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Other Financial Assets and Liabilities - Summary of Hedging instruments (Detail) - Derivatives [member] - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Disclosure of detailed information about hedging instruments [line items]    
Contract amount ₩ 2,771,700 ₩ 2,616,123
Assets 7,684 58,576
Liabilities 127,929 20,096
Changes in fair value to calculate the ineffective portion of hedges (154,528) 64,876
USD    
Disclosure of detailed information about hedging instruments [line items]    
Foreign currency 1,768,912 1,574,068
Contract amount 2,037,568 1,788,831
Assets 2,111 30,175
Liabilities 100,623 10,692
Changes in fair value to calculate the ineffective portion of hedges (136,852) 49,480
JPY    
Disclosure of detailed information about hedging instruments [line items]    
Foreign currency 46,000,000 80,000,000
Contract amount 488,924 827,292
Assets 5,573 28,401
Liabilities 13,839 9,404
Changes in fair value to calculate the ineffective portion of hedges (4,065) ₩ 15,396
SGD    
Disclosure of detailed information about hedging instruments [line items]    
Foreign currency 284,000  
Contract amount 245,208  
Liabilities 13,467  
Changes in fair value to calculate the ineffective portion of hedges ₩ (13,611)