Cover Page - USD ($) shares in Millions, $ in Billions	12 Months Ended
	Dec. 31, 2019	Jan. 31, 2020	Jun. 30, 2019
Entity Information [Line Items]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2019
Document Transition Report	false
Entity File Number	1-14037
Entity Registrant Name	MOODY’S CORPORATION
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	13-3998945
Entity Address, Address Line One	7 World Trade Center at 250 Greenwich Street
Entity Address, City or Town	New York
Entity Address, State or Province	NY
Entity Address, Postal Zip Code	10007
City Area Code	212
Local Phone Number	553-0300
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Public Float			$ 37.0
Entity Common Stock, Shares Outstanding (in shares)		187.4
Documents Incorporated by Reference	Portions of the Registrant’s definitive proxy statement for use in connection with its annual meeting of stockholders scheduled to be held on April 21, 2020, are incorporated by reference into Part III of this Form 10-K.
Entity Central Index Key	0001059556
Document Fiscal Period Focus	FY
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Common Stock, par value $0.01 per share
Entity Information [Line Items]
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	MCO
Security Exchange Name	NYSE
1.75% Senior Notes Due 2027
Entity Information [Line Items]
Title of 12(b) Security	1.75% Senior Notes Due 2027
Trading Symbol	MCO 27
Security Exchange Name	NYSE
0.950% Senior Notes Due 2030
Entity Information [Line Items]
Title of 12(b) Security	0.950% Senior Notes Due 2030
Trading Symbol	MCO 30
Security Exchange Name	NYSE