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Property, Plant and Equipment (Tables) | 12 Months Ended
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Dec. 31, 2024
Property, Plant and Equipment [Abstract] |
Property, Plant and Equipment and Estimated Useful Lives of Property, Plant and Equipment |
Property, Plant and Equipment |  |  |
As of December 31 | 2024 |  | 2023
Millions |  |  |
Regulated Operations |  |  |
Property, Plant and Equipment in Service | $5,387.8 |  |  | $5,167.2 |
Construction Work in Progress | 197.5 |  |  | 146.7 |
Accumulated Depreciation | (2,077.8) |  |  | (1,969.4) |
Regulated Operations – Net | 3,507.5 |  |  | 3,344.5 |
ALLETE Clean Energy |  |  |
Property, Plant and Equipment in Service | 1,605.3 |  |  | 1,612.8 |
Construction Work in Progress | 51.9 |  |  | 48.9 |
Accumulated Depreciation | (272.9) |  |  | (229.1) |
ALLETE Clean Energy – Net | 1,384.3 |  |  | 1,432.6 |
Corporate and Other (a) |  |  |
Property, Plant and Equipment in Service | 377.4 |  |  | 355.8 |
Construction Work in Progress | 77.5 |  |  | 27.5 |
Accumulated Depreciation | (165.2) |  |  | (147.0) |
Corporate and Other – Net | 289.7 |  |  | 236.3 |
Property, Plant and Equipment – Net | $5,181.5 |  |  | $5,013.4 |
(a)Primarily includes BNI Energy and a small amount of non-rate base generation.
Estimated Useful Lives of Property, Plant and Equipment (Years)
Regulated Operations |  |  |  |
Generation | 3 to 50 |  | ALLETE Clean Energy | 5 to 35
Transmission | 50 to 75 |  | Corporate and Other | 3 to 50
Distribution | 18 to 70 |  |  |
Asset Retirement Obligations | (a) The increase in liabilities recognized in 2024 reflects the impact of estimated compliance costs related to the EPA’s CCR Legacy Impoundment Rule finalized in May 2024. (See Note 9. Commitments, Guarantees and Contingencies.)

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- Definition Tabular disclosure of physical assets used in the normal conduct of business and not intended for resale. Includes, but is not limited to, balances by class of assets, depreciation and depletion expense and method used, including composite depreciation, and accumulated deprecation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Section 50 -Paragraph 1 -SubTopic 10 -Topic 360 -Publisher FASB -URI https://asc.fasb.org/1943274/2147482099/360-10-50-1 + Details
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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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