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Borrowings - Summary of Borrowings (Parenthetical) (Detail)
₩ in Millions
Dec. 31, 2017
KRW (₩)
Dec. 31, 2017
USD ($)
Dec. 31, 2016
KRW (₩)
Disclosure of detailed information about borrowings [Line Items]      
Borrowings | ₩ ₩ 6,683,662   ₩ 8,120,791
Libor rate 1.695% 1.695%  
Medium Term Note Programme [member] | Fixed interest rate [member]      
Disclosure of detailed information about borrowings [Line Items]      
Borrowings   $ 100,000,000  
Medium Term Note Programme [member] | Top of range [member] | Fixed interest rate [member]      
Disclosure of detailed information about borrowings [Line Items]      
Borrowings   $ 2,000,000,000