Short -Term Investments - Additional Information (Detail)	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012
Schedule Of Investments [Line Items]
Short-term investment securities, maturity date	90	90
Minimum
Schedule Of Investments [Line Items]
Short Term Investments Maturity Period	1	1
Maximum
Schedule Of Investments [Line Items]
Short Term Investments Maturity Period	9	11

Minimum number of days until maturity at the time of purchase for an investment to be deemed at short-term investment under the Company's accounting policy

No definition available.

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