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Trade and Other Payables - Summary of Other Payables (Parenthetical) (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Trade and other payables [abstract] |  |
Settlement payables related to credit card transaction | ₩ 1,007,171 | ₩ 1,824,068

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

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- Definition Credit Card Transaction Settlement Payable + References No definition available. + Details
Name: | kt_CreditCardTransactionSettlementPayable
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration