Document - Document and Entity Information - $ / shares shares in Millions	6 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Cover [Abstract]
Document Type	10-Q
Entity Registrant Name	MOODYS CORP /DE/
Entity Central Index Key	0001059556
Entity Shell Company	false
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Document Period End Date	Jun. 30, 2019
Document Fiscal Period Focus	Q2
Entity Address, Address Line One	7 World Trade Center
Entity Address, Address Line Two	250 Greenwich Street
Entity Address City Or Town	New York
Entity Address, State Or Province	NY
Entity Address Postal Zip Code	10007
Phone Fax Number Description	Registrant’s telephone number, including area code:
City Area Code	(212)
Local Phone Number	553-0300
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Trading Symbol	MCO
Entity Common Stock Shares Outstanding	189.2
Common Stock Par Or Stated Value Per Share	$ 0.01	$ 0.01
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Security Exchange Name	NYSE
Entity File Number	1-14037
Entity Incorporation State Country Code	DE
Entity Tax Identification Number	13-3998945
Document Quarterly Report	true
Document Transition Report	false
Security 12b Title	Common Stock
Entity Ex Transition Period	false