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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, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income recognized as operating revenue | ₩ 282,704 | ₩ 244,796 | ₩ 93,078
Interest expense recognized as operating expense | 268,225 | 296,874 | 302,464
Profit and loss from foreign currency transaction | 24,596 | 17,175 | 79,653
BC Card Co., Ltd. [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income recognized as operating revenue | 21,018 | 21,021 | 15,561
Interest expense recognized as operating expense | 548 | 21 | 0
Profit and loss from foreign currency transaction | 17,006 | 20,422 | 11,409
Operating expenses from foreign currency translation | ₩ 5 | ₩ 0 | ₩ 3

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