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Related Party Transactions - Summary of Fund Transactions with Related Parties (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | ₩ 255,302 | ₩ 25,603 | ₩ 24,713
Repayment | 20,304 | 30,385 |
PT. Mitra Transaksi Indonesia [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | 1,567
KT-IBKC future investment fund [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  | 3,750 | (1,050)
Korea Electronic Vehicle Charging Service [Member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | 168
Gyeonggi-KT Yoojin Superman Fund [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | 1,000 | 1,000 | 1,000
K-REALTY CR REIT [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Repayment |  | 30,385 |
K Bank Inc. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | 195,011 | 21,782 | 26,725
MOS GS Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (147)
MOS Daegu Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (147)
MOS Chungcheong Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (153)
MOS Gangnam Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (180)
MOS GB Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (203)
MOS BS Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (183)
MOS Honam Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (206)
PHI Healthcare Inc [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | 1,000
KT-CKP New Media Investment Fund [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | (109) | (174) | (1,229)
KT-DSC creative economy youth start-up investment fund [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  | (1,800) | (1,800)
GE Premier 1st Corporate Restructuring Real Estate Investment Trust Company [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | (3,423)
JB Emerging Market Specialty Investment Private Equity Trust No one[member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | 3,960
Boston Global Film Contents Fund Lp [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  |  | ₩ (986)
KT Philippines co. Ltd. {member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  | 99 |
Virtua Realm Sendirian Berhad [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  | 550 |
KT-Smart Factory Investment Fund [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | 2,800 | 2,800 |
KT-SB Venture Investment Fund [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash |  | ₩ (2,404) |
Studio Discovery Co Ltd [Member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | 3,000 |  |
KT Young Entrepreneurs DNA Investment Fund [Member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | 3,600 |  |
Hyundai Robotics Co Ltd [Member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Equity contributions in cash | 50,000 |  |
K-Realty CR-REITs No.1 [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Repayment | ₩ 20,304 |  |

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