	$467
Non- U.S Pension Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Total recognized in net periodic benefit cost and other comprehensive loss (income)	-276	246	792
U.S. Postretirement Benefits [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Total recognized in net periodic benefit cost and other comprehensive loss (income)	-5	24	-9
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'	'
Total recognized in net periodic benefit cost and other comprehensive loss (income)	($2)	$16	$12

Retirement_Benefits_Schedule_o1

Retirement Benefits (Schedule of Estimated Amounts That Will Be Amortized from Accumulated Other Comprehensive in the Next Fiscal Year) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013
U.S. Pension Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Prior service credit	($7)
Net actuarial loss	105
Projected cost	98
Non- U.S Pension Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Prior service credit	-6
Net actuarial loss	95
Projected cost	89
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Prior service credit	0
Net actuarial loss	1
Projected cost	1
U.S. Postretirement Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
Prior service credit	0
Net actuarial loss	1
Projected cost	$1

Retirement_Benefits_Schedule_o2

Retirement Benefits (Schedule of Estimated Future Benefit Payments for Pension and Postretirement Benefits) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
U.S. Pension Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	$207
2015	219
2016	233
2017	244
2018	255
2019-2023	1,424
Non- U.S Pension Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	287
2015	299
2016	318
2017	342
2018	350
2019-2023	2,046
U.S. Postretirement Benefits [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	11
2015	11
2016	11
2017	11
2018	11
2019-2023	57
Foreign Postretirement Benefit Plan, Defined Benefit [Member]	'
Defined Benefit Plan Disclosure [Line Items]	'
2014	4
2015	4
2016	5
2017	5
2018	5
2019-2023	$27

Retirement_Benefits_Summary_of

Retirement Benefits (Summary of the U.S. and Non-U.S. Plan Investments Measured At Fair Value on a Recurring Basis) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	$13,562,000,000	$12,225,000,000
Transfers from Level 1 to Level 2	0	0
Transfers from Level 2 to Level 1	0	0
Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	3,702,000,000	2,740,000,000
Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	8,353,000,000	8,055,000,000
Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	1,507,000,000	1,430,000,000
Common/Collective trusts [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	5,938,000,000	5,392,000,000
Common/Collective trusts [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	138,000,000	16,000,000
Common/Collective trusts [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	5,649,000,000	5,376,000,000
Common/Collective trusts [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	151,000,000	0
Corporate Obligations [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,334,000,000	2,237,000,000
Corporate Obligations [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Corporate Obligations [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,330,000,000	2,236,000,000
Corporate Obligations [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	4,000,000	1,000,000
Corporate stocks [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,440,000,000	2,018,000,000
Corporate stocks [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,434,000,000	2,005,000,000
Corporate stocks [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	5,000,000	4,000,000
Corporate stocks [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	1,000,000	9,000,000
Private equity/partnerships [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	801,000,000	828,000,000
Private equity/partnerships [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	2,000,000
Private equity/partnerships [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,000,000	2,000,000
Private equity/partnerships [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	799,000,000	824,000,000
Government Securities [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	352,000,000	318,000,000
Government Securities [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	10,000,000	9,000,000
Government Securities [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	340,000,000	309,000,000
Government Securities [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,000,000	0
Real Estate [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	319,000,000	376,000,000
Real Estate [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	11,000,000
Real Estate [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	7,000,000	8,000,000
Real Estate [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	312,000,000	357,000,000
Short-term investment funds [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	839,000,000	414,000,000
Short-term investment funds [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	824,000,000	410,000,000
Short-term investment funds [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	15,000,000	4,000,000
Short-term investment funds [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Company common stock [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	261,000,000	276,000,000
Company common stock [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	261,000,000	276,000,000
Company common stock [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Company common stock [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Other Investments [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	276,000,000	339,000,000
Other Investments [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	35,000,000	11,000,000
Other Investments [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	3,000,000	112,000,000
Other Investments [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	238,000,000	216,000,000
Insurance Group Annuity Contracts [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	23,000,000
Insurance Group Annuity Contracts [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Insurance Group Annuity Contracts [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Insurance Group Annuity Contracts [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	23,000,000
Swaps [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,000,000	4,000,000
Swaps [Member] | Identical Assets (Level 1) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	0	0
Swaps [Member] | Observable Inputs (Level 2) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	2,000,000	4,000,000
Swaps [Member] | Unobservable Inputs (Level 3) [Member]	'	'
Defined Benefit Plan Disclosure [Line Items]	'	'
Fair value of plan assets	$0	$0

Retirement_Benefits_Summary_of1

Retirement Benefits (Summary of changes in the fair value of the plans’ Level 3 assets) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	$1,430	$1,329
Purchases	247	275
Sales	-282	-263
Unrealized Gain/(Loss)	-144	254
Realized Gain/(Loss)	176	-194
Exchange Rate Impact	-3	29
Transfers in/(out) and Other	83	0
Fair Value, Asset Value, Ending	1,507	1,430
Private equity/partnerships [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	824	779
Purchases	146	86
Sales	-174	-79
Unrealized Gain/(Loss)	-155	138
Realized Gain/(Loss)	150	-113
Exchange Rate Impact	-1	13
Transfers in/(out) and Other	9	0
Fair Value, Asset Value, Ending	799	824
Real Estate [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	357	319
Purchases	21	11
Sales	-95	-3
Unrealized Gain/(Loss)	6	104
Realized Gain/(Loss)	26	-86
Exchange Rate Impact	-3	12
Transfers in/(out) and Other	0	0
Fair Value, Asset Value, Ending	312	357
Other Investments [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	216	202
Purchases	18	17
Sales	-13	-24
Unrealized Gain/(Loss)	11	11
Realized Gain/(Loss)	0	6
Exchange Rate Impact	6	4
Transfers in/(out) and Other	0	0
Fair Value, Asset Value, Ending	238	216
Common/Collective trusts [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	0	'
Purchases	61	'
Sales	0	'
Unrealized Gain/(Loss)	-4	'
Realized Gain/(Loss)	0	'
Exchange Rate Impact	-5	'
Transfers in/(out) and Other	99	'
Fair Value, Asset Value, Ending	151	'
Insurance Group Annuity Contracts [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	23	20
Purchases	0	160
Sales	0	-157
Unrealized Gain/(Loss)	-1	1
Realized Gain/(Loss)	0	-1
Exchange Rate Impact	0	0
Transfers in/(out) and Other	-22	0
Fair Value, Asset Value, Ending	0	23
Corporate stocks [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	9	8
Purchases	0	1
Sales	0	0
Unrealized Gain/(Loss)	0	0
Realized Gain/(Loss)	0	0
Exchange Rate Impact	0	0
Transfers in/(out) and Other	-8	0
Fair Value, Asset Value, Ending	1	9
Corporate Obligations [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	1	1
Purchases	1	0
Sales	0	0
Unrealized Gain/(Loss)	0	0
Realized Gain/(Loss)	0	0
Exchange Rate Impact	0	0
Transfers in/(out) and Other	2	0
Fair Value, Asset Value, Ending	4	1
Government Securities [Member]	'	'
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Fair Value, Asset Value, Beginning	0	'
Purchases	0	'
Sales	0	'
Unrealized Gain/(Loss)	-1	'
Realized Gain/(Loss)	0	'
Exchange Rate Impact	0	'
Transfers in/(out) and Other	3	'
Fair Value, Asset Value, Ending	$2	'

Stock_Benefit_Plans_Narrative_

Stock Benefit Plans (Narrative) (Details) (USD $)

12 Months Ended

1 Months Ended

12 Months Ended

12 Months Ended

1 Months Ended

12 Months Ended

In Millions, except Share data, unless otherwise specified

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Feb. 29, 2012

Feb. 28, 2011

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Dec. 31, 2013

Dec. 31, 2013

19-May-11

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

31-May-07

Jul. 31, 2002

Dec. 31, 2013

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock [Member]

Restricted Stock Units And Performance Stock Units [Member]

Restricted Stock Units And Performance Stock Units [Member]

Restricted Stock Units And Performance Stock Units [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Restricted Stock Units (RSUs) [Member]

Performance Shares [Member]

Performance Shares [Member]

Performance Shares [Member]

Performance Shares [Member]

Performance Shares [Member]

Stock Options [Member]

Restricted Stock Units, Restricted Stock and Performance Units [Member]

Award Plans 2000 [Member]

Incentive and Stock Award Plan 2011 [Member]

Incentive and Stock Award Plan 2011 [Member]

Previous Equity Incentive Plans [Member]

Employee Stock Purchase Plan 1999 [Member]

International Plan [Member]

International Plan [Member]

International Plan [Member]

Shares granted prior to 2004 [Member]

Shares granted during 2004 [Member]

Shares granted during 2005 [Member]

Certain grants in 2005 [Member]

equity_incentive_plan

Stock Options [Member]

Stock Options [Member]

Employee Stock [Member]

Employee Stock [Member]

Employee Stock [Member]

Employee Stock [Member]

share_purchase_times

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Number of previous equity plans replaced

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

2

'

'

'

'

'

'

'

Awards authorized (not more than 23.2 million shares for the 2011 Plan and 35.6 million shares for the 1999 Plan)

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

23,200,000

'

'

35,600,000

'

'

12,000,000

Stock options vesting percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

25.00%

25.00%

'

'

'

'

Contractual term of stock option awards

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

'

Stock appreciation percentage above exercise price

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

15.00%

'

'

'

'

Daily closing price observation period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

Average Volatility Periods Ending On Fifteen Anniversaries Prior To Valuation Date

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'10 years

'

'

'

'

'

'

'

'

'

Options, weighted-average grant-date fair value (in dollars per share)

$6.21

$6.04

$6.67

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Total intrinsic value of options exercised

$198.10

$57.70

$23.60

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Unrecognized compensation cost related to option awards

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

17

'

'

'

'

'

'

'

'

'

Weighted-average period over which that cost is expected to be recognized, years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'1 year 2 months 12 days

'1 year

'

'

'

'

'

'

'

'

Cash received from the exercise of stock options

281.1

179.3

111.7

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Vesting period, years

'

'

'

'

'

'10 years

'7 years

'5 years

'3 years

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Performance-based restricted stock unit payable range minimum

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0.00%

'

'

'

'

'

'

'

'

'

'

'

'

Performance-based restricted stock unit payable range maximum

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

200.00%

'

'

'

'

'

'

'

'

'

'

'

'

Performance period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'3 years

'

'

'

'

'

'

'

'

'

'

'

'

Weighted-average grant-date fair value (in dollars per share)

'

'

'

$0

'

'

'

'

'

'

'

'

$36.70

$31.96

$30.46

'

'

$36.54

$31.89

$30.60

'

'

'

'

'

'

'

'

'

'

Total fair value of deferred stock units

'

'

'

1.1

0.6

'

'

'

'

205.5

262.6

249

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Above-target payout percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

200.00%

190.00%

'

'

'

'

'

'

'

'

'

'

'

'

'

Target payout percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

100.00%

'

'

'

'

'

'

'

'

'

'

'

'

Unrecognized compensation cost

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

$73.60

'

'

'

'

'

'

'

'

Number of share purchase times per plan year

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4

'

'

'

Stock option price percent

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

95.00%

'

'

'

Reduction in the shares available

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

10,000,000

'

'

'

Shares purchased by employees

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

748,842

'

'

98,863

Shares available for issuance under the plan

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3,387,471

'

'

2,987,099

Shares due to shareholder action

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

4,000,000

5,000,000

'

Fair value assumptions, volatility rate, period before valuation date for traded options

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'7 days

'

'

'

'

'

'

'

'

'

Stock_Benefit_Plans_BlackSchol

Stock Benefit Plans (Black-Scholes Option Pricing Valuation Model For Options) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Risk-free interest rate, Range Minimum	1.03%	1.26%	2.28%
Risk-free interest rate, Range Maximum	1.30%	1.27%	2.90%
Expected life (in years)	'6 years	'6 years 6 months	'6 years 9 months
Expected volatility, Range Minimum	23.60%	26.20%	25.40%
Expected volatility, Range Maximum	24.10%	26.40%	25.80%
Minimum [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected dividend yield	2.48%	2.76%	2.75%
Maximum [Member]	'	'	'
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]	'	'	'
Expected dividend yield	2.54%	2.80%	2.86%

Stock_Benefit_Plans_The_Status

Stock Benefit Plans (The Status Of Stock Option Awards) (Details) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2011
Options, Outstanding [Roll Forward]	'	'
Number of options outstanding at January 1, 2013 (in shares)	32,045,793	38,900,000
Number of Options Granted (in shares)	2,563,951	'
Number of Options Exercised (in shares)	-9,928,320	'
Number of Options Forfeited (in shares)	-124,911	'
Number of options Expired (in shares)	-1,988,647	'
Number of options outstanding at December, 31 2013 (in shares)	22,567,866	38,900,000
Options vested or expected to vest at December 31, 2013 (in shares)	22,098,993	'
Options exercisable at December 31, 2013 (in shares)	15,750,814	'
Options, Outstanding, Weighted Average Exercise Price [Roll Forward]	'	'
Weighted Average Exercise Price per option at January 1, 2013	$29.10	'
Weighted Average Exercise Price per option Granted	$36.55	'
Weighted Average Exercise Price per option Exercised	$28.31	'
Weighted Average Exercise Price per Option Forfeited	$30.18	'
Weighted Average Exercise Price per Option Expired	$40.46	'
Weighted Average Exercise Price per option at December 31, 2013	$29.29	'
Weighted Average Exercise Price per option expected to vest	$29.26	'
Weighted Average Exercise Price per option exercisable at closing	$28.02	'
Weighted Average Remaining Contractual Term at closing, years	'4 years 10 months 24 days	'
Weighted Average Remaining Contractual Term expected to vest, years	'4 years 10 months 24 days	'
Weighted Average Remaining Contractual Term exercisable at closing, years	'3 years 7 months 6 days	'
Aggregate Intrinsic Value at closing	$428,167	'
Aggregate Intrinsic Value expected to vest	419,912	'
Aggregate Intrinsic Value exercisable at closing	$318,923	'

Stock_Benefit_Plans_Summary_Of

Stock Benefit Plans (Summary Of The Status Of Restricted Stock Unit And Performance Unit Awards) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Restricted Stock Units (RSUs) [Member]	'	'	'
Restricted Stock Units and Performance Stock Units [Roll Forward]	'	'	'
Non-vested balance at January 1, 2013 (in shares)	8,964,238	'	'
Granted (in shares)	842,433	'	'
Vested (in shares)	-5,310,027	'	'
Forfeited (in shares)	-245,835	'	'
Adjustment due to performance (in shares)	0	'	'
Non-vested balance at December 31, 2013 (in shares)	4,250,809	8,964,238	'
Weighted Average Grant Date Fair Value [Roll Forward]	'	'	'
Non-vested balance at January 1, 2013 (in dollars per share)	$28.58	'	'
Granted (in dollars per share)	$36.70	$31.96	$30.46
Vested (in dollars per share)	$26.96	'	'
Forfeited (in dollars per share)	$31.29	'	'
Adjustment due to performance (in dollars per share)	$0	'	'
Non-vested balance at December 31, 2013 (in dollars per share)	$32.04	$28.58	'
Performance Shares [Member]	'	'	'
Restricted Stock Units and Performance Stock Units [Roll Forward]	'	'	'
Non-vested balance at January 1, 2013 (in shares)	730,838	'	'
Granted (in shares)	289,200	'	'
Vested (in shares)	-76,844	'	'
Forfeited (in shares)	-19,412	'	'
Adjustment due to performance (in shares)	37,381	'	'
Non-vested balance at December 31, 2013 (in shares)	961,163	730,838	'
Weighted Average Grant Date Fair Value [Roll Forward]	'	'	'
Non-vested balance at January 1, 2013 (in dollars per share)	$31.32	'	'
Granted (in dollars per share)	$36.54	$31.89	$30.60
Vested (in dollars per share)	$31.22	'	'
Forfeited (in dollars per share)	$32.71	'	'
Adjustment due to performance (in dollars per share)	$31.24	'	'
Non-vested balance at December 31, 2013 (in dollars per share)	$32.87	$31.32	'

Stock_Benefit_Plans_Status_Of_

Stock Benefit Plans (Status Of Restricted Stock Awards) (Details) (Restricted Stock [Member], USD $)	12 Months Ended
	Dec. 31, 2013
Restricted Stock [Member]	'
Restricted Stock [Roll Forward]	'
Non-vested balance at January 1, 2013 (in shares)	31,700
Granted (in shares)	0
Vested (in shares)	-24,500
Forfeited (in shares)	0
Non-vested balance at December 31, 2013 (in shares)	7,200
Weighted Average Grant Date Fair Value [Roll Forward]	'
Non-vested balance at January 1, 2013 (in dollars per share)	$47.31
Granted (in dollars per share)	$0
Vested (in dollars per share)	$47.66
Forfeited (in dollars per share)	$0
Non-vested balance at December 31, 2013 (in dollars per share)	$46.14

Fair_Value_Measurements_Narrat

Fair Value Measurements (Narrative) (Details) (USD $)

12 Months Ended

12 Months Ended

Dec. 31, 2013

Mar. 31, 2011

Feb. 28, 2011

Dec. 31, 2013

Feb. 28, 2011

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

interest_rate_swap

interest_rate_swap

Senior Debt Obligations Due 2014 [Member]

Senior Debt Obligations Due 2014 [Member]

Interest Rate Swap [Member]

Minimum [Member]

Minimum [Member]

Maximum [Member]

Maximum [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 measurement on senior notes subject to interest rate swaps

'

'

'

$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

'2 years

'4 years

'4 years

'

'

Assets transferred between Level 1 and Level 2

0

'

'

'

'

'

'

'

'

'

'

'

Assets transferred between Level 2 To Level 3

0

'

'

'

'

'

'

'

'

'

'

'

Adjustments to acquisition related contingent consideration liability

32,000,000

'

'

'

'

'

'

'

'

'

'

'

Increase in fair value of contingent consideration due to 5% increase in projections

8,000,000

'

'

'

'

'

'

'

'

'

'

'

Decrease in fair value of contingent consideration due to 5% decrease in projections

9,000,000

'

'

'

'

'

'

'

'

'

'

'

Long-term Investments

'

'

'

'

'

'

'

'

'

'

$14,000,000

$16,000,000

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 $)	Dec. 31, 2013		Dec. 31, 2012
In Millions, unless otherwise specified
Financial instruments owned:	'		'
Assets, Fair Value Disclosure	$202		$628
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		152
Liabilities:	'		'
Financial and Nonfinancial Liabilities, Fair Value Disclosure	357		319
Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Assets, Fair Value Disclosure	199		622
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		149
Observable Inputs (Level 2) [Member]	'		'
Financial instruments owned:	'		'
Assets, Fair Value Disclosure	3		6
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		3
Liabilities:	'		'
Financial and Nonfinancial Liabilities, Fair Value Disclosure	253		256
Unobservable Inputs (Level 3) [Member]	'		'
Liabilities:	'		'
Financial and Nonfinancial Liabilities, Fair Value Disclosure	104		63
Other Assets [Member]	'		'
Financial instruments owned:	'		'
Other Assets, Fair Value Disclosure	154	[1]	139	[1]
Other Assets [Member] | Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Other Assets, Fair Value Disclosure	154	[1]	139	[1]
Cash and Cash Equivalents [Member]	'		'
Financial instruments owned:	'		'
Cash and Cash Equivalents, Fair Value Disclosure	45	[2]	483	[2]
Cash and Cash Equivalents [Member] | Identical Assets (Level 1) [Member]	'		'
Financial instruments owned:	'		'
Cash and Cash Equivalents, Fair Value Disclosure	45	[2]	483	[2]
Other Receivables [Member]	'		'
Financial instruments owned:	'		'
Interest rate swap derivatives	3	[3]	6
Other Receivables [Member] | Observable Inputs (Level 2) [Member]	'		'
Financial instruments owned:	'		'
Interest rate swap derivatives	3	[3]	6	[3]
Accounts Payable and Accrued Liabilities and Other Liabilities [Member]	'		'
Liabilities:	'		'
Contingent purchase consideration liability, Fair Value Disclosure	104	[4]	63	[4]
Accounts Payable and Accrued Liabilities and Other Liabilities [Member] | Unobservable Inputs (Level 3) [Member]	'		'
Liabilities:	'		'
Contingent purchase consideration liability, Fair Value Disclosure	104	[4]	63	[4]
US States and US and Foreign Local Debt Securities [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		3
US States and US and Foreign Local Debt Securities [Member] | Observable Inputs (Level 2) [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		3
Money Market Funds [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		149
Money Market Funds [Member] | Identical Assets (Level 1) [Member]	'		'
Fiduciary Assets:	'		'
Fiduciary Assets, Fair Value Disclosure	0		149
Senior Debt Obligations Due 2014 [Member] | Long-term Debt [Member]	'		'
Liabilities:	'		'
Debt Instrument, Fair Value Disclosure	253	[5]	256	[5]
Senior Debt Obligations Due 2014 [Member] | Long-term Debt [Member] | Observable Inputs (Level 2) [Member]	'		'
Liabilities:	'		'
Debt Instrument, Fair Value Disclosure	$253	[5]	$256	[5]
[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 $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Contingent Consideration [Member]	'	'
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]	'	'
Balance at January 1,	$63	$110
Additions	26	27
Payments	-17	-30
Revaluation Impact	32	-44
Balance at December 31,	$104	$63

LongTerm_Commitments_Narrative

Long-Term Commitments (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Commitments and Contingencies Disclosure [Abstract]	'	'	'
Net rental costs	$403	$416	$430
Rentals from subleases	$13	$10	$9
Office Building [Member] | Lease Concentration Risk [Member] | Lease Obligations [Member]	'	'	'
Concentration Risk [Line Items]	'	'	'
Lease obligations for office space	98.00%	'	'

Longterm_Commitments_Operating

Long-term Commitments (Operating Lease Agreements) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Gross Rental Commitments	'
2014, Net Rental Commitments	$398
2015, Gross Rental Commitments	357
2016, Gross Rental Commitments	318
2017, Gross Rental Commitments	273
2018, Gross Rental Commitments	244
Subsequent years, Gross Rental Commitments	1,101
Rental from Subleases	'
2014, Rentals from Subleases	52
2015, Rentals from Subleases	46
2016, Rentals from Subleases	45
2017, Rentals from Subleases	42
2018, Rentals from Subleases	40
Subsequent years, Rentals from Subleases	86
Net Rental Commitments	'
2014, Net Rental Commitments	346
2015, Net Rental Commitments	311
2016, Net Rental Commitments	273
2017, Net Rental Commitments	231
2018, Net Rental Commitments	204
Subsequent years, Net Rental Commitments	$1,015

Longterm_Commitments_Future_Mi

Long-term Commitments (Future Minimum Commitments) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Commitments and Contingencies Disclosure [Abstract]	'
2014	$285
2015	119
2016	102
Subsequent years	170
Total	$676

Debt_Narrative_Details

Debt (Narrative) (Details) (USD $)

1 Months Ended

9 Months Ended

12 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

1 Months Ended

3 Months Ended

1 Months Ended

1 Months Ended

9 Months Ended

Feb. 28, 2011

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2011

Feb. 28, 2012

Mar. 31, 2011

Sep. 30, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2013

Feb. 28, 2011

Mar. 31, 2012

Dec. 31, 2013

Mar. 31, 2012

Dec. 31, 2012

Dec. 31, 2013

Sep. 30, 2013

Sep. 30, 2013

Dec. 31, 2013

Mar. 31, 2012

Oct. 31, 2013

Sep. 30, 2013

Feb. 28, 2013

Feb. 28, 2011

Sep. 30, 2013

Feb. 28, 2011

interest_rate_swap

interest_rate_swap

Senior Debt Obligations Due 2018 [Member]

Senior Debt Obligations Due 2018 [Member]

Other Debt Facilities [Member]

Other Debt Facilities [Member]

Senior Debt Obligations Due 2021 [Member]

Revolving Credit Facility [Member]

Senior Debt Obligations Due 2013 [Member]

Senior Debt Obligations Due 2015 [Member]

Senior Debt Obligations Due 2015 [Member]

Senior Debt Obligations Due 2014 [Member]

Senior Debt Obligations Due 2014 [Member]

Senior Debt Obligations Due 2017 [Member]

Senior Debt Obligations Due 2017 [Member]

Senior Debt Obligations Due 2012 [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Senior Debt Obligations Due 2023 [Member]

Senior Debt Obligations Due 2023 [Member]

Senior Debt Obligations Due 2012 [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]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt instrument, amount

'

'

'

'

'

'

'

$250,000,000

'

'

'

'

'

'

'

'

'

'

$250,000,000

'

'

'

'

'

$250,000,000

'

'

'

'

'

'

'

'

Interest rate

'

'

'

'

'

'

'

2.55%

2.55%

'

'

4.80%

'

4.85%

5.75%

5.75%

5.38%

5.38%

2.30%

2.30%

6.25%

'

'

'

4.05%

4.05%

'

'

'

4.85%

'

'

'

Debt instrument, term

'

'

'

'

'

'

'

'5 years

'

'

'

'

'

'

'

'

'

'

'5 years

'

'

'3 years

'

'

'10 years

'

'

'

'

'

'

'

'

Partial redemption of notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

'

'

'

'

Repayments of long-term debt

'

'

260,000,000

259,000,000

11,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

275,000,000

'

'

'

'

'

Cost for early redemption

'

'

-24,000,000

0

-72,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

-24,000,000

'

'

'

'

'

Revised Purchase Price Allocation For Principal Amount Outstanding of Notes

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

250,000,000

'

'

250,000,000

'

'

'

Revolving credit facility, borrowing capacity

'

'

'

'

'

'

'

'

'

'

'

'

1,000,000,000

'

'

'

'

'

'

'

'

50,000,000

'

'

'

'

'

'

'

'

'

'

'

Revolving credit facility, amount outstanding

'

'

'

'

'

'

'

'

'

1,000,000

0

'

0

'

'

'

'

'

'

'

'

'

50,000,000

'

'

'

'

'

'

'

'

'

'

Line of Credit Facility, Interest Rate at Period End

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

1.29%

'

'

'

'

'

'

'

'

'

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

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Derivative, Fixed Interest Rate

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

5.38%

Floating rate three-month LIBOR plus fixed spread interest percentage

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

3.73%

'

'

Derivative Instrument, Net Settlement Period

'

'6 months

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate swaps, fair value adjustment

'

'

'

'

'

0

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Swap agreements, effectiveness recognized during the period

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

0

'

Debt instrument, unused borrowing capacity

'

'

'

'

'

'

'

'

'

$282,000,000

$247,000,000

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Debt_Schedule_Of_Outstanding_D

Debt (Schedule Of Outstanding Debt) (Details) (USD $)

Dec. 31, 2013

Dec. 31, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Feb. 28, 2011

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Mar. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2013

Sep. 30, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

Dec. 31, 2013

Dec. 31, 2012

In Millions, unless otherwise specified

Senior Debt Obligations Due 2012 [Member]

Senior Debt Obligations Due 2013 [Member]

Senior Debt Obligations Due 2013 [Member]

Senior Debt Obligations Due 2033 [Member]

Senior Debt Obligations Due 2033 [Member]

Senior Debt Obligations Due 2014 [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 2015 [Member]

Senior Debt Obligations Due 2017 [Member]

Senior Debt Obligations Due 2017 [Member]

Senior Debt Obligations Due 2017 [Member]

Senior Debt Obligations Due 2019 [Member]

Senior Debt Obligations Due 2019 [Member]

Senior Debt Obligations Due 2021 [Member]

Senior Debt Obligations Due 2021 [Member]

Senior Debt Obligations Due 2018 [Member]

Senior Debt Obligations Due 2018 [Member]

Senior Debt Obligations Due 2018 [Member]

Senior Debt Obligations Due 2023 [Member]

Senior Debt Obligations Due 2023 [Member]

Senior Debt Obligations Due 2023 [Member]

Mortgage Due 2035 [Member]

Mortgage Due 2035 [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Three-Year Delayed Draw Term Loan Facility [Member]

Other Debt Instruments [Member]

Other Debt Instruments [Member]

Debt Instrument [Line Items]

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Current portion of long-term debt

$334

$260

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Long-term debt, current and noncurrent

2,955

2,918

'

0

250

297

296

323

326

'

230

'

479

249

249

'

399

398

497

497

248

'

0

247

'

0

413

422

50

0

2

1

Long-term debt and capital lease obligations

$2,621

$2,658

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

'

Interest rate

'

'

6.25%

4.85%

'

5.88%

'

5.38%

'

5.38%

5.75%

5.75%

'

2.30%

'

2.30%

9.25%

'

4.80%

'

2.55%

2.55%

'

4.05%

4.05%

'

5.70%

'

'

'

'

'

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 $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Gain on Notes	$3	$1
Other operating expenses net income effect	0	0
Interest Rate Swap [Member]	'	'
Derivative Instruments, Gain (Loss) [Line Items]	'	'
Loss on Swaps	($3)	($1)

Debt_Scheduled_Repayments_Deta

Debt (Scheduled Repayments) (Details) (USD $)	Dec. 31, 2013
In Millions, unless otherwise specified
Maturities of Long-term Debt [Abstract]	'
Repayments of principal in 2014	$331
Repayments of principal in 2015	241
Repayments of principal in 2016	61
Repayments of principal in 2017	262
Repayments of principal in 2018	$262

Debt_Estimated_Fair_Value_Of_S

Debt (Estimated Fair Value Of Significant Financial Instruments) (Details) (USD $)	Dec. 31, 2013	Dec. 31, 2012
In Millions, unless otherwise specified
Reported Value Measurement [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Short-term debt	$334	$260
Long-term debt	2,621	2,658
Estimate of Fair Value Measurement [Member]	'	'
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]	'	'
Short-term debt	334	261
Long-term debt	$2,819	$2,986

Integration_and_Restructuring_2

Integration and Restructuring Costs (Narrative) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Restructuring Cost and Reserve [Line Items]	'	'	'	'
Restructuring actions costs	$22	$78	$51	'
Liability balance	124	170	181	211
Payments for restructuring	65	88	82	'
Risk and Insurance Services Segment [Member] | Acquisition Related [Member]	'	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'	'
Restructuring actions costs	7	'	'	'
Consulting Segment [Member] | Acquisition Related [Member]	'	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'	'
Restructuring actions costs	2	'	'	'
Corporate Segment [Member] | Acquisition Related [Member]	'	'	'	'
Restructuring Cost and Reserve [Line Items]	'	'	'	'
Restructuring actions costs	$13	'	'	'

Integration_and_Restructuring_3

Integration and Restructuring Costs (Restructuring Activities) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Restructuring Reserve [Roll Forward]	'	'	'
Liability at beginning of period	$170	$181	$211
Amounts Accrued	22	78	51
Cash Paid	-65	-88	-82
Other	-3	-1	'
Liability at end of period	124	170	181
Severance [Member]	'	'	'
Restructuring Reserve [Roll Forward]	'	'	'
Liability at beginning of period	36	27	'
Amounts Accrued	9	46	'
Cash Paid	-33	-38	'
Other	-1	1	'
Liability at end of period	11	36	'
Other Restructuring [Member]	'	'	'
Restructuring Reserve [Roll Forward]	'	'	'
Liability at beginning of period	134	154	'
Amounts Accrued	13	32	'
Cash Paid	-32	-50	'
Other	-2	-2	'
Liability at end of period	$113	$134	'

Common_Stock_Details

Common Stock (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended
Share data in Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	31-May-13	Dec. 31, 2013	Dec. 31, 2012
				Common Stock [Member]	Common Stock [Member]	Common Stock [Member]
Equity, Class of Treasury Stock [Line Items]	'	'	'	'	'	'
Common stock repurchased	'	'	'	'	13.2	6.9
Payments for repurchase of common stock	$550,000,000	$230,000,000	$361,000,000	'	'	'
Stock repurchase program, authorized amount	'	'	'	1,000,000,000	'	'
Stock repurchase program, remaining authorized repurchase amount	'	'	'	'	$563,000,000	'

Claims_Lawsuits_And_Other_Cont1

Claims, Lawsuits And Other Contingencies Claims, Lawsuits And Other Contingencies (Details) (GBP £)	Sep. 30, 2013	Dec. 31, 2013
In Millions, unless otherwise specified	Governmental Inquiries and Related Claims [Member]	Other Contingencies-Guarantees [Member]
	lawsuit
Loss Contingencies [Line Items]	'	'
Number of actions instituted by policy holders	2	'
Amount reinsured by third party	'	£ 40

Segment_Information_Details_Fo

Segment Information (Details For MMC's Operating Segments) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]	'		'		'
Revenue	$12,261		$11,924		$11,526
Operating Income (Loss)	2,077		1,829		1,638
Total Assets	16,980		16,288		15,454
Depreciation and Amortization	358		349		332
Capital Expenditures	401		320		280
Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Interest Income, Fiduciary Assets	27		39		47
Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Interest Income, Fiduciary Assets	5		4		4
Operating Segments [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	12,297		11,963		11,566
Operating Income (Loss)	2,266		2,026		1,817
Total Assets	16,543		15,035		13,922
Depreciation and Amortization	307		309		301
Capital Expenditures	313		248		237
Operating Segments [Member] | Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	6,596	[1]	6,350	[1]	6,079	[1]
Operating Income (Loss)	1,421		1,334		1,200
Total Assets	11,365		9,832		9,102
Depreciation and Amortization	192		196		189
Capital Expenditures	158		131		146
Interest Income, Fiduciary Assets	27		39		47
Equity method income	8		11		14
Operating Segments [Member] | Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	5,701	[2]	5,613	[2]	5,487	[2]
Operating Income (Loss)	845		692		617
Total Assets	5,178		5,203		4,820
Depreciation and Amortization	115		113		112
Capital Expenditures	155		117		91
Interest Income, Fiduciary Assets	5		4		4
Intersegment Eliminations [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	-36	[3]	-39	[3]	-40	[3]
Intersegment Eliminations [Member] | Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	5		5		4
Intersegment Eliminations [Member] | Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	31		34		36
Corporate, Non-Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Operating Income (Loss)	-189	[3]	-197	[3]	-179	[3]
Total Assets	437	[4]	1,253	[4]	1,532	[4]
Depreciation and Amortization	51		40		31
Capital Expenditures	$88		$72		$43
[1]	Includes inter-segment revenue of $5 million in both 2013 and 2012 and $4 million in 2011, interest income on fiduciary funds of $27 million, $39 million and $47 million in 2013, 2012 and 2011, respectively, and equity method income of $8 million, $11 million and $14 million in 2013, 2012 and 2011, respectively.
[2]	Includes inter-segment revenue of $31 million, $34 million and $36 million in 2013, 2012 and 2011, respectively, and interest income on fiduciary funds of $5 million in 2013, and $4 million in both 2012 and 2011.
[3]	Includes results of corporate advisory and restructuring business.
[4]	Corporate assets primarily include insurance recoverables, pension related assets, the owned portion of the Company headquarters building and intercompany eliminations.

Segment_Information_Selected_I

Segment Information (Selected Information and Details Of Operating Segment Revenue) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Segment Reporting Information [Line Items]	'		'		'
Revenue	$12,261		$11,924		$11,526
Fixed Assets, Net	828		809		804
United States [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	5,485		5,300		5,131
Fixed Assets, Net	494		494		505
United Kingdom [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	1,979		1,960		1,922
Fixed Assets, Net	121		121		133
Europe [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	1,943		1,879		1,906
Fixed Assets, Net	64		63		65
Asia Pacific [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	1,396		1,346		1,287
Fixed Assets, Net	72		62		37
Other Geographic Areas [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	1,494		1,478		1,320
Fixed Assets, Net	77		69		64
Operating Segments [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	12,297		11,963		11,566
Operating Segments [Member] | Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	6,596	[1]	6,350	[1]	6,079	[1]
Operating Segments [Member] | Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	5,701	[2]	5,613	[2]	5,487	[2]
Intersegment Eliminations [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	-36	[3]	-39	[3]	-40	[3]
Intersegment Eliminations [Member] | Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	5		5		4
Intersegment Eliminations [Member] | Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	31		34		36
Marsh Insurance Group [Member] | Operating Segments [Member] | Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	5,461		5,265		5,031
Guy Carpenter Reinsurance Group [Member] | Operating Segments [Member] | Risk and Insurance Services Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	1,135		1,085		1,048
Mercer Consulting Group [Member] | Operating Segments [Member] | Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	4,241		4,147		4,004
Oliver Wyman Group Consulting Group [Member] | Operating Segments [Member] | Consulting Segment [Member]	'		'		'
Segment Reporting Information [Line Items]	'		'		'
Revenue	$1,460		$1,466		$1,483
[1]	Includes inter-segment revenue of $5 million in both 2013 and 2012 and $4 million in 2011, interest income on fiduciary funds of $27 million, $39 million and $47 million in 2013, 2012 and 2011, respectively, and equity method income of $8 million, $11 million and $14 million in 2013, 2012 and 2011, respectively.
[2]	Includes inter-segment revenue of $31 million, $34 million and $36 million in 2013, 2012 and 2011, respectively, and interest income on fiduciary funds of $5 million in 2013, and $4 million in both 2012 and 2011.
[3]	Includes results of corporate advisory and restructuring business.