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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, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain | ₩ 66,305 | ₩ 57 | ₩ 109,436
Valuation loss | 2,045 | 209,582 | 138
Other comprehensive income | 21,651 | (146,508) | 85,483
Interest rate swap [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain | 192 | 38 |
Valuation loss |  |  | 148
Other comprehensive income | (488) | 637 | (142)
Currency swap [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain | 58,912 | 19 | 97,158
Valuation loss | 2,045 | 187,468 | (10)
Other comprehensive income | 22,139 | (146,752) | 85,479
Currency forwards [member] |  |  |
Disclosure of detailed information about financial instruments [line items] |  |  |
Valuation gain | ₩ 7,201 |  | 12,278
Valuation loss |  | 22,114 |
Other comprehensive income |  | ₩ (393) | ₩ 146

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