Investment Portfolio - Narrative (Details)	3 Months Ended			9 Months Ended			12 Months Ended
	Sep. 30, 2022 USD ($) portfolio		Sep. 30, 2021 USD ($)	Sep. 30, 2022 USD ($) portfolio		Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($) portfolio	Jun. 28, 2022 USD ($)	Dec. 31, 2020 USD ($)
Schedule of Investments [Line Items]
Increase in commitment								$ 440,000,000
Amount funded to joint venture				$ 1,799,800,000
Net realized gain (loss) on investments:				214,000,000		$ 123,000,000
Receivable for investments sold and repaid	$ 425,000,000			425,000,000			$ 567,000,000
Fair value	15,791,800,000	[1]		15,791,800,000	[1]		$ 16,101,000,000
FS/KKR Advisor, LLC
Schedule of Investments [Line Items]
Cost basis of investments sold				943,500,000
Proceeds from sale of investments				941,200,000
Net realized gain (loss) on investments:				(2,300,000)
Receivable for investments sold and repaid	$ 398,200,000			$ 398,200,000
Controlled/affiliated investments
Schedule of Investments [Line Items]
Number of investments in portfolio companies	17			17			17
Net realized gain (loss) on investments:	$ (4,000,000)		$ (2,000,000)	$ (42,500,000)		(58,000,000)	$ (48,500,000)
Fair value	$ 2,801,300,000			$ 2,801,300,000			$ 2,684,100,000		$ 1,259,700,000
Non-controlled/affiliated investments
Schedule of Investments [Line Items]
Number of investments in portfolio companies	10			10			16
Net realized gain (loss) on investments:	$ 51,000,000		$ 139,000,000	$ 89,800,000		$ 203,000,000	$ 191,900,000
Fair value	439,200,000			439,200,000			859,000,000.0		$ 533,800,000
Credit Opportunities Partners JV, LLC
Schedule of Investments [Line Items]
Aggregate credit opportunities partners				$ 2,440,000,000
Credit opportunities partners JV, LLC, entitled to a fee percentage				0.25%
Fair value	$ 3,624,500,000			$ 3,624,500,000			$ 3,260,000,000
Number of investments owned in non-accrual status | portfolio	1			1			0
The Company
Schedule of Investments [Line Items]
Contributed capital to committed capital ratio				87.50%
Joint venture voting control, percentage				50.00%
Increase in commitment								$ 385,000,000
Amount funded to joint venture				$ 1,574,800,000
SCRS
Schedule of Investments [Line Items]
Contributed capital to committed capital ratio				12.50%
Joint venture voting control, percentage				50.00%
Debt Securities
Schedule of Investments [Line Items]
Unfunded equity/other commitments	$ 1,042,400,000			$ 1,042,400,000			$ 1,724,100,000
Unfunded Asset Based Finance/Other commitments
Schedule of Investments [Line Items]
Unfunded equity/other commitments	362,800,000			362,800,000			576,900,000
Credit Opportunities Partners JV, LLC | Partnership Interest
Schedule of Investments [Line Items]
Unfunded equity/other commitments	$ 560,200,000			$ 560,200,000			$ 350,200,000

[1] Security may be an obligation of one or more entities affiliated with the named company