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Investments in Associates and Joint Ventures - Summary of Details of Associates (Detail) | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016
Disclosure of associates [line items] |  |
Date of financial statements | --12-31 |
K Bank Inc. [member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership | 10.00% |
Location | Korea |
Date of financial statements | --12-31 |
Korea Information & Technology Fund [member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership | 33.30% | 33.30%
Location | Korea |
Date of financial statements | --12-31 |
KT-SB Venture Investment [member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership | 50.00% | 50.00%
Location | Korea |
Date of financial statements | --12-31 |
Mongolian Telecommunications [Member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership |  | 40.00%
Location | Mongolia |
Date of financial statements | --12-31 |
KT Wibro Infra Co., Ltd. [member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership |  | 26.20%
Location | Korea |
Date of financial statements | --12-31 |
KT-IBKC future investment fund [member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership | 50.00% | 50.00%
Location | Korea |
Date of financial statements | --12-31 |
KT-CKP New Media Investment Fund [member] |  |
Disclosure of associates [line items] |  |
Percentage of ownership | 49.70% | 49.70%
Location | Korea |
Date of financial statements | --12-31 |

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- Definition The country in which an associate of the entity is incorporated. [Refer: Associates [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 16 -Subparagraph b -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_16_b_ii&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 17 -Subparagraph b -Clause ii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_17_b_ii&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph 21 -Subparagraph a -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_iii&doctype=Standard -URIDate 2017-03-09 + Details
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- Definition The proportion of ownership interest in an associate attributable to the entity. [Refer: Associates [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 17 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_17_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 27 -IssueDate 2017-01-01 -Paragraph 16 -Subparagraph b -Clause iii -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=27&date=2017-03-01&anchor=para_16_b_iii&doctype=Standard -URIDate 2017-03-09 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 12 -IssueDate 2017-01-01 -Paragraph 21 -Subparagraph a -Clause iv -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=12&date=2017-03-01&anchor=para_21_a_iv&doctype=Standard -URIDate 2017-03-09 + Details
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