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Investment Securities (Details) - USD ($) $ in Millions | Dec. 31, 2021 | Jun. 30, 2021
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Investments, Debt and Equity Securities [Abstract] |  |
Pledged securities | $ 1.7 | $ 1.8

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- Definition The amount of pledged securities. + References No definition available. + Details
Name: | kffb_PledgedSecurities
Namespace Prefix: | kffb_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_InvestmentsDebtAndEquitySecuritiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration