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Related Party Transactions - Significant Financial Transactions Between the Company, Excluding the Controlling Company, and Related Parties (Detail) - KRW (₩) ₩ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2025 | Dec. 31, 2024 | Dec. 31, 2023
Disclosure of transactions between related parties [line items] |  |  |
Beginning | ₩ 581,267 | ₩ 510,570 | ₩ 532,515
Lend | 78,628 | 78,487 | 245,810
Collect | (100,546) | (70,961) | (280,605)
Others | 13,219 | 63,171 | 12,850
Ending | 572,568 | 581,267 | 510,570
UITrans LRT Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 51,051 | 46,335 | 36,510
Lend | 0 | 4,718 | 9,825
Collect | (11,718) |  | 0
Others | 0 | (2) | 0
Ending | 39,333 | 51,051 | 46,335
PT. Tanggamus Electric Power [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 3,854 | 4,826 | 5,014
Collect | (3,089) | (1,288) | (270)
Others | 1,823 | 316 | 82
Ending | 2,588 | 3,854 | 4,826
PT. Wampu Electric Power [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning |  | 0 | 3,988
Collect |  |  | (4,063)
Others |  |  | 75
Ending |  |  | 0
Nickel mining company SAS [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 68,793 | 64,197 | 63,024
Collect |  | 0 | (2,322)
Others | 7,064 | 4,596 | 3,495
Ending | 75,857 | 68,793 | 64,197
KRAKATAU POS-CHEM DONG-SUH CHEMICAL [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 1,470 | 2,579 | 3,802
Collect | (1,435) | (1,379) | (1,323)
Others | (35) | 270 | 100
Ending | 0 | 1,470 | 2,579
POS-SeAH Steel Wire (Thailand) Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning |  | 0 | 7,604
Collect |  |  | (7,828)
Others |  |  | 224
Ending |  |  | 0
AMCI (WA) PTY LTD [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 142,767 | 112,177 | 104,281
Lend | 73 | 6,499 | 6,620
Collect | (13,657) |  |
Others | 7,397 | 24,091 | 1,276
Ending | 136,580 | 142,767 | 112,177
POS-AUSTEM WUHAN AUTOMOTIVE CO.,LTD [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 5,636 | 5,158 | 10,138
Collect | (5,733) | 0 | (5,321)
Others | 97 | 478 | 341
Ending | 0 | 5,636 | 5,158
Hyo-chun Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 2,382 | 2,382 | 2,382
Ending | 2,382 | 2,382 | 2,382
POS-AUSTEM Suzhou Automotive Co., Ltd [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning |  | 0 | 12,673
Collect |  |  | (13,219)
Others |  |  | 546
Ending |  |  | 0
FQM Australia Holdings Pty Ltd [Member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 292,764 | 256,938 | 247,868
Lend | 0 | 3,126 | 2,637
Others | (173) | 32,700 | 6,433
Ending | 292,591 | 292,764 | 256,938
POHANG E&E Co., LTD |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 3,228 | 1,646 | 100
Lend | 1,444 | 1,582 | 1,546
Ending | 4,672 | 3,228 | 1,646
POSCO(Guangdong) Automotive Steel Co., Ltd. [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 6,162 | 14,332 | 35,131
Lend | 64,858 | 59,402 | 225,182
Collect | (64,914) | (68,294) | (246,259)
Others | 106 | 722 | 278
Ending | 6,212 | 6,162 | ₩ 14,332
Gale International Korea, LLC [member] |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 100 |  |
Lend | 344 | 100 |
Ending | 444 | 100 |
P&O Chemical Co., Ltd |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Beginning | 3,060 |  |
Lend | 0 | 3,060 |
Others | (3,060) |  |
Ending | 0 | ₩ 3,060 |
POS-AUSTEM Suzhou Automotive |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Lend | 6,143 |  |
Ending | 6,143 |  |
CAML |  |  |
Disclosure of transactions between related parties [line items] |  |  |
Lend | 5,766 |  |
Ending | ₩ 5,766 |  |

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