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Commitments and Contingencies - Summary of SOC Projects (Detail)
₩ in Millions
Dec. 31, 2025
KRW (₩)
Disclosure of contingent liabilities [line items]  
Approved amount ₩ 2,486,755
Remaining balance after repayment 1,395,830
SOC Projects [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 3,472,663
Remaining balance after repayment 2,057,062
Associates and joint ventures [member] | SOC Projects [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 537,617
Remaining balance after repayment 397,661
Associates and joint ventures [member] | SOC Projects [member] | POSCO DX Co., Ltd. [member] | Pocheon-Hwado Highway Corp. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 24,923
Remaining balance after repayment 22,234
Associates and joint ventures [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Pocheon-Hwado Highway Corp. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 319,515
Remaining balance after repayment 285,039
Associates and joint ventures [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Pohang E&E Co,. Ltd. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 71,930
Remaining balance after repayment 39,266
Associates and joint ventures [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Pureun Tongyeong Enviro Co., Ltd. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 25,630
Remaining balance after repayment 9,804
Associates and joint ventures [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Pure Gimpo Co., Ltd. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 51,565
Remaining balance after repayment 21,181
Associates and joint ventures [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Clean Iksan Co., Ltd. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 44,054
Remaining balance after repayment 20,137
Others [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 1,947,125
Remaining balance after repayment 1,036,505
Others [member] | SOC Projects [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 2,935,046
Remaining balance after repayment 1,659,401
Others [member] | SOC Projects [member] | POSCO DX Co., Ltd. [member] | Western Inland highway CO.,LTD. [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 47,348
Remaining balance after repayment 32,668
Others [member] | SOC Projects [member] | POSCO DX Co., Ltd. [member] | Busan Sanseong Tunnel [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 7,621
Remaining balance after repayment 7,621
Others [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Western Seoul highway CO.,LTD. and others [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 63,683
Remaining balance after repayment 28,201
Others [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Western Inland highway CO.,LTD. and others [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 2,778,848
Remaining balance after repayment 1,562,721
Others [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Pohang Youngil Bay New Port [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 2,250
Remaining balance after repayment 1,440
Others [member] | SOC Projects [member] | POSCO Eco & Challenge Co., Ltd. (formerly, POSCO ENGINEERING & CONSTRUCTION CO.,LTD.) [member] | Busan Sanseong Tunnel [member]  
Disclosure of contingent liabilities [line items]  
Approved amount 35,296
Remaining balance after repayment ₩ 26,750