Name:	mco_ConditionalOfferCashPaymentMaximum
Namespace Prefix:	mco_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The minimum cash payment (assuming exchange rates in effect at the date of the offer), pursuant to a conditional open offer for the Company to acquire additional shares in ICRA Limited

No definition available.

Name:	mco_ConditionalOfferCashPaymentMinimum
Namespace Prefix:	mco_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The maximum shares to be acquired pursuant to a conditional open offer for the Company to purchase additional shares of ICRA Limited

No definition available.

Name:	mco_ConditionalOfferSharesAcquiredMaximum
Namespace Prefix:	mco_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

The minimum shares to be acquired pursuant to a conditional open offer for the Company to purchase additional shares of ICRA Limited

No definition available.

Name:	mco_ConditionalOfferSharesAcquiredMinimum
Namespace Prefix:	mco_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Minimum exercise price on put/call option agreement for the remaining ownership interest in Copal Partners Ltd.

No definition available.

Name:	mco_MinimumExercisePrice
Namespace Prefix:	mco_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

The minimum shares to be acquired pursuant to a conditional open offer for the Company to purchase additional shares of ICRA Limited

No definition available.

Name:	mco_OfferPricePerShare
Namespace Prefix:	mco_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 159

-Paragraph 18

-Subparagraph f

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009.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

-Name Accounting Standards Codification

-Topic 323

-SubTopic 10

-Section 50

-Paragraph 3

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 18

-Paragraph 20

-Subparagraph a (1)

-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.

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

The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

No definition available.