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Exposures to certain potential tax liabilities assumed in connection with the 2000 Distribution Agreement with Old D&B, as further discussed in the footnotes to the financial statements.

No definition available.

Name:	mco_LegacyTaxLiabilities
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Number of plaintiffs for whom the courts dismissed, in whole or in part, the fraud claims against the Company but allowed the fraud claims to proceed with respect to certain claims of one of those plaintiffs and the claims of the remaining 11 plaintiffs.

No definition available.

Name:	mco_NumberOfPlaintiffsDismissedByCourt
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Data Type:	xbrli:positiveIntegerItemType
Balance Type:	na
Period Type:	duration

Number Of Plaintiffs Filed Motions For Reconsideration

No definition available.

Name:	mco_NumberOfPlaintiffsFiledMotionsForReconsideration
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Data Type:	xbrli:integerItemType
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Number Of Plaintiffs Granted Summary Judgement Motions

No definition available.

Name:	mco_NumberOfPlaintiffsGrantedSummaryJudgementMotions
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Data Type:	xbrli:integerItemType
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The number of Plaintiffs with claims that had been ordered to trial.

No definition available.

Name:	mco_NumberOfPlaintiffsOrderedToTrial
Namespace Prefix:	mco_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_LossContingenciesLineItems
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The portion of the carrying amount as of the balance sheet date of the combined total of loss contingency liabilities which is expected to be resolved after one year or beyond the normal operating cycle, if longer.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 450

-SubTopic 20

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6952336&loc=d3e14326-108349

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 5

-Paragraph 9, 10, 11, 12

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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.

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Number of plaintiffs that have filed claims pertaining to a loss contingency.

No definition available.