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Financial Instruments by Category - Summary of Gains or Losses Arising From Financial Instruments by Category (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 | ₩ 282,704 | ₩ 244,796 | ₩ 93,078
Interest expense | (268,225) | (296,874) | (302,464)
Dividend income | 15,354 | 11,146 | 6,212
Total |  | (116,643) | (150,420)
Other comprehensive income (loss) for the year | 172,338 | (54,628) | (68,288)
Reclassified to profit or loss from other comprehensive income for the year | (44,684) | (44,279) |
Financial liabilities designated as at fair value through profit or loss [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain (loss) on disposal | 2,664 |  |
Gain (loss) on valuation | (1,936) |  |
Derivatives used for hedging [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain (loss) on transaction |  | 20,678 |
Gain (loss) on valuation | 4,949 | 42,195 | (145,885)
Other comprehensive income (loss) for the year | 20,742 | (2,810) | (66,624)
Reclassified to profit or loss from other comprehensive income for the year | (5,080) | (28,388) | 91,698
Financial liabilities at amortized cost [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest expense | (223,974) | (296,894) | (302,464)
Loss on repayment |  | (15) |
Gain (loss) foreign currency transaction | (20,958) | (30,956) | 62,347
Gain (loss) on foreign currency translation | (75,502) | (66,050) | 225,695
Total | 214,063 |  |
Financial assets at amortized cost [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income | 79,838 | 93,233 | 108,608
Gain (loss) foreign currency transaction | 32,293 | 19,396 | (11,949)
Gain (loss) on foreign currency translation | (474) | (2,901) | (12,354)
Gain (loss) on disposal | (43) | 44 | (20,351)
Gain (loss) on valuation | (59,947) | (110,544) | (44,219)
Financial assets at fair value through profit or loss [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income | 5,634 | 9,194 |
Dividend income | 1,096 | 1,207 |
Gain (loss) foreign currency transaction | (27) |  |
Gain (loss) on disposal | 5,115 | 1,713 |
Gain (loss) on valuation | 4,334 | 10,768 |
Financial assets at fair value through other comprehensive income [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income | 217,355 | 163,390 |
Dividend income | 2,312 | 1,704 |
Gain (loss) on disposal | (11,247) | (13,818) |
Impairment loss | (304) | (2,416) |
Other comprehensive income (loss) for the year | 167,152 | 43,811 |
Asset at fair value through profit or loss [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Dividend income |  |  | 1
Gain (loss) on disposal |  |  | 153
Gain (loss) on valuation |  |  | (464)
Derivative financial liabilities [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain (loss) on transaction | 6,332 | 7,272 | (58,569)
Gain (loss) on valuation | 56,537 | 22,065 | (63,640)
Other comprehensive income (loss) for the year | 46,806 | 20,078 | (44,429)
Reclassified to profit or loss from other comprehensive income for the year | ₩ (39,604) | (15,891) | 50,231
Available-for-sale [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Interest income |  |  | 453
Dividend income |  |  | 5,174
Gain (loss) on disposal |  |  | 89,598
Impairment loss |  |  | (6,137)
Other comprehensive income (loss) for the year |  |  | 51,235
Reclassified to profit or loss from other comprehensive income for the year |  |  | (55,450)
Held-to-maturity financial assets [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Gain (loss) on valuation |  | ₩ (2,708) | ₩ (3,078)

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