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Business Combination - Schedule of Recognized Goodwill as a Result of Business Combination (Detail) - KRW (₩) ₩ in Millions | Dec. 31, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
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Disclosure of detailed information about business combination [Line Items] |  |  |  |
Add: Non-controllinginterests | ₩ 194 |  | ₩ 732 | ₩ (4,022)
SG Safety Corporation [member] |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |
Purchase consideration | 27,544 | ₩ 27,570 |  |
Less: Fair value of identifiable net assets | 12,126 |  |  |
Goodwill | 15,418 |  |  |
KT MOS Bukbu Co.,Ltd. [member] |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |
Purchase consideration | 8,160 |  |  |
Less: Fair value of identifiable net assets | 4,874 |  |  |
Goodwill | 3,286 |  |  |
KTMOS Nambu Co.,Ltd. [member] |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |
Purchase consideration | 6,310 |  |  |
Add: Non-controllinginterests | 101 |  |  |
Less: Fair value of identifiable net assets | 5,809 |  |  |
Goodwill | 602 |  |  |
CJ Digital Music Co., Ltd. [member] |  |  |  |
Disclosure of detailed information about business combination [Line Items] |  |  |  |
Purchase consideration | 50,948 |  |  |
Less: Fair value of identifiable net assets | 2,558 |  |  |
Goodwill | ₩ 48,390 |  |  |

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- Definition The fair value, at acquisition date, of the consideration transferred in a business combination. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph B64 -Subparagraph f -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_B64_f&doctype=Appendix&seq=2 -URIDate 2018-03-16 + Details
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- Definition The amount recognised as of the business combination's acquisition date for goodwill. [Refer: Goodwill; Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph B64 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_B64&doctype=Appendix&seq=2 -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph IE72 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_IE72&doctype=Illustrative%20Examples -URIDate 2018-03-16 + Details
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- Definition The amount recognised as of the acquisition date for net identifiable assets acquired or liabilities assumed in a business combination. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph B64 -Subparagraph i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_B64_i&doctype=Appendix&seq=2 -URIDate 2018-03-16 Reference 2: http://www.xbrl.org/2003/role/exampleRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph IE72 -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_IE72&doctype=Illustrative%20Examples -URIDate 2018-03-16 + Details
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- Definition The amount of non-controlling interest in the acquiree recognised at the acquisition date for business combinations in which the acquirer holds less than 100 per cent of the equity interests in the acquiree at the acquisition date. [Refer: Business combinations [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IFRS -Number 3 -IssueDate 2018-01-01 -Paragraph B64 -Subparagraph o -Clause i -URI http://eifrs.ifrs.org/eifrs/XBRL?type=IFRS&num=3&date=2018-03-01&anchor=para_B64_o_i&doctype=Appendix&seq=2 -URIDate 2018-03-16 + Details
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