Cover - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2022	Jan. 31, 2023	Jun. 30, 2022
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2022
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Securities Act File Number	814-00757
Entity Registrant Name	FS KKR Capital Corp.
Entity Incorporation, State or Country Code	MD
Entity Tax Identification Number	26-1630040
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(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	FSK
Security Exchange Name	NYSE
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	true
Entity Shell Company	false
Entity Public Float			$ 5.5
Entity Common Stock, Shares Outstanding		281,174,936
Documents Incorporated by Reference	Portions of the registrant’s definitive Proxy Statement relating to the registrant’s 2023 Annual Meeting of Stockholders, to be filed with the U.S. Securities and Exchange Commission within 120 days following the end of the registrant’s fiscal year ended December 31, 2022, are incorporated by reference in Part III of this annual report on Form 10-K as indicated herein.
Document Fiscal Period Focus	FY
Amendment Flag	false
Document Fiscal Year Focus	2022
Entity Central Index Key	0001422183