Name:	mco_AggregateAmountDueAtMaturity
Namespace Prefix:	mco_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Default provision under the Company's 2010 Senior Notes whereby an event of default will occur if the Company or certain of its subsidiaries fail to pay the principal of any indebtedness (as defined in the Indenture) when due at maturity in an aggregate of $50 million or more, or a default occurs that results in the acceleration of the maturity of the Company's or certain of its subsidiaries' indebtedness in an aggregate amount of $50 million or more.

No definition available.

Name:	mco_MinimumAmountForDefaultOnSeniorNotesPayable
Namespace Prefix:	mco_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Minimum percentage of votes needed by holders of the notes which will result in the notes becoming due and payable pursuant to an event of default.

No definition available.

Name:	mco_MinimumPercentageOfAggregatePrincipalAmountOfAllNotes
Namespace Prefix:	mco_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of principal amount being prepaid, plus accrued and unpaid interest

No definition available.

Name:	mco_PercentageOfPrincipalAmountBeingPrepaidPlusAccruedAndUnpaidInterest
Namespace Prefix:	mco_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of principal amount that the Company would be required to pay upon the occurrence of a "Change in Control Triggering Event as defined in the note agreements".

No definition available.

Name:	mco_PercentageOfPrincipalAmountPlusAccruedAndUnpaidInterestToDateOfPurchase
Namespace Prefix:	mco_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Face (par) amount of debt instrument at time of issuance.

Reference 1: 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 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Contractual interest rate for funds borrowed, under the debt agreement.

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

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Date the credit facility terminates, in CCYY-MM-DD format.

Reference 1: 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

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