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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, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure Of Associates And Joint Ventures [Line Items]
Share gain from associates and joint ventures	₩ 18,041	₩ (3,304)	₩ (5,467)
KT Investment Co., Ltd. [member]
Disclosure Of Associates And Joint Ventures [Line Items]
Share gain from associates and joint ventures	₩ 279	₩ 52	₩ 445

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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
-Number 8
-IssueDate 2020-01-01
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name IFRS
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-URIDate 2020-01-01

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Note Effective on first application of IFRS 9
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
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- References

No definition available.

+ Details

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