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AGREEMENT AND PLAN OF MERGER (Details) - Alloy Parent and Alloy Merger Sub $ / shares in Units, $ in Millions | May 05, 2024 USD ($) day $ / shares | Sep. 30, 2025 USD ($)
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Subsequent Event [Line Items] |  |
Conversion price, cash (in usd per share) | $ / shares | $ 67.00 |
Equity value of ALLETE common stock acquired | $ 3,900 |
Maximum conversion window | day | 5 |
Alloy Parent | Forecast |  |
Subsequent Event [Line Items] |  |
Required amount to purchase of preferred stock |  | $ 300

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