<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xml:lang="en-US"
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:cffn="http://www.capfed.com/20260408"
  xmlns:dei="http://xbrl.sec.gov/dei/2025"
  xmlns:ffd="http://xbrl.sec.gov/ffd/2025"
  xmlns:iso4217="http://www.xbrl.org/2003/iso4217"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xbrldi="http://xbrl.org/2006/xbrldi"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef
      xlink:href="https://xbrl.sec.gov/ffd/2025/ffd-2025.xsd"
      xlink:type="simple"/>
    <context id="c-1">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001490906</identifier>
        </entity>
        <period>
            <startDate>2026-04-08</startDate>
            <endDate>2026-04-08</endDate>
        </period>
    </context>
    <context id="c-2">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001490906</identifier>
            <segment>
                <xbrldi:typedMember dimension="ffd:OfferingAxis">
                    <dei:lineNo>1</dei:lineNo>
                </xbrldi:typedMember>
            </segment>
        </entity>
        <period>
            <startDate>2026-04-08</startDate>
            <endDate>2026-04-08</endDate>
        </period>
    </context>
    <unit id="shares">
        <measure>cffn:shares</measure>
    </unit>
    <unit id="usd">
        <measure>iso4217:USD</measure>
    </unit>
    <unit id="number">
        <measure>pure</measure>
    </unit>
    <dei:EntityCentralIndexKey contextRef="c-1" id="f-18">0001490906</dei:EntityCentralIndexKey>
    <ffd:FeeExhibitTp contextRef="c-1" id="f-19">EX-FILING FEES</ffd:FeeExhibitTp>
    <ffd:OffsetTableNa contextRef="c-1" id="f-20">N/A</ffd:OffsetTableNa>
    <ffd:FormTp contextRef="c-1" id="f-1">S-8</ffd:FormTp>
    <ffd:SubmissnTp contextRef="c-1" id="f-2">S-8</ffd:SubmissnTp>
    <dei:EntityRegistrantName contextRef="c-1" id="f-3">Capitol Federal Financial, Inc.</dei:EntityRegistrantName>
    <ffd:PrevslyPdFlg contextRef="c-2" id="f-4">false</ffd:PrevslyPdFlg>
    <ffd:OfferingSctyTp contextRef="c-2" id="f-5">Equity</ffd:OfferingSctyTp>
    <ffd:OfferingSctyTitl contextRef="c-2" id="f-6">Common Stock, $0.01 par value per share</ffd:OfferingSctyTitl>
    <ffd:FeesOthrRuleFlg contextRef="c-2" id="f-7">true</ffd:FeesOthrRuleFlg>
    <ffd:AmtSctiesRegd contextRef="c-2" decimals="0" id="f-8" unitRef="shares">1500000</ffd:AmtSctiesRegd>
    <ffd:MaxOfferingPricPerScty contextRef="c-2" decimals="2" id="f-9" unitRef="usd">7.30</ffd:MaxOfferingPricPerScty>
    <ffd:MaxAggtOfferingPric contextRef="c-2" decimals="0" id="f-10" unitRef="usd">10950000</ffd:MaxAggtOfferingPric>
    <ffd:FeeRate contextRef="c-2" decimals="8" id="f-11" unitRef="number">0.00013810</ffd:FeeRate>
    <ffd:FeeAmt contextRef="c-2" decimals="2" id="f-12" unitRef="usd">1512.2</ffd:FeeAmt>
    <ffd:TtlOfferingAmt contextRef="c-1" decimals="0" id="f-13" unitRef="usd">10950000</ffd:TtlOfferingAmt>
    <ffd:TtlFeeAmt contextRef="c-1" decimals="2" id="f-14" unitRef="usd">1512.2</ffd:TtlFeeAmt>
    <ffd:TtlOffsetAmt contextRef="c-1" decimals="2" id="f-15" unitRef="usd">0</ffd:TtlOffsetAmt>
    <ffd:NetFeeAmt contextRef="c-1" decimals="2" id="f-16" unitRef="usd">1512.2</ffd:NetFeeAmt>
    <ffd:OfferingNote contextRef="c-2" id="f-17">&lt;div style="margin-bottom:5pt;margin-top:5pt;padding-left:28.8pt;text-align:justify;text-indent:-20.88pt"&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:10pt;font-weight:400;line-height:120%"&gt;(1)   Pursuant to Rules 457(c) and 457(h) under the Securities Act of 1933, as amended (the &#x201c;Securities Act&#x201d;), the proposed maximum offering price per share and the maximum aggregate offering price are estimated solely for the purpose of calculating the registration fee and are based on the average of the high and low prices per share of the common stock, par value $0.01 per share (the &#x201c;Common Stock&#x201d;), of Capitol Federal Financial, Inc. as reported on the NASDAQ Stock Market on April 6, 2026.&lt;/span&gt;&lt;/div&gt;&lt;div style="padding-left:28.8pt;text-indent:-20.88pt"&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:10pt;font-weight:400;line-height:120%"&gt;(2)   Pursuant to Rule 416(a) under the Securities Act, this Registration Statement shall also cover any additional shares of Common Stock as may be issuable as a result of a stock split, stock dividend or similar transaction with respect to the Common Stock.&lt;/span&gt;&lt;/div&gt;&lt;div style="padding-left:28.8pt;text-align:justify;text-indent:-20.88pt"&gt;&lt;span style="color:#000000;font-family:'Times New Roman',serif;font-size:10pt;font-weight:400;line-height:120%"&gt;(3)   Represents shares of Common Stock reserved for issuance pursuant to the Capitol Federal Financial, Inc. 2026 Omnibus Incentive Plan.&lt;/span&gt;&lt;/div&gt;</ffd:OfferingNote>
</xbrl>
