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Information About Non-controlling Interests - Summary of Changes in Accumulated Non-controlling Interests (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of subsidiaries [line items] |  |  |
Accumulated non-controlling interests at the beginning of the year | ₩ 1,520,160 |  |
Profit or loss allocated to non-controlling interests | 45,367 | ₩ 50,165 | ₩ 73,841
Accumulated non-controlling interests at the end of the year | ₩ 1,539,989 | ₩ 1,520,160 |
KT Skylife Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 49.70% | 49.70% | 49.70%
Accumulated non-controlling interests at the beginning of the year | ₩ 375,906 | ₩ 374,150 | ₩ 328,302
Profit or loss allocated to non-controlling interests | 22,171 | 10,029 | 23,405
Dividend paid to non-controlling interests | (8,279) | (8,279) | (8,279)
Others | (898) | 6 | 30,722
Accumulated non-controlling interests at the end of the year | ₩ 388,900 | ₩ 375,906 | ₩ 374,150
BC Card Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 30.50% | 30.50% | 30.50%
Accumulated non-controlling interests at the beginning of the year | ₩ 417,475 | ₩ 345,547 | ₩ 339,067
Profit or loss allocated to non-controlling interests | 9,899 | 37,795 | 28,418
Dividend paid to non-controlling interests | (22,787) | (18,900) | (35,924)
Others | 7,239 | 53,033 | 13,986
Accumulated non-controlling interests at the end of the year | ₩ 411,826 | ₩ 417,475 | ₩ 345,547
KT Powertel Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 55.20% | 55.20% | 55.20%
Accumulated non-controlling interests at the beginning of the year | ₩ 54,276 | ₩ 52,865 | ₩ 53,053
Profit or loss allocated to non-controlling interests | 2,151 | 1,751 | (3,058)
Dividend paid to non-controlling interests | (478) |  |
Others | (202) | (340) | 2,870
Accumulated non-controlling interests at the end of the year | ₩ 55,747 | ₩ 54,276 | ₩ 52,865
KT Hitel Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 32.90% | 32.90% | 32.90%
Accumulated non-controlling interests at the beginning of the year | ₩ 54,709 | ₩ 52,336 | ₩ 53,146
Profit or loss allocated to non-controlling interests | (1,840) | 1,720 | 454
Others | (2,563) | 653 | (1,264)
Accumulated non-controlling interests at the end of the year | ₩ 50,306 | ₩ 54,709 | ₩ 52,336
KT Telecop Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 13.20% | 13.20% | 13.20%
Accumulated non-controlling interests at the beginning of the year | ₩ 3,650 | ₩ 103,357 | ₩ 103,468
Profit or loss allocated to non-controlling interests | 152 | (588) | 59
Others | (208) | (99,119) | (170)
Accumulated non-controlling interests at the end of the year | ₩ 3,594 | ₩ 3,650 | ₩ 103,357

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