| Cover Page - USD ($) | 12 Months Ended | | |
| Dec. 31, 2023 | Mar. 31, 2024 | Jun. 30, 2023 |
| Document Information [Line Items] | | | |
| Document Type | 10-K/A | | |
| Document Annual Report | true | | |
| Document Transition Report | false | | |
| Document Period End Date | Dec. 31, 2023 | | |
| Current Fiscal Year End Date | --12-31 | | |
| Entity File Number | 814-00841 | | |
| Entity Registrant Name | FS Specialty Lending Fund | | |
| Entity Incorporation, State or Country Code | DE | | |
| Entity Tax Identification Number | 27-6822130 | | |
| Entity Address, Address Line One | 201 Rouse Boulevard | | |
| Entity Address, City or Town | Philadelphia | | |
| Entity Address, State or Province | PA | | |
| Entity Address, Postal Zip Code | 19112 | | |
| City Area Code | 215 | | |
| Local Phone Number | 495-1150 | | |
| Title of 12(g) Security | Common Stock, par value $0.001 per share | | |
| Entity Well-known Seasoned Issuer | No | | |
| Entity Voluntary Filers | No | | |
| Entity Interactive Data Current | Yes | | |
| Entity Current Reporting Status | Yes | | |
| Entity Filer Category | Non-accelerated Filer | | |
| Entity Small Business | false | | |
| Entity Emerging Growth Company | false | | |
| ICFR Auditor Attestation Flag | false | | |
| Document Financial Statement Error Correction [Flag] | false | | |
| Entity Shell Company | false | | |
| Entity Public Float | | | $ 0 |
| Entity Common Stock, Shares Outstanding | | 455,506,154.632 | |
| Documents Incorporated by Reference [Text Block] | None. | | |
| Amendment Flag | true | | |
| Amendment Description | FS Specialty Lending Fund (the “Company”), which may also be referred to as “we,” “us” or “our,” is filing this Amendment No. 1 (the “Amendment”) to its Annual Report on Form 10-K for the Company’s fiscal year ended December 31, 2023, as originally filed with the Securities and Exchange Commission (the “SEC”) on March 15, 2024 (the “Original Report”). The purpose of this Amendment is to include Part III information, which was to be incorporated by reference by this Amendment in reliance on General Instruction G(3) to Form 10-K. This Amendment also updates, amends and supplements Part IV, Item 15 of the Form 10-K to include the filing of new Exhibits 31.1 and 31.2, certifications of our Chief Executive Officer and Chief Financial Officer, pursuant to Rule 13a-14(a) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”). In addition, the cover page has been updated and amended. The Amendment does not affect any other items in the Original Report, including the Company’s financial statements and the notes to the financial statements. Except as otherwise indicated, the Amendment speaks as of the date of the Original Report and reflects only the changes discussed above. Accordingly, this Amendment should be read in conjunction with the Original Report. | | |
| Entity Central Index Key | 0001501729 | | |
| Document Fiscal Year Focus | 2023 | | |
| Document Fiscal Period Focus | FY | | |
| Auditor Name | Ernst & Young LLP | | |
| Auditor Location | Philadelphia, Pennsylvania | | |
| Auditor Firm ID | 42 | | |
