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Investments in Associates and Joint Ventures - Details of Investments in Associates (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
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Dec. 31, 2025 | Dec. 31, 2024
Disclosure of associates [line items] |  |  |
Investments in associates |  | ₩ 1,844,618 | ₩ 1,632,386
Domestic [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | ₩ 604,828 | 562,427
Domestic [member] | Samcheok Blue Power Co.,Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 4,507,138 |
Ownership (%) |  | 34.00% |
Investments in associates |  | ₩ 421,699 | ₩ 392,269
Domestic [member] | Chun-cheon Energy Co., Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 17,308,143 |
Ownership (%) |  | 49.10% | 49.10%
Investments in associates |  | ₩ 16,685 | ₩ 14,054
Domestic [member] | Pocheon-Hwado Highway Corp. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 7,109,230 |
Ownership (%) |  | 27.89% | 27.89%
Investments in associates |  | ₩ 17,194 | ₩ 14,834
Domestic [member] | CHUNGJU ENTERPRISE CITY DEVELOPMENT Co.,Ltd |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 944,920 |
Ownership (%) |  | 29.53% | 29.53%
Investments in associates |  | ₩ 12,096 | ₩ 12,401
Domestic [member] | PCC Amberstone Private Equity Fund I [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 3,077,195,168 |
Ownership (%) | [1] | 8.80% | 8.80%
Investments in associates |  | ₩ 2,791 | ₩ 6,181
Domestic [member] | Other associates [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 134,363 | 122,688
Domestic [member] | Acquisition cost [member] | Samcheok Blue Power Co.,Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 473,093 |
Domestic [member] | Acquisition cost [member] | Chun-cheon Energy Co., Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 86,541 |
Domestic [member] | Acquisition cost [member] | Pocheon-Hwado Highway Corp. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 35,546 |
Domestic [member] | Acquisition cost [member] | CHUNGJU ENTERPRISE CITY DEVELOPMENT Co.,Ltd |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 4,725 |
Domestic [member] | Acquisition cost [member] | PCC Amberstone Private Equity Fund I [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 3,077 |
Foreign [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | ₩ 1,239,790 | ₩ 1,069,959
Foreign [member] | South-East Asia Gas Pipeline Company Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 50,082 |
Ownership (%) |  | 25.04% | 25.04%
Investments in associates |  | ₩ 263,375 | ₩ 279,349
Foreign [member] | 9404-5515 Quebec Inc. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 284,463,243 |
Ownership (%) |  | 25.85% |
Investments in associates |  | ₩ 411,602 | ₩ 426,276
Foreign [member] | AMCI (WA) PTY LTD [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 49 |
Ownership (%) |  | 49.00% | 49.00%
Investments in associates |  | ₩ 162,606 | ₩ 68,478
Foreign [member] | KOREA LNG LTD. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 2,400 |
Ownership (%) |  | 20.00% | 20.00%
Investments in associates |  | ₩ 19,524 | ₩ 25,622
Foreign [member] | PT. Wampu Electric Power [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 8,708,400 |
Ownership (%) |  | 20.00% | 20.00%
Investments in associates |  | ₩ 16,483 | ₩ 17,680
Foreign [member] | POS-SeAH Steel Wire(Nantong) Co., Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 50 |
Ownership (%) |  | 25.00% | 25.00%
Investments in associates |  | ₩ 11,994 | ₩ 10,713
Foreign [member] | Other associates [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | ₩ 252,322 | ₩ 241,841
Foreign [member] | M RES NSW HCC II Pty Ltd [member] |  |  |
Disclosure of associates [line items] |  |  |
Number of shares |  | 72,000,000 |
Ownership (%) | [2],[3] | 92.31% | 0.00%
Investments in associates |  | ₩ 101,884 | ₩ 0
Foreign [member] | Acquisition cost [member] | South-East Asia Gas Pipeline Company Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 87,962 |
Foreign [member] | Acquisition cost [member] | 9404-5515 Quebec Inc. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 328,509 |
Foreign [member] | Acquisition cost [member] | AMCI (WA) PTY LTD [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 209,664 |
Foreign [member] | Acquisition cost [member] | KOREA LNG LTD. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 135,205 |
Foreign [member] | Acquisition cost [member] | PT. Wampu Electric Power [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 10,054 |
Foreign [member] | Acquisition cost [member] | POS-SeAH Steel Wire(Nantong) Co., Ltd. [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | 4,723 |
Foreign [member] | Acquisition cost [member] | M RES NSW HCC II Pty Ltd [member] |  |  |
Disclosure of associates [line items] |  |  |
Investments in associates |  | ₩ 104,511 |
[1] | The Company has determined that it has significant influence even though the Company’s percentage of ownership is less than 20% considering the composition of board of directors.
[2] | Although the Company holds a majority equity interest as of year-end, it has determined that it has significant influence considering its representation on the board of directors, and thus classified it as an investment in an associate.
[3] | During the year ended December 31, 2025, the entities were included as associates.

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