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Investments in Associates and Joint Ventures - Details of Investments in Joint Ventures (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | ₩ 3,135,535 | ₩ 3,106,407
PT NICOLE METAL INDUSTRY [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 62,574 |
Domestic [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | ₩ 161,104 | 201,927
Domestic [member] | POSCO MC MATERIALS (formerly, POSCO MITSUBISHI CARBON TECHNOLOGY) [member] |  |
Disclosure of joint ventures [line items] |  |
Number of shares | 11,568,000 |
Ownership (%) | 60.00% |
Investments in joint ventures | ₩ 146,038 | ₩ 153,839
Domestic [member] | SNNC [member] |  |
Disclosure of joint ventures [line items] |  |
Number of shares | 18,130,000 |
Ownership (%) | 49.00% | 49.00%
Investments in joint ventures | ₩ 2,364 | ₩ 38,046
Domestic [member] | Other joint ventures [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 12,702 | 10,042
Domestic [member] | Acquisition cost [member] | POSCO MC MATERIALS (formerly, POSCO MITSUBISHI CARBON TECHNOLOGY) [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 115,680 |
Domestic [member] | Acquisition cost [member] | SNNC [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 90,650 |
Foreign [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | ₩ 2,974,431 | ₩ 2,904,480
Foreign [member] | Roy Hill Holdings Pty Ltd. [member] |  |
Disclosure of joint ventures [line items] |  |
Number of shares | 13,117,972 |
Ownership (%) | 12.50% | 12.50%
Investments in joint ventures | ₩ 1,441,376 | ₩ 1,397,824
Foreign [member] | POSCO-NPS Niobium LLC [member] |  |
Disclosure of joint ventures [line items] |  |
Number of shares | 325,050,000 |
Ownership (%) | 50.00% | 50.00%
Investments in joint ventures | ₩ 466,492 | ₩ 477,898
Foreign [member] | KOBRASCO [member] |  |
Disclosure of joint ventures [line items] |  |
Number of shares | 2,010,719,185 |
Ownership (%) | 50.00% | 50.00%
Investments in joint ventures | ₩ 126,943 | ₩ 119,820
Foreign [member] | BX STEEL POSCO Cold Rolled Sheet Co., Ltd. [member] |  |
Disclosure of joint ventures [line items] |  |
Ownership (%) | 25.00% | 25.00%
Investments in joint ventures | ₩ 132,616 | ₩ 126,906
Foreign [member] | PT NICOLE METAL INDUSTRY [member] |  |
Disclosure of joint ventures [line items] |  |
Number of shares | 152,764,706 |
Ownership (%) | 49.00% | 49.00%
Investments in joint ventures | ₩ 649,462 | ₩ 578,604
Foreign [member] | HBIS-POSCO Automotive Steel Co.,Ltd |  |
Disclosure of joint ventures [line items] |  |
Ownership (%) | 50.00% | 50.00%
Investments in joint ventures | ₩ 134,404 | ₩ 179,841
Foreign [member] | Other joint ventures [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 23,138 | ₩ 23,587
Foreign [member] | Acquisition cost [member] | Roy Hill Holdings Pty Ltd. [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 1,528,672 |
Foreign [member] | Acquisition cost [member] | POSCO-NPS Niobium LLC [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 364,609 |
Foreign [member] | Acquisition cost [member] | KOBRASCO [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 32,950 |
Foreign [member] | Acquisition cost [member] | BX STEEL POSCO Cold Rolled Sheet Co., Ltd. [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 61,961 |
Foreign [member] | Acquisition cost [member] | PT NICOLE METAL INDUSTRY [member] |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | 603,178 |
Foreign [member] | Acquisition cost [member] | HBIS-POSCO Automotive Steel Co.,Ltd |  |
Disclosure of joint ventures [line items] |  |
Investments in joint ventures | ₩ 235,251 |

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