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Accumulated Other Comprehensive Income and Other Components of Equity - Summary of Other Components of Equity (Parenthetical) (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Miscellaneous equity [abstract] |  |
Number of treasury shares granted | 125,412 |
Treasury shares, Amount directly reflected in equity | ₩ 653 | ₩ 738

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

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- Definition Number of treasury shares granted. + References No definition available. + Details
Name: | kt_NumberOfTreasurySharesGranted
Namespace Prefix: | kt_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition The value of treasury shares directly reflected in equity. + References No definition available. + Details
Name: | kt_TreasurySharesAmountDirectlyReflectedInEquity
Namespace Prefix: | kt_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration