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Asset Retirement Obligations (Tables) | 12 Months Ended
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Dec. 31, 2025
Asset Retirement Obligation Disclosure [Abstract] |
Change in Asset Retirement Obligations | The following table summarizes the change in AROs. Amounts include conditional AROs.
(In thousands) |  | 2025 |  |  | 2024 |
Balance as of January 1, |  | $ | 69,132 |  |  | $ | 54,430 |
Liabilities incurred(a) |  |  | 3,010 |  |  |  | 25,756 |
Accretion expense |  |  | 3,435 |  |  |  | 2,671 |
Liabilities settled(b) |  |  | (808 | ) |  |  | (7,548 | )
Revisions in estimated cash flows(c) |  |  | 1,520 |  |  |  | (6,177 | )
Balance as of December 31, |  | $ | 76,289 |  |  | $ | 69,132 |
(a) In June 2024, MGE recorded an asset retirement obligation for its estimated share of the legal liability associated with the effect of the CCR Legacy Rule for remediation and groundwater compliance monitoring at Columbia. See Footnote 16 for further information on the CCR Legacy Rule. (b) In 2024, MGE settled $6.8 million of liabilities related to the Columbia Ash Pond. (c) In December 2024, revisions were made related to the Columbia CCR asset retirement obligation estimates based on additional analysis completed on the impacted areas.

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- Definition Tabular disclosure of the changes in carrying amount of a liability for asset retirement obligations, for changes such as new obligations, changes in estimates of existing obligations, spending on existing obligations, property dispositions, and foreign currency translation. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (c) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-1 + Details
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