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Trade and Other Receivables - Summary of Other Receivables (Parenthetical) (Detail) - KRW (₩) ₩ in Millions | Dec. 31, 2020 | Dec. 31, 2019
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BC Card Co., Ltd. [member] |  |
Disclosure of financial assets [line items] |  |
Settlement receivable included in other receivables | ₩ 986,384 | ₩ 1,786,610

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- Definition Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table. + References No definition available. + Details
Name: | ifrs-full_DisclosureOfFinancialAssetsLineItems
Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Settlement receivable included in other eceivables. + References No definition available. + Details
Name: | kt_SettlementReceivableIncludedInOtherReceivables
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
Name: | ifrs-full_SignificantInvestmentsInSubsidiariesAxis=kt_BCCardCoLtdMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |