Interest Rate Swap for Hedging

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- Definition

Interest Rate Swap Maturity

+ Details

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Period Type:	duration

- Definition

Interest rate swaps, fair value adjustment.

+ Details

Name:	mmc_InterestRateSwapsFairValueAdjustment
Namespace Prefix:	mmc
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Line of Credit Facility Term

+ Details

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- Definition

Interest rate stated in the contractual debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of the hedged item as of the balance sheet date related to the derivative. For example, the hedged balance on a debt instrument.

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Gross amount of debt extinguished.

+ Details

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Period Type:	duration

- Definition

Assertion that the amount of fair value hedge ineffectiveness is immaterial.

+ Details

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

+ Details

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Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Balance Type:	credit
Period Type:	instant

- Definition

Reflects when the credit facility first became available, which may be presented in a variety of ways (year, month and year, day, month and year, quarter).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19, 22

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19(b),22(b))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

The percentage points (also referred to as 'margin') added to the reference rate as stated in the loan agreement and used to compute the variable rate on the loans receivable. For instance, the loan agreement might state that the interest rate the borrower is obligated to pay is the London Interbank Offered Rate (LIBOR) plus three quarters (3/4) of a percentage point adjusted quarterly (each three months). LIBOR in this example is the index or reference rate, 3/4 percentage point is the margin, the reference rate plus the margin is the fully indexed rate. This element would be used to report separately the margin.

+ Details

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- Definition

Total of the portions of the carrying amounts as of the balance sheet date of long-term debt, which may include notes payable, bonds payable, debentures, mortgage loans, and commercial paper, which are scheduled to be repaid within one year or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 20

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Article 5

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.19,20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Number of interest rate derivative instruments held by the entity at the reporting date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1B

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 10

-Section 50

-Paragraph 1A

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6935481&loc=SL5579245-113959

+ Details

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- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ Details

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Debt (Narrative) (Details) (USD $)	0 Months Ended	1 Months Ended	9 Months Ended				9 Months Ended		0 Months Ended				0 Months Ended			9 Months Ended
Debt (Narrative) (Details) (USD $)	Oct. 13, 2011	Feb. 28, 2011	Sep. 30, 2011	Sep. 30, 2010	Jul. 15, 2011	Dec. 31, 2010	Sep. 30, 2011 September 2011 Debt Obligation [Member]	Oct. 13, 2011 September 2011 Debt Obligation [Member]	Jul. 15, 2011 Senior Debt Obligations Due 2014 [Member]	Sep. 30, 2011 Senior Debt Obligations Due 2014 [Member]	Jun. 27, 2011 Senior Debt Obligations Due 2014 [Member]	Sep. 30, 2010 Senior Debt Obligations Due 2010 [Member]	Jul. 15, 2011 Senior Debt Obligations Due 2015 [Member]	Sep. 30, 2011 Senior Debt Obligations Due 2015 [Member]	Jun. 27, 2011 Senior Debt Obligations Due 2015 [Member]	Sep. 30, 2011 Senior Debt Obligations Due In Ten Years [Member]
Debt instrument, interest rate, stated percentage										5.375%	5.375%	5.15%		5.75%	5.75%	4.80%
Senior notes			$ 260,000,000		$ 600,000,000	$ 8,000,000						$ 550,000,000
Line of Credit Facility Term							5 years
Revised Purchase Price Allocation For Principal Amount Outstanding of Notes									330,000,000				270,000,000
Number of interest rate swaps		2
Floating rate three-month LIBOR plus fixed spread interest percentage		3.726%
Interest rate swaps, fair value adjustment		0
Swap agreements, effectiveness recognized during the period			0
Interest rate swap for hedging		125,000,000
Interest rate swap maturity, in years		3.5
Revolving credit facility, initiation date	October 13, 2011
5.375% senior notes due in 2014, hedged value										250,000,000
Line of credit facility, current borrowing capacity	1,000,000,000							1,000,000,000
Revolving credit facility, amount outstanding			0
Proceeds from issuance of debt			$ 496,000,000													$ 500,000,000