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Financial Instruments by Category - Summary of Gains or Losses Arising From Financial Instruments by Category (Parenthetical) (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2024 | Dec. 31, 2023 | Dec. 31, 2022
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income recognized as operating revenue | ₩ 303,535 | ₩ 279,607 | ₩ 271,925
Interest expense recognized as operating expense | 374,665 | 356,345 | 293,854
Profit and loss from foreign currency transaction | 27,268 | 27,407 | 67,976
BC Card Co., Ltd. [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income recognized as operating revenue | 106,005 | 112,973 | 68,869
Interest expense recognized as operating expense | 57,872 | 55,677 | 27,060
Profit and loss from foreign currency transaction | 10,298 | 5,597 | 3,569
Dividend income | 1,701 | 1,759 | 2,299
Gain (loss) on valuation | (576) | (11,112) | (7,860)
Gain (loss) on valuation of derivatives | 57 | 48 | ₩ (418)
KT Cloud Co., Ltd. [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain on convertible preferred stock | ₩ 317,178 | ₩ 311,312 |

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