Related Party Transactions - Narrative (Details) - USD ($) $ in Millions					12 Months Ended			18 Months Ended
		Jun. 15, 2019	Jun. 14, 2019	Dec. 20, 2018	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2019	Dec. 31, 2018
Related Party Transaction [Line Items]
Asset coverage per ratio					180.00%	184.00%	177.00%	180.00%	192.00%	223.00%
Incentive fees waived	[1]				$ 60	$ 30	$ 0
FS/KKR Advisor, LLC
Related Party Transaction [Line Items]
Incentive fees waived quarterly								$ 15
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 (in percent)		17.50%	20.00%		20.00%
Incentive fees waived quarterly								15
Incentive fees waived								90
FS/KKR Advisor, LLC | Affiliated Purchaser Program
Related Party Transaction [Line Items]
Commitment to investment vehicle						$ 100
Investment vehicle					$ 350			$ 350

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