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Commitments and Contingencies - Additional Information (Detail) ₩ in Millions	12 Months Ended
	Dec. 31, 2020 KRW (₩) Lawsuits	Dec. 31, 2019 KRW (₩)
Commitments and contingencies [abstract]
Severally liable for reimbursement	₩ 1,618
Number of lawsuits | Lawsuits	195
Litigation settlement claim amount	₩ 110,409	₩ 214,877
Litigation provision	₩ 76,500	62,241
New town development consortium percentage of ownership interest	2.50%
Contract amount not yet recognized as liabilities	₩ 596,983	₩ 851,798

X

- Definition

The amount expected to be reimbursed by another party on expenditures to settle other provisions. [Refer: Other provisions]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 37
-IssueDate 2020-01-01
-Paragraph 85
-Subparagraph c
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&anchor=para_85_c&doctype=Standard
-URIDate 2020-01-01

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The amount of provision for legal proceedings. [Refer: Other provisions]

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 37
-IssueDate 2020-01-01
-Section Example 10 A court case
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&doctype=Illustrative%20Examples&dita_xref=IAS37_IE_C_ex10_TI
-URIDate 2020-01-01

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Name IAS
-Number 37
-IssueDate 2020-01-01
-Paragraph 87
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=37&code=ifrs-tx-2020-en-r&anchor=para_87&doctype=Standard
-URIDate 2020-01-01

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Acquisition contract agreement not yet recognized as liabilities.

+ References

No definition available.

+ Details

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Namespace Prefix:	kt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Commitments and contingencies [abstract]

+ References

No definition available.

+ Details

Name:	kt_CommitmentsAndContingenciesAbstract
Namespace Prefix:	kt_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Guarantee interest percentage.

+ References

No definition available.

+ Details

Name:	kt_GuaranteeInterestPercentage
Namespace Prefix:	kt_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Litigation settlements claim amount.

+ References

No definition available.

+ Details

Name:	kt_LitigationSettlementsClaimAmount
Namespace Prefix:	kt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Number of law suits faced.

+ References

No definition available.

+ Details

Name:	kt_NumberOfLawsuitsFaced
Namespace Prefix:	kt_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration