Related Party Transactions - Narrative (Details) - USD ($) $ in Millions					12 Months Ended			18 Months Ended	42 Months Ended
		Jun. 15, 2019	Jun. 14, 2019	Dec. 20, 2018	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2022	Dec. 31, 2024	Dec. 31, 2021	Dec. 31, 2020
Related Party Transaction [Line Items]
Asset coverage per ratio (as percent)					190.00%	183.00%	180.00%	180.00%	190.00%	184.00%	177.00%
Incentive fees waived	[1]				$ 0	$ 0	$ 60
FS/KKR Advisor, LLC
Related Party Transaction [Line Items]
Incentive fees waived quarterly									$ 15
Investment Advisory Agreement | FS/KKR Advisor, LLC
Related Party Transaction [Line Items]
Management and service fees, base rate (as percent)		1.00%	1.50%	1.50%
Asset coverage per ratio (as percent)		150.00%	200.00%
Incentive fees waived quarterly								$ 15
Incentive fees waived								$ 90
Affiliated Purchaser Program | FS/KKR Advisor, LLC
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.