Related Party, Commitment to Investment Vehicle

No definition available.

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Namespace Prefix:	fsk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Related Party, Investment Vehicle

+ References

No definition available.

+ Details

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Namespace Prefix:	fsk_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Percentage of total assets less all liabilities and indebtedness not represented by senior security, to senior security representing indebtedness.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name Investment Company Act of 1940
-Section 61
-Paragraph a
-Subparagraph (1)
-Publisher SEC

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Base rate for management and service fees under arrangement to manage operations, including, but not limited to, investment.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 13
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481990/310-10-45-13

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(i))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(c)(2)(ii))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 946
-SubTopic 220
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.6-07(2)(g)(3))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479134/946-220-S99-1

+ Details

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Balance Type:	na
Period Type:	duration

- Details

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- Details

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Data Type:	na
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- Details

Name:	us-gaap_RelatedPartyTransactionAxis=fsk_AffiliatedPurchaserProgramMember
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Related Party Transactions - Narrative (Details) - USD ($) $ in Millions				3 Months Ended
	Jun. 15, 2019	Jun. 14, 2019	Dec. 20, 2018	Mar. 31, 2025	Mar. 31, 2024
Related Party Transaction [Line Items]
Asset coverage per ratio (as percent)				182.00%	185.00%
Investment Advisory Agreement \| FS/KKR Advisor, LLC
Related Party Transaction [Line Items]
Management and service fees, base rate	1.00%	1.50%	1.50%
Asset coverage per ratio (as percent)	150.00%	200.00%
Affiliated Purchaser Program \| FS/KKR Advisor, LLC
Related Party Transaction [Line Items]
Commitment to investment vehicle				$ 100
Investment vehicle				$ 350