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Share Capital - Summary of Share Capital (Parenthetical) (Detail) - shares | Dec. 31, 2020 | Dec. 31, 2019
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Disclosure of classes of share capital [abstract] |  |
Treasury shares | 51,787,959 | 51,787,959

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- 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 Number of treasury shares retired against retained earnings. + References No definition available. + Details
Name: | kt_NumberOfTreasurySharesRetiredAgainstRetainedEarnings
Namespace Prefix: | kt_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant