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Significant Accounting Policies - Additional Information (Detail) - KRW (₩) ₩ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Disclosure of significant accounting policies [line items]
Lease term		Lease term is over 12 months
Description of assets which are not low value		Underlying assets are not low value assets
Bottom of range [member]
Disclosure of significant accounting policies [line items]
Useful lives of investment property, excluding land depreciated cost model	10 years
Top of range [member]
Disclosure of significant accounting policies [line items]
Useful lives of investment property, excluding land depreciated cost model	40 years
IFRS 16 leases [member]
Disclosure of significant accounting policies [line items]
Lease assets and liabilities		₩ 616,759

X

- Definition

The statement that the lessee accounts for leases of low-value assets using the recognition exemption in paragraph 6 of IFRS 16.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 16
-IssueDate 2019-01-01
-Paragraph 60
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2019-en-r&anchor=para_60&doctype=Standard
-URIDate 2019-03-27

+ Details

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

X

- Definition

The statement that the lessee accounts for short-term leases using the recognition exemption in paragraph 6 of IFRS 16. Short-term lease is a lease that, at the commencement date, has a lease term of 12 months or less. A lease that contains a purchase option is not a short-term lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
-Number 16
-IssueDate 2019-01-01
-Paragraph 60
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=16&code=ifrs-tx-2019-en-r&anchor=para_60&doctype=Standard
-URIDate 2019-03-27

+ Details

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

X

- Definition

The useful life, measured as period of time, used for investment property. [Refer: Investment property]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 40
-IssueDate 2019-01-01
-Paragraph 79
-Subparagraph b
-URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=40&code=ifrs-tx-2019-en-r&anchor=para_79_b&doctype=Standard
-URIDate 2019-03-27

+ Details

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Namespace Prefix:	ifrs-full_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Disclosure of significant accounting policies [line items]

+ References

No definition available.

+ Details

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

X

- Definition

Lease assets and liabilities recognized in consolidated financial position.

+ References

No definition available.

+ Details

Name:	kt_LeaseAssetsAndLiabilitiesRecognizedInConsolidatedFinancialPosition
Namespace Prefix:	kt_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

X

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_BottomOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_RangeAxis=ifrs-full_TopOfRangeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	ifrs-full_EffectOfOverlayApproachReclassificationAxis=kt_IFRS16LeasesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: