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General Information - Consolidated Subsidiaries Acquired or Newly Established (Detail)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Disclosure of subsidiaries [line items]    
Ownership (%) [1] 43.00% 43.00%
Total for all subsidiaries [member] | POSCO DEEPTECH IP FUND [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-06  
Ownership (%) 60.00%  
Reason New establishment  
Total for all subsidiaries [member] | FUTURE GRAPH CO., LTD. P&O Chemical Co., Ltd [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-06  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | CHEMGAS KOREA CO.,LTD.    
Disclosure of subsidiaries [line items]    
Date of addition 2025-07  
Ownership (%) 100.00%  
Reason Acquisition  
Total for all subsidiaries [member] | POSCO-EVER NEW MEDICAL Investment Fund [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-07  
Ownership (%) 60.00%  
Reason New establishment  
Total for all subsidiaries [member] | POSCO Stainless Precision & Processing [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-08  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | POSCO INTERNATIONAL CVC 1st Fund [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-08  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | POSCO CVC 1st Fund [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-08  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | New Zero 2nd Co., Ltd. [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-09  
Ownership (%) 100.00%  
Reason Acquisition  
Total for all subsidiaries [member] | POSCO DX CVC 1st Fund [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-09  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | POSCO Group AC Fund I [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-09  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | POSCO Safety Solution [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-09  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | Startup Korea Posco group Openinnovation Fund [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-11  
Ownership (%) 70.00%  
Reason New establishment  
Total for all subsidiaries [member] | POSCO INTERNATIONAL ALASKA ENERGY LLC [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-11  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | FLOW K CO., Ltd. [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-11  
Ownership (%) 70.00%  
Reason Transfer from associate to subsidiary  
Total for all subsidiaries [member] | POSCO FLOW VIETNAM CO LTD [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Ownership (%) 100.00%  
Reason New establishment  
Total for all subsidiaries [member] | PT Prime Agri Resources [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Ownership (%) 65.72%  
Reason Acquisition  
Total for all subsidiaries [member] | SANPU TRADING Co., Ltd. [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-05  
Reason Liquidation  
Total for all subsidiaries [member] | New Energy Hub [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-06  
Reason Merger  
Total for all subsidiaries [member] | POSCO CNGR Nickel Solution [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-07  
Reason Liquidation  
Total for all subsidiaries [member] | POSCO E&C Vietnam Co., Ltd. [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-08  
Reason Divestiture  
Total for all subsidiaries [member] | SK SOLRA POWER GENERATION COPORATION [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-08  
Reason Divestiture  
Total for all subsidiaries [member] | POSCO (Suzhou) Steel Processing Center CO., LTD [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-10  
Reason Liquidation  
Total for all subsidiaries [member] | SUZHOU POSCO-CORE TECHNOLOGY CO., LTD [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Reason Divestiture  
Total for all subsidiaries [member] | Mastern No.123 Yeoju Samgyo PFV CO., Ltd [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Reason Divestiture  
Total for all subsidiaries [member] | POSCO ENGINEERING & CONSTRUCTION DO BRAZIL LTDA. [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Reason Liquidation  
Total for all subsidiaries [member] | Consus Private Real Estate Fund 2 [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Reason Liquidation  
Total for all subsidiaries [member] | Consus Pf Private Real Estate Fund No.2 [Member]    
Disclosure of subsidiaries [line items]    
Date of addition 2025-12  
Reason Liquidation  
[1] As of December 31, 2025, the entities are classified as consolidated subsidiaries since the Company has control over the investees although the Company’s percentage of ownership is 50% or less, considering the structure of the entities’ Board of Directors and others.