Document and Entity Information
| Document and Entity Information | Oct. 05, 2020 |
| Cover [Abstract] | |
| Document Type | 8-K/A |
| Amendment Flag | true |
| Amendment Description | This Form 8-K/A is being filed as an amendment (“Amendment No. 1”) to the Current Report on Form 8-K filed by MSCI Inc. (the “Company”) under Item 5.02 on September 25, 2020 reporting that, pursuant to mutual agreement, Ms. Linda S. Huber, was stepping down from her role as Chief Financial Officer (“CFO”) of the Company and Mr. Andrew C. Wiechmann was succeeding her as CFO, effective September 25, 2020. This Amendment No. 1 is being filed to provide the material terms of the agreement the Company entered into with Ms. Huber in connection with her departure, the terms of which were not yet finalized as of the time of filing of the current report on Form 8-K on September 25, 2020. |
| Document Period End Date | Oct. 5, 2020 |
| Entity Registrant Name | MSCI Inc. |
| Entity Central Index Key | 0001408198 |
| Entity Emerging Growth Company | false |
| Entity File Number | 001-33812 |
| 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 St., 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common Stock, par value $0.01 per share |
| Trading Symbol | MSCI |
| Security Exchange Name | NYSE |