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Borrowings - Summary of Long-term Borrowings (Parenthetical) (Detail) | 12 Months Ended
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Dec. 31, 2020
Inter-Korean Cooperation Fund [member] |
Disclosure of detailed information about borrowings [line items] |
Long term debt repayment | The above Inter-Korean Cooperation Fund is repayable in installments over 13 years after a seven-year grace period.
Vessel facility loans [member] | Shinhan Bank [member] |
Disclosure of detailed information about borrowings [line items] |
LIBOR rate | 0.238%
Vessel facility loans [member] | Kookmin Bank [member] |
Disclosure of detailed information about borrowings [line items] |
LIBOR rate | 0.238%

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- Definition The adjustment to the basis (reference rate) used for calculation of the interest rate on borrowings. [Refer: Borrowings] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IFRS -Number 7 -IssueDate 2020-01-01 -Paragraph 7 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2020-en-r&anchor=para_7&doctype=Standard -URIDate 2020-01-01 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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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 Long term debt repayment description. + References No definition available. + Details
Name: | kt_LongTermDebtRepaymentDescription
Namespace Prefix: | kt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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

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

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

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