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

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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_
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Balance Type:	na
Period Type:	duration

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- 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

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- Details

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