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Acquisitions (Details) - New Energy - USD ($) $ in Millions |  | 6 Months Ended | 9 Months Ended
--- | --- | --- | ---
Apr. 15, 2022 | Sep. 30, 2022 | Sep. 30, 2022
Business Acquisition [Line Items] |  |  |  |
Business Acquisition, Percentage of Voting Interests Acquired |  | 100.00% |  |
Transaction Purchase Price |  | $ 165.5 |  |
Business Combination, Consideration Transferred |  | 158.8 |  |
Business Acquisition, Pro Forma Information, Description |  |  |  | The Company has not presented separate results of operations since closing or combined pro forma financial information of the Company and New Energy since the beginning of 2021, as the results of operations for New Energy are not material to the Company's consolidated financials.
Business Combination, Reason for Business Combination |  |  |  | The acquisition of New Energy is consistent with ALLETE’s stated strategy of additional investment in renewable energy and related infrastructure across North America to support the Company’s sustainability-in-action strategy while providing potential long-term earnings growth.
Business Combination, Goodwill Recognized, Description |  |  |  | The goodwill recorded is primarily attributable to the highly skilled workforce of New Energy and synergies expected to arise as a result of the acquisition.
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual |  |  | $ 39.9 |
Cash and Equivalents |  | 3.9 |  |
Account Receivable |  | 1.4 |  |
Inventory | [1] | 25.3 |  |
Other Current Assets |  | 12.6 |  |
Property, Plant, and Equipment |  | 16.4 |  |
Goodwill | [2] | 155.1 |  |
Other Noncurrent Assets |  | 2.1 |  |
Total Assets Acquired |  | 216.8 |  |
Current Liabilities |  | 23.6 |  |
Long-Term Debt Due Within One Year |  | 28.3 |  |
Long-Term Debt |  | 5.9 |  |
Other Non-Current Liabilities |  | 0.2 |  |
Total Liabilities Assumed |  | 58.0 |  |
Net Identifiable Assets Acquired |  | 158.8 |  |
Business Acquisition, Goodwill, Expected Tax Deductible Amount |  | 155.1 |  |
Business Combination, Acquisition Related Costs |  |  |  | $ 2.6
Goodwill, Purchase Accounting Adjustments |  |  |  | 4.8
Finite-Lived Intangible Assets, Purchase Accounting Adjustments |  |  |  | 1.4
Net Liabilities Change - Purchase Accounting Adjustments |  |  |  | $ 6.2
Business Combinations, Fair Value Adjustments |  | $ 11.6 |  |
[1] | Includes $11.6 million of purchase price accounting for certain projects under development at the time of acquisition.
[2] | For tax purpose, the purchase price allocation resulted in $155.1 million of deductible goodwill

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