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Investments in Associates and Joint Ventures - Summary of Changes in Investments in Associates and Joint Ventures (Parenthetical) (Detail) - KRW (₩) ₩ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Disclosure of information about unconsolidated structured entities controlled by investment entity [line items]
Share gain from associates and joint ventures	₩ (5,467)	₩ (13,892)	₩ 2,599
KT Investment Co., Ltd. [member]
Disclosure of information about unconsolidated structured entities controlled by investment entity [line items]
Share gain from associates and joint ventures	₩ 445	₩ 1,588

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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.

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- Definition

The entity's share of the profit (loss) of associates and joint ventures accounted for using the equity method. [Refer: Associates [member]; Investments accounted for using equity method; Joint ventures [member]; Profit (loss)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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-IssueDate 2018-01-01
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-Subparagraph g
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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-IssueDate 2018-01-01
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-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=4&date=2018-03-02&anchor=para_39M_b&doctype=Standard&book=b
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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-URIDate 2018-03-16

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