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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, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Disclosure of subsidiaries [Line Items] |  |  |
Accumulated non-controlling interests at the beginning of the year | ₩ 1,352,844 |  |
Profit or loss allocated to non-controlling interests | 84,782 | ₩ 86,755 | ₩ 78,324
Accumulated non-controlling interests at the end of the year | ₩ 1,391,764 | ₩ 1,352,844 |
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 | ₩ 329,676 | ₩ 316,880 | ₩ 297,300
Profit or loss allocated to non-controlling interests | 9,395 | 22,445 | 27,032
Dividend paid to non-controlling interests | (9,817) | (8,279) | (8,325)
Others | (952) | (1,370) | 873
Accumulated non-controlling interests at the end of the year | ₩ 328,302 | ₩ 329,676 | ₩ 316,880
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 | ₩ 329,338 | ₩ 322,921 | ₩ 292,931
Profit or loss allocated to non-controlling interests | 43,961 | 47,068 | 62,943
Dividend paid to non-controlling interests | (29,490) | (44,637) | (22,650)
Others | (4,742) | 3,986 | (10,303)
Accumulated non-controlling interests at the end of the year | ₩ 339,067 | ₩ 329,338 | ₩ 322,921
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 | ₩ 51,751 | ₩ 50,926 | ₩ 70,231
Profit or loss allocated to non-controlling interests | 1,165 | 112 | (17,880)
Dividend paid to non-controlling interests |  |  | (1,118)
Others | 137 | 713 | (307)
Accumulated non-controlling interests at the end of the year | ₩ 53,053 | ₩ 51,751 | ₩ 50,926
KT Hitel Co., Ltd. [member] |  |  |
Disclosure of subsidiaries [Line Items] |  |  |
Non-controlling Interests rate(%) | 32.87% | 35.27% | 36.30%
Accumulated non-controlling interests at the beginning of the year | ₩ 51,798 | ₩ 50,689 | ₩ 51,136
Profit or loss allocated to non-controlling interests | 870 | 1,274 | (608)
Others | 478 | (165) | 161
Accumulated non-controlling interests at the end of the year | ₩ 53,146 | ₩ 51,798 | ₩ 50,689
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 | ₩ 103,532 | ₩ 103,428 | ₩ 104,821
Profit or loss allocated to non-controlling interests | 381 | 19 | (1,000)
Others | (445) | 85 | (393)
Accumulated non-controlling interests at the end of the year | ₩ 103,468 | ₩ 103,532 | ₩ 103,428

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