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Asset Retirement Obligations | 12 Months Ended
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Dec. 31, 2025
Asset Retirement Obligation Disclosure [Abstract] |
Asset Retirement Obligation Disclosure [Text Block] | Asset Retirement Obliga tions - MGE Energy and MGE. MGE recorded an obligation for the fair value of its legal liability for asset retirement obligations (AROs) associated with removal of the West Campus Cogeneration Facility and the Elm Road Units, electric substations, combustion turbine generating units, wind generating facilities, solar generating facilities, and battery storage, all of which are located on property not owned and would need to be removed upon the ultimate end of the associated leases. The significant conditional AROs identified by MGE included the costs of abandoning in place gas services and mains, the abatement and disposal of equipment and buildings contaminated with asbestos and PCBs, and the proper disposal and removal of tanks, batteries, and underground cable. Changes in management's assumptions regarding settlement dates, settlement methods, or assigned probabilities could have a material effect on the liabilities and the associated regulatory asset recorded as of December 31, 2025. MGE also may have AROs relating to the removal of various assets, such as certain electric and gas distribution facilities. These facilities are generally located on property owned by third parties, on which MGE is permitted to operate by lease, permit, easement, license, or service agreement. The asset retirement obligations associated with these facilities cannot be reasonably determined due to the indeterminate life of the related agreements. 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 The entire disclosure for an asset retirement obligation and the associated long-lived asset. An asset retirement obligation is a legal obligation associated with the disposal or retirement from service of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Subparagraph (a) -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 410 -SubTopic 20 -Name Accounting Standards Codification -Publisher FASB -URI https://asc.fasb.org/410-20/tableOfContent Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Name Accounting Standards Codification -Section 50 -Paragraph 2 -SubTopic 20 -Topic 410 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481850/410-20-50-2 + Details
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