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Investments in Associates and Joint Ventures - Additional Information (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Disclosure of associates [abstract] |  |
Loss from associates and joint ventures not recognized | ₩ 992 | ₩ 6,124
Accumulated comprehensive loss of associates and joint ventures not recognized | ₩ 8,228 | ₩ 12,599

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

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- Definition The cumulative amount of the unrecognised share of losses of associates and joint ventures if the entity has stopped recognising its share of losses when applying the equity method. + References No definition available. + Details
Name: | kt_CumulativeUnrecognisedShareOfLossesOfAssociatesAndJointVentures
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount of the unrecognised share of associate and joint venture losses if the entity has stopped recognising its share of losses when applying the equity method. + References No definition available. + Details
Name: | kt_UnrecognisedShareOfLossesOfAssociatesAndJointVentures
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration