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Other Financial Assets and Liabilities - Summary of Valuation Gains and Losses on Derivatives Contracts (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain |  | ₩ 77,275 | ₩ 66,305
Valuation loss | ₩ 163,710 | 15,829 | 2,045
Other comprehensive income | (113,742) | 91,521 | 21,651
Interest rate swap [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain |  |  | 192
Valuation loss |  | 45 |
Other comprehensive income | (567) | (963) | (488)
Currency swap [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain |  | 72,417 | 58,912
Valuation loss | 161,661 | 15,784 | 2,045
Other comprehensive income | (113,175) | 87,626 | 22,139
Currency forwards [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain |  | 4,858 | ₩ 7,201
Valuation loss | ₩ 2,049 |  |
Other comprehensive income |  | ₩ 4,858 |

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