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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, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of subsidiaries [line items] |  |  |
Accumulated non-controlling interests at the beginning of the year | ₩ 1,528,589 |  |
Profit or loss allocated to non-controlling interests | 50,165 | ₩ 73,841 | ₩ 84,782
Accumulated non-controlling interests at the end of the year | ₩ 1,520,160 | ₩ 1,528,589 |
KT Skylife Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 49.73% | 49.73% | 49.73%
Accumulated non-controlling interests at the beginning of the year | ₩ 374,150 | ₩ 328,302 | ₩ 329,676
Profit or loss allocated to non-controlling interests | 10,029 | 23,405 | 9,395
Dividend paid to non-controlling interests | (8,279) | (8,279) | (9,817)
Others | 6 | 30,722 | (952)
Accumulated non-controlling interests at the end of the year | ₩ 375,906 | ₩ 374,150 | ₩ 328,302
BC Card Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 30.46% | 30.46% | 30.46%
Accumulated non-controlling interests at the beginning of the year | ₩ 345,547 | ₩ 339,067 | ₩ 329,338
Profit or loss allocated to non-controlling interests | 37,795 | 28,418 | 43,961
Dividend paid to non-controlling interests | (18,900) | (35,924) | (29,490)
Others | 53,033 | 13,986 | (4,742)
Accumulated non-controlling interests at the end of the year | ₩ 417,475 | ₩ 345,547 | ₩ 339,067
KT Powertel Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 55.15% | 55.15% | 55.15%
Accumulated non-controlling interests at the beginning of the year | ₩ 52,865 | ₩ 53,053 | ₩ 51,751
Profit or loss allocated to non-controlling interests | 1,751 | (3,058) | 1,165
Others | (340) | 2,870 | 137
Accumulated non-controlling interests at the end of the year | ₩ 54,276 | ₩ 52,865 | ₩ 53,053
KT Hitel Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 32.87% | 32.87% | 32.87%
Accumulated non-controlling interests at the beginning of the year | ₩ 52,336 | ₩ 53,146 | ₩ 51,798
Profit or loss allocated to non-controlling interests | 1,720 | 454 | 870
Others | 653 | (1,264) | 478
Accumulated non-controlling interests at the end of the year | ₩ 54,709 | ₩ 52,336 | ₩ 53,146
KT Telecop Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [line items] |  |  |
Non-controlling Interests rate(%) | 13.18% | 13.18% | 13.18%
Accumulated non-controlling interests at the beginning of the year | ₩ 103,357 | ₩ 103,468 | ₩ 103,532
Profit or loss allocated to non-controlling interests | (588) | 59 | 381
Others | (99,119) | (170) | (445)
Accumulated non-controlling interests at the end of the year | ₩ 3,650 | ₩ 103,357 | ₩ 103,468

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