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Investments in Associates and Joint Ventures - Details of Investments in Associates (Detail) - KRW (₩)
₩ in Millions

12 Months Ended

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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