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Investments in Associates and Joint Ventures - Summary of Reconciliation of Carrying Amount of Interests in the Associates and Joint Ventures (Parenthetical) (Detail) | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
K Bank Inc. [member] |  |
Disclosure Of Associates And Joint Ventures [Line Items] |  |
Percentage of non-voting convertible stock are excluded | 12.10% | 12.10%

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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
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Proportion of non-voting rights in associate. + References No definition available. + Details
Name: | kt_ProportionOfNonvotingRightsInAssociate
Namespace Prefix: | kt_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |