Initial allocation for purchase of principal amount outstanding on notes

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Namespace Prefix:	mmc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Revised purchase price allocation for principal amount outstanding of notes.

+ Details

Name:	mmc_RevisedPurchasePriceAllocationForPrincipalAmountOutstandingOfNotes
Namespace Prefix:	mmc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Upper limit for tender purchase of aggregate principal amount.

+ Details

Name:	mmc_UpperLimitForTenderPurchaseOfAggregatePrincipalAmount
Namespace Prefix:	mmc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.16)
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.13,16)
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ 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 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

Name:	us-gaap_DebtInstrumentInterestRateEffectivePercentage
Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Interest rate stated in the contractual debt agreement.

+ References

+ Details

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Namespace Prefix:	us-gaap
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year or the normal operating cycle, if longer plus capital lease obligations due to be paid more than one year after 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 22
-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Staff Accounting Bulletin (SAB)
-Number Topic 6
-Section H

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 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

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

Debt (Schedule Of Outstanding Debt) (Details) (USD $) In Millions, unless otherwise specified	Jul. 27, 2011	Jul. 15, 2011	Jul. 12, 2011	Jun. 30, 2011	Jun. 27, 2011	Dec. 31, 2010
Long-term debt, current and noncurrent				$ 3,033		$ 3,034
Current portion of long-term debt		600		260		8
Long-term debt and capital lease obligations				2,773		3,026
Senior Debt Obligations Due 2012 [Member]
Long-term debt and capital lease obligations				252		253
Debt instrument, interest rate, stated percentage				6.25%
Debt instrument, interest rate, effective percentage				5.10%
Senior Debt Obligations Due 2013 [Member]
Long-term debt and capital lease obligations				250		250
Debt instrument, interest rate, stated percentage				4.85%
Senior Debt Obligations Due 2033 [Member]
Long-term debt and capital lease obligations				296		296
Debt instrument, interest rate, stated percentage				5.875%
Senior Debt Obligations Due 2014 [Member]
Long-term debt and capital lease obligations				653	650	648
Debt instrument, interest rate, stated percentage				5.375%	5.375%
Upper limit for tender purchase of aggregate principal amount					500
Revised purchase allocation for principal amount outstanding of notes		330
Senior Debt Obligations Due 2015 [Member]
Long-term debt and capital lease obligations				747	750	747
Debt instrument, interest rate, stated percentage				5.75%	5.75%
Upper limit for tender purchase of aggregate principal amount	500
Initial allocation for purchase of principal amount outstanding on notes			250
Revised purchase allocation for principal amount outstanding of notes		270
Senior Debt Obligations Due 2019 [Member]
Long-term debt and capital lease obligations				398		398
Debt instrument, interest rate, stated percentage				9.25%
Mortgage Due 2035 [Member]
Long-term debt and capital lease obligations				435		439
Debt instrument, interest rate, stated percentage				5.70%
Other [Member]
Long-term debt and capital lease obligations				$ 2		$ 3