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Investments in Associates and Joint Ventures - Summary of Reconciliation of Carrying Amount of Interests in the Associates and Joint Ventures (Parenthetical) (Detail)	12 Months Ended
	Dec. 31, 2017
K Bank Inc. [member]
Disclosure of associates and joint ventures [line items]
Percentage of non-voting convertible stock are excluded	8.00%

X

- Definition

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

+ References

No definition available.

+ Details

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

X

- Definition

Proportion of non-voting rights in associate

+ References

No definition available.

+ Details

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

X

- Details

Name:	ifrs-full_SignificantInvestmentsInAssociatesAxis=kt_KBankIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: