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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income recognized as operating revenue | ₩ 244,796 | ₩ 93,078 | ₩ 115,686
Profit and loss from foreign currency transaction | 17,175 | 79,653 | 24,915
BC Card Co., Ltd. [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income recognized as operating revenue | 21,021 | 15,561 | 14,380
Profit and loss from foreign currency transaction | ₩ 20,422 | ₩ 11,049 | ₩ (1,987)

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