Related Party Transactions - Narrative (Details) $ in Millions					3 Months Ended		6 Months Ended		18 Months Ended
		Jun. 15, 2019	Jun. 14, 2019	Dec. 20, 2018	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) qtr	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) qtr
Related Party Transaction [Line Items]
Asset coverage per ratio					184.00%		184.00%		180.00%
Incentive fees waived	[1]				$ 0	$ 15	$ 0	$ 30
Affiliated Purchaser Program
Related Party Transaction [Line Items]
Commitment to investment vehicle								$ 100
Investment vehicle					$ 350		$ 350
FS/KKR Advisor, LLC | Investment Advisory Agreement
Related Party Transaction [Line Items]
Management and service fees, base rate		1.00%	1.50%	1.50%
Asset coverage per ratio		150.00%	200.00%
Incentive fee percentage		17.50%	20.00%				20.00%
Investment company, preceding calendar quarterly | qtr							11		6
Incentive fees waived quarterly									$ 15
Incentive fees waived									$ 90

[1] See Note 2 and 4 for a discussion of the methodology employed by the Company in calculating the subordinated income incentive fees.