| Cover Page | Feb. 25, 2021 | Dec. 31, 2020 |
| Document Information [Line Items] | ||
| Document Type | 8-K | |
| Document Period End Date | Apr. 30, 2021 | |
| Entity Registrant Name | GCM Grosvenor Inc. | |
| Entity Incorporation, State or Country Code | DE | |
| Entity File Number | 001-39716 | |
| Entity Tax Identification Number | 85-2226287 | |
| Entity Address, Address Line One | 900 North Michigan Avenue | |
| Entity Address, Address Line Two | Suite 1100 | |
| Entity Address, City or Town | Chicago | |
| Entity Address, State or Province | IL | |
| Entity Address, Postal Zip Code | 60611 | |
| City Area Code | 312 | |
| Local Phone Number | 506-6500 | |
| Written Communications | false | |
| Soliciting Material | false | |
| Pre-commencement Tender Offer | false | |
| Pre-commencement Issuer Tender Offer | false | |
| Entity Emerging Growth Company | true | |
| Entity Ex Transition Period | false | |
| Entity Central Index Key | 0001819796 | |
| Amendment Flag | false | |
| Common Stock [Member] | ||
| Document Information [Line Items] | ||
| Title of 12(b) Security | Class A common stock, par value $0.0001 per share | |
| Trading Symbol | GCMG | |
| Security Exchange Name | NASDAQ | |
| Warrant [Member] | ||
| Document Information [Line Items] | ||
| Title of 12(b) Security | Warrants to purchase one share of Class A common stock | |
| Trading Symbol | GCMGW | |
| Security Exchange Name | NASDAQ |
