| Document and Entity Information Document | Oct. 08, 2021 |
| Entity Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Mar. 10, 2022 |
| Entity Registrant Name | Sema4 Holdings Corp. |
| Entity Central Index Key | 0001818331 |
| Amendment Flag | false |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 001-39482 |
| Entity Tax Identification Number | 85-1966622 |
| Entity Address, Address Line One | 333 Ludlow Street, North Tower, 8th Floor |
| Entity Address, City or Town | Stamford, |
| Entity Address, State or Province | CT |
| Entity Address, Postal Zip Code | 06902 |
| City Area Code | 800 |
| Local Phone Number | 298-6470 |
| 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 |
| Common Stock | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Class A common stock, par value $0.0001 per share |
| Trading Symbol | SMFR |
| Security Exchange Name | NASDAQ |
| Warrant | |
| Entity Information [Line Items] | |
| Title of 12(b) Security | Warrants to purchase one share of Class A common stock, each at an exercise price of $11.50 per share |
| Trading Symbol | SMFRW |
| Security Exchange Name | NASDAQ |
