v2.4.0.6
Document and Entity Information (USD $)
12 Months Ended
Dec. 31, 2012
Feb. 22, 2013
Jun. 30, 2012
Entity Information [Line Items]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Dec. 31, 2012    
Document Fiscal Year Focus 2012    
Document Fiscal Period Focus FY    
Trading Symbol MSCI    
Entity Registrant Name MSCI INC.    
Entity Central Index Key 0001408198    
Current Fiscal Year End Date --12-31    
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   120,229,566  
Entity Public Float     $ 4,067,628,516