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Property, Plant and Equipment, Net - Changes in Carrying Amount of Property, Plant and Equipment (Parenthetical) (Detail) - KRW (₩)
₩ in Millions
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment loss on property plant and equipment ₩ 135,653 ₩ 608,122 ₩ 275,846
Steelmaking plant no.1 and Blast furnace no.4 [Member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment loss on property plant and equipment   227,239  
Anode/cathode material assets [Member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment loss on property plant and equipment   ₩ 307,911  
Finex Plant no. 3 [Member]      
Disclosure of detailed information about property, plant and equipment [line items]      
Impairment loss on property plant and equipment ₩ 69,988