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    <dei:EntityRegistrantName contextRef="P11_20_2024To11_20_2024" id="ixv-421">FS KKR Capital Corp.</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode contextRef="P11_20_2024To11_20_2024" id="ixv-422">MD</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber contextRef="P11_20_2024To11_20_2024" id="ixv-423">814-00757</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber contextRef="P11_20_2024To11_20_2024" id="ixv-424">26-1630040</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1 contextRef="P11_20_2024To11_20_2024" id="ixv-425">201 Rouse Boulevard</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown contextRef="P11_20_2024To11_20_2024" id="ixv-426">Philadelphia</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince contextRef="P11_20_2024To11_20_2024" id="ixv-427">PA</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode contextRef="P11_20_2024To11_20_2024" id="ixv-428">19112</dei:EntityAddressPostalZipCode>
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    <dei:Security12bTitle contextRef="P11_20_2024To11_20_2024" id="ixv-435">Common stock</dei:Security12bTitle>
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    <cef:LongTermDebtTableTextBlock contextRef="P11_20_2024To11_20_2024" id="ixv-214">On November&#160;20, 2024, FS KKR Capital Corp. (the &#x201c;Company&#x201d;) and U.S. Bank Trust Company, National Association (as &lt;div style="white-space: nowrap; letter-spacing: 0px; top: 0px;display:inline;"&gt;&lt;div style="white-space: nowrap; letter-spacing: 0px; top: 0px;display:inline;"&gt;successor-in-interest&lt;/div&gt;&lt;/div&gt; to U.S. Bank National Association) (the &#x201c;Trustee&#x201d;), entered into a Fourteenth Supplemental Indenture (the &#x201c;Fourteenth Supplemental Indenture&#x201d;) to the Indenture, dated July&#160;14, 2014, between the Company and the Trustee (the &#x201c;Base Indenture&#x201d;; and together with the Fourteenth Supplemental Indenture, the &#x201c;Indenture&#x201d;). The Fourteenth Supplemental Indenture relates to the Company&#x2019;s issuance of $600,000,000 aggregate principal amount of its 6.125% notes due 2030 (the &#x201c;Notes&#x201d;).</cef:LongTermDebtTableTextBlock>
    <cef:LongTermDebtPrincipal
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    <cef:LongTermDebtStructuringTextBlock contextRef="P11_20_2024To11_20_2024" id="ixv-218">The Notes will mature on January&#160;15, 2030 and may be redeemed in whole or in part at the Company&#x2019;s option at any time or from time to time at the redemption prices set forth in the Indenture. The Notes bear interest at a rate of 6.125%&#160;per year payable semi-annually in arrears on January&#160;15 and July&#160;15 of each year, beginning on July&#160;15, 2025. The Notes are general unsecured obligations of the Company that rank senior in right of payment to all of the Company&#x2019;s existing and future indebtedness that is expressly subordinated in right of payment to the Notes, rank &lt;div style="font-style: normal; letter-spacing: 0px; top: 0px;display:inline;"&gt;&lt;div style="font-style:italic;display:inline;"&gt;pari passu&lt;/div&gt;&lt;/div&gt; with all existing and future unsecured unsubordinated indebtedness issued by the Company, rank effectively junior to any of the Company&#x2019;s secured indebtedness (including unsecured indebtedness that the Company later secures) to the extent of the value of the assets securing such indebtedness, and rank structurally junior to all existing and future indebtedness (including trade payables) incurred by the Company&#x2019;s subsidiaries, financing vehicles or similar facilities.</cef:LongTermDebtStructuringTextBlock>
    <cef:LongTermDebtDividendsAndCovenantsTextBlock contextRef="P11_20_2024To11_20_2024" id="ixv-440">The Indenture contains certain covenants, including covenants requiring the Company to comply with the asset coverage requirements of Section&#160;18(a)(1)(A) as modified by Section&#160;61(a)(1) and (2)&#160;of the Investment Company Act of 1940, as amended, whether or not it is subject to those requirements, and to provide financial information to the holders of the Notes and the Trustee if the Company is no longer subject to the reporting requirements under the Securities Exchange Act of 1934, as amended. These covenants are subject to important limitations and exceptions that are described in the Indenture.</cef:LongTermDebtDividendsAndCovenantsTextBlock>
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