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Intangible Assets - Additional Information (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Disclosure of detailed information about intangible assets [line items] |  |
Acquisition cost | ₩ 201,461 |
Remaining useful life of Frequency usage rights | 3 years |
Carrying amount of the 28 gegahertz frequency usage [member] |  |
Disclosure of detailed information about intangible assets [line items] |  |
Impairment loss | ₩ 190,929 |
KT Skylife Co Ltd [member] | Intangible assets with indefinite useful life [member] |  |
Disclosure of detailed information about intangible assets [line items] |  |
Impairment loss | ₩ 0 |
Individual assets or cash-generating units [member] |  |
Disclosure of detailed information about intangible assets [line items] |  |
Impairment loss |  | ₩ 38,519
Discount rate |  | 7.30%

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- Definition The amount of acquisition-related costs recognised as an expense for transactions that are recognised separately from the acquisition of assets and the assumption of liabilities in business combinations. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2020-01-01 -Paragraph B64 -Subparagraph m -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IFRS&num=3&code=ifrs-tx-2020-en-r&anchor=para_B64_m&doctype=Appendix&subtype=B -URIDate 2020-01-01 + Details
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- Definition The discount rate used in the current measurement of fair value less costs of disposal. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2020-01-01 -Paragraph 130 -Subparagraph f -Clause iii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=36&code=ifrs-tx-2020-en-r&anchor=para_130_f_iii&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The amount recognised as a reduction of the carrying amount of an asset or cash-generating unit to its recoverable amount. [Refer: Carrying amount [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2020-01-01 -Paragraph 130 -Subparagraph b -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=36&code=ifrs-tx-2020-en-r&anchor=para_130_b&doctype=Standard -URIDate 2020-01-01 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 36 -IssueDate 2020-01-01 -Paragraph 130 -Subparagraph d -Clause ii -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=36&code=ifrs-tx-2020-en-r&anchor=para_130_d_ii&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The useful life, measured as period of time, used for intangible assets other than goodwill. [Refer: Intangible assets other than goodwill] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 38 -IssueDate 2020-01-01 -Paragraph 118 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=38&code=ifrs-tx-2020-en-r&anchor=para_118_a&doctype=Standard -URIDate 2020-01-01 + Details
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