Information About Non-controlling Interests - Summary of Changes in Ownership Interest on the Equity Attributable to Owners (Detail) - KRW (₩) ₩ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Disclosure of subsidiaries [abstract]
Carrying amount of non-controlling interests acquired	₩ 1,750	₩ (9,566)	₩ (194)
Consideration paid to non-controlling interests	9,878	484	11,312
Excess of consideration paid recognized in parent's equity	₩ 11,628	₩ (9,082)	₩ 11,118

Excess of Consideration Paid Recognized In Parent's Equity

No definition available.

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Namespace Prefix:	kt_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration