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Subsequent Event - Agreement and Plan of Merger - Narrative (Details) - Alloy Parent and Alloy Merger Sub - Forecast $ / shares in Units, $ in Millions	8 Months Ended
	Dec. 31, 2024 USD ($) $ / shares
Subsequent Event
Subsequent Event [Line Items]
Conversion price, cash (in usd per share) | $ / shares	$ 67.00
Equity value of ALLETE common stock acquired	$ 3,900
Alloy Parent
Subsequent Event [Line Items]
Required amount to purchase of preferred stock	$ 300

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Price of a single share of a number of saleable stocks paid or offered to be paid in a business combination.

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Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer.

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Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event.

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