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Deposits (Details) - USD ($) | Jun. 30, 2021 | Jun. 30, 2020
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Statistical Disclosure for Banks [Abstract] |  |
Deposits | $ 250,000 | $ 250,000
Balances of deposit accounts | $ 11,200,000 | $ 13,000,000.0

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- Definition BankDeposits + References No definition available. + Details
Name: | kffb_BankDeposits
Namespace Prefix: | kffb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition TimeDeposits250000OrMore + References No definition available. + Details
Name: | kffb_TimeDeposits250000OrMore
Namespace Prefix: | kffb_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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