v3.26.1
Cover Page - shares
shares in Millions
 6 Months Ended
Jun. 30, 2026
Jul. 14, 2026
Cover [Abstract]    
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2026  
Document Transition Report false  
Entity File Number 001-33812  
Entity Registrant Name MSCI INC.  
Entity Incorporation, State or Country Code DE  
Entity Tax Identification Number 13-4038723  
Entity Address, Address Line One 7 World Trade Center  
Entity Address, Address Line Two 250 Greenwich Street, 49th Floor  
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 804-3900  
Title of 12(b) Security Common stock, par value $0.01 per share  
Trading Symbol MSCI  
Security Exchange Name NYSE  
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 Common Stock, Shares Outstanding   72.7
Entity Central Index Key 0001408198  
Document Fiscal Year Focus 2026  
Document Fiscal Period Focus Q2  
Current Fiscal Year End Date --12-31  
Amendment Flag false