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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
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