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

Short -Term Investments - Additional Information (Detail)	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014 Minimum [Member]	Dec. 31, 2013 Minimum [Member]	Jun. 30, 2014 Maximum [Member]	Dec. 31, 2013 Maximum [Member]
Schedule Of Investments [Line Items]
Short-term investment securities, maturity date	90	90
Short Term Investments Maturity Period			1	1	12	9