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Revenue from Contracts with Customers and Relevant Contract Assets and Liabilities - Detail Analysis of Contract with Customer Assets and Liabilities (Detail) - KRW (₩) ₩ in Millions | Dec. 31, 2018 | Jan. 01, 2018 | Dec. 31, 2017
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Disclosure of revenue from contracts with customers [line items] |  |  |
Deferred revenue | ₩ 39,528 |  | ₩ 23,036
Revenue from contracts with customers [member] |  |  |
Disclosure of revenue from contracts with customers [line items] |  |  |
Contract assets | 398,797 | ₩ 421,131 |
Contract liabilities | 347,461 | 282,836 |
Deferred revenue | ₩ 96,198 | ₩ 88,732 |

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- Definition The amount of an entity’s right to consideration in exchange for goods or services that the entity has transferred to a customer, when that right is conditioned on something other than the passage of time (for example, the entity’s future performance). + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 105 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_105&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 116 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_116_a&doctype=Standard -URIDate 2018-03-16 + Details
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Namespace Prefix: | ifrs-full_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition The amount of an entity’s obligation to transfer goods or services to a customer for which the entity has received consideration (or the amount is due) from the customer. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 105 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_105&doctype=Standard -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 15 -IssueDate 2018-01-01 -Paragraph 116 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=15&date=2018-03-01&anchor=para_116_a&doctype=Standard -URIDate 2018-03-16 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The amount of liability representing income that has been received but is not yet earned. [Refer: Revenue] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 1 -IssueDate 2018-01-01 -Paragraph 78 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=1&date=2018-03-01&anchor=para_78&doctype=Standard -URIDate 2018-03-16 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Disclosure of revenue from contracts with customers [line items] + References No definition available. + Details
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Namespace Prefix: | kt_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |