| Document and Entity Information | 12 Months Ended |
| Dec. 31, 2020shares | |
| Document Information [Line Items] | |
| Document Type | 20-F/A |
| Amendment Flag | true |
| Document Period End Date | Dec. 31, 2020 |
| Document Fiscal Year Focus | 2020 |
| Document Fiscal Period Focus | FY |
| Document Registration Statement | false |
| Document Annual Report | true |
| Document Transition Report | false |
| Document Shell Company Report | false |
| Trading Symbol | CSAN |
| Entity Registrant Name | COSAN S.A. |
| Entity Central Index Key | 0001430162 |
| Current Fiscal Year End Date | --12-31 |
| Entity File Number | 001-40015 |
| Entity Filer Category | Non-accelerated Filer |
| Entity Voluntary Filers | No |
| Entity Current Reporting Status | Yes |
| Entity Well-known Seasoned Issuer | No |
| Entity Common Stock, Shares Outstanding | 382,460,962 |
| Entity Emerging Growth Company | false |
| Entity Interactive Data Current | Yes |
| Entity Shell Company | false |
| Title of 12(b) Security | Common shares, no par value* |
| Security Exchange Name | NYSE |
| Entity Address, Country | BR |
| Document Accounting Standard | International Financial Reporting Standards |
| ICFR Auditor Attestation Flag | true |
| Amendment Description | We are amending our Annual Report on Form 20-F for the fiscal year ended December 31, 2020 as originally filed with the U.S. Securities and Exchange Commission (the “SEC”) on April 30, 2021 (the “Original Annual Report”) and as amended by Amendment No. 1 to the Original Annual Report filed with the SEC on September 3, 2021 (“Amendment No. 1” and together with the Original Annual Report, the “Annual Report”) to replace the report of the independent registered public accounting firm included in the financial statements of Raízen Group – comprised of Raízen Energia S.A. and Raízen Combustíveis S.A. for the fiscal years ended March 31, 2021, 2020 and 2019 previously filed as Exhibit 13.3 with the separate independent registered public accounting firms’ reports for the corresponding fiscal years. |
| Entity Incorporation, State or Country Code | D5 |
| Entity Address, Address Line One | Av. Brigadeiro Faria Lima, 4,100 – 16th floor |
| Entity Address, Postal Zip Code | SP |
| Entity Address, City or Town | São Paulo |
| Business Contact [Member] | |
| Document Information [Line Items] | |
| Entity Address, Country | BR |
| Entity Address, Address Line One | Av. Brigadeiro Faria Lima, 4,100 – 16th floor |
| Entity Address, Postal Zip Code | SP |
| Entity Address, City or Town | São Paulo |
| Contact Personnel Name | Marcelo Eduardo Martins |
| City Area Code | +55 11 |
| Local Phone Number | 3897-9797 |
