Interests in Unconsolidated Structured Entities - Schedule of Unconsolidated Structured Entities and Nature of Risks (Details) - KRW (₩) ₩ in Millions	12 Months Ended
Dec. 31, 2025	Dec. 31, 2024
Real Estate Finance
Disclosure of unconsolidated structured entities [line items]
Maximum loss exposure Investment assets	₩ 416,390	₩ 373,638
Investment agreement and others	47,001	84,481
Total	463,391	458,119
PEF and Investment Funds
Disclosure of unconsolidated structured entities [line items]
Maximum loss exposure Investment assets	454,916	547,153
Investment agreement and others	80,871	101,178
Total	535,787	648,331
Unconsolidated structured entities
Disclosure of unconsolidated structured entities [line items]
Maximum loss exposure Investment assets	871,306	920,791
Investment agreement and others	127,872	185,659
Total	₩ 999,178	₩ 1,106,450

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with members defined in one or many axes of the table.

No definition available.

+ Details

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

- Definition

The maximum exposure to the credit risk of financial assets designated as measured at fair value through profit or loss. [Refer: Credit risk [member]; Maximum exposure to credit risk]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 7
-IssueDate 2025-01-01
-Paragraph 9
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=7&code=ifrs-tx-2025-en-r&anchor=para_9_a&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_MaximumExposureToCreditRiskOfFinancialAssets
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount that best represents the entity's maximum exposure to loss from its interests in structured entities. [Refer: Total for all unconsolidated structured entities [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2025-01-01
-Paragraph 29
-Subparagraph c
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2025-en-r&anchor=para_29_c&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_MaximumExposureToLossFromInterestsInStructuredEntities
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of financial or other support (for example, purchasing assets of, or instruments issued by, the structured entity) provided to a structured entity without having a contractual obligation to do so, including assistance in obtaining financial support. [Refer: Total for all subsidiaries [member]; Total for all unconsolidated structured entities [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2025-01-01
-Paragraph 15
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2025-en-r&anchor=para_15_a&doctype=Standard
-URIDate 2025-03-27

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 12
-IssueDate 2025-01-01
-Paragraph 30
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=12&code=ifrs-tx-2025-en-r&anchor=para_30_a&doctype=Standard
-URIDate 2025-03-27

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 79
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_79_a&doctype=Standard
-URIDate 2025-03-27

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 92
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_92_a&doctype=Standard
-URIDate 2025-03-27

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 79
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_79_a&doctype=Standard
-URIDate 2025-03-27

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective 2027-01-01
-Name IFRS
-Number 19
-IssueDate 2025-01-01
-Paragraph 92
-Subparagraph a
-URI https://taxonomy.ifrs.org/xifrs-link?type=IFRS&num=19&code=ifrs-tx-2025-en-r&anchor=para_92_a&doctype=Standard
-URIDate 2025-03-27

+ Details

Name:	ifrs-full_SupportProvidedToStructuredEntityWithoutHavingContractualObligationToDoSo
Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	ifrs-full_UnconsolidatedStructuredEntitiesAxis=kt_RealEstateFinanceMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_UnconsolidatedStructuredEntitiesAxis=ifrs-full_InvestmentFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ifrs-full_UnconsolidatedStructuredEntitiesAxis=ifrs-full_UnconsolidatedStructuredEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: