Investment Portfolio - Narrative (Details) $ in Millions		3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 18, 2021 USD ($)	Jun. 30, 2024 USD ($) company	Jun. 30, 2023 USD ($)	Jun. 30, 2024 USD ($) company	Jun. 30, 2023 USD ($)	Dec. 31, 2023 USD ($) company
Schedule of Investments [Line Items]
Amount funded to joint venture				$ 1,799.8
Net realized gain (loss) on investments:				(307.0)	$ (272.0)
Receivable for investments sold and repaid		$ 225.0		225.0		$ 246.0
Unfunded Debt Securities
Schedule of Investments [Line Items]
Unfunded commitments		1,269.5		1,269.5		995.1
Unfunded Equity/Other commitments
Schedule of Investments [Line Items]
Unfunded commitments		481.4		481.4		616.4
Partnership Interest
Schedule of Investments [Line Items]
Unfunded commitments		735.2		735.2		$ 560.2
FS/KKR Advisor, LLC
Schedule of Investments [Line Items]
Cost basis of investments sold				188.7
Proceeds from sale of investments				190.0
Net realized gain (loss) on investments:				1.3
Receivable for investments sold and repaid		$ 199.8		199.8
Credit Opportunities Partners JV, LLC
Schedule of Investments [Line Items]
Aggregate credit opportunities partners	$ 2,640.0
Credit opportunities partners JV, LLC, entitled to a fee percentage	0.25%
FS KKR Capital Corp.
Schedule of Investments [Line Items]
Contributed capital to committed capital ratio	87.50%
Joint venture voting control, percentage	50.00%
Amount funded to joint venture				$ 1,574.8
SCRS
Schedule of Investments [Line Items]
Contributed capital to committed capital ratio	12.50%
Joint venture voting control, percentage	50.00%
Controlled/affiliated
Schedule of Investments [Line Items]
Number of investments in portfolio companies | company		29		29		27
Net realized gain (loss) on investments:		$ (1.0)	$ (172.0)	$ (9.2)	(172.0)	$ (174.8)
Non-controlled/affiliated
Schedule of Investments [Line Items]
Number of investments in portfolio companies | company		11		11		13
Net realized gain (loss) on investments:		$ 2.0	$ (3.0)	$ (7.8)	$ (3.0)	$ (21.2)