Cover - shares	9 Months Ended
	Sep. 30, 2022	Oct. 31, 2022
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2022
Document Transition Report	false
Entity 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
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
Entity Shell Company	false
Title of 12(b) Security	Common stock, par value $0.001
Trading Symbol	FSK
Security Exchange Name	NYSE
Entity Common Stock, Shares Outstanding		282,978,008
Entity Central Index Key	0001422183
Amendment Flag	false
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31