CONSOLIDATED STATEMENT OF EQUITY Unaudited - USD ($) $ in Millions	Total	Common Stock	Accumulated Other Comprehensive Loss	Retained Earnings	Non-Controlling Interest in Subsidiaries
Balance, Beginning of Period at Dec. 31, 2023		$ 1,803.7	$ (20.5)	$ 1,026.4	$ 597.0
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued		10.1
Defined Benefit Pension and Other Postretirement Benefit Plans	$ (0.4)		(0.4)
Net Income Attributable to ALLETE	83.7			83.7
Common Stock Dividends				(81.3)
Proceeds from Non-Controlling Interest in Subsidiaries – Net					1.4
Net Loss Attributable to Non-Controlling Interest	27.0				(24.7)
Distributions to Non-Controlling Interest					(0.7)
Balance, End of Period at Jun. 30, 2024	3,394.7	1,813.8	(20.9)	1,028.8	573.0
Balance, Beginning of Period at Dec. 31, 2023	0.5
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	2.7
Net Income (Loss) Attributable to Non-Controlling Interest	(2.3)
Total Redeemable Non-Controlling Interest at Jun. 30, 2024	$ 0.9
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 1.41
Balance, Beginning of Period at Mar. 31, 2024		1,807.4	(20.9)	1,036.5	585.5
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued		6.4
Defined Benefit Pension and Other Postretirement Benefit Plans	$ 0.0
Net Income Attributable to ALLETE	33.0			33.0
Common Stock Dividends				(40.7)
Proceeds from Non-Controlling Interest in Subsidiaries – Net					1.4
Net Loss Attributable to Non-Controlling Interest	13.3				(13.7)
Distributions to Non-Controlling Interest					(0.2)
Balance, End of Period at Jun. 30, 2024	3,394.7	1,813.8	(20.9)	1,028.8	573.0
Balance, Beginning of Period at Mar. 31, 2024	0.5
Redeemable Non-Controlling Interest
Net Income (Loss) Attributable to Non-Controlling Interest	0.4
Total Redeemable Non-Controlling Interest at Jun. 30, 2024	$ 0.9
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 0.705
Balance, Beginning of Period at Dec. 31, 2024	$ 3,390.1	1,823.2	(18.1)	1,042.9	542.1
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued		10.5
Defined Benefit Pension and Other Postretirement Benefit Plans	0.0
Net Income Attributable to ALLETE	88.0			88.0
Common Stock Dividends				(84.6)
Proceeds from Non-Controlling Interest in Subsidiaries – Net					2.0
Net Loss Attributable to Non-Controlling Interest	46.7				(39.3)
Distributions to Non-Controlling Interest					(0.4)
Balance, End of Period at Jun. 30, 2025	3,366.3	1,833.7	(18.1)	1,046.3	504.4
Balance, Beginning of Period at Dec. 31, 2024	0.4
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	7.9
Net Income (Loss) Attributable to Non-Controlling Interest	(7.4)
Distributions to Non-Controlling Interest	(0.1)
Total Redeemable Non-Controlling Interest at Jun. 30, 2025	$ 0.8
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 1.46
Balance, Beginning of Period at Mar. 31, 2025		1,827.4	(18.1)	1,056.7	522.3
Consolidated Statement of Equity [Roll Forward]
Common Stock Issued		6.3
Defined Benefit Pension and Other Postretirement Benefit Plans	$ 0.0
Net Income Attributable to ALLETE	31.9			31.9
Common Stock Dividends				(42.3)
Net Loss Attributable to Non-Controlling Interest	25.3				(17.8)
Distributions to Non-Controlling Interest					(0.1)
Balance, End of Period at Jun. 30, 2025	3,366.3	$ 1,833.7	$ (18.1)	$ 1,046.3	$ 504.4
Balance, Beginning of Period at Mar. 31, 2025	0.5
Redeemable Non-Controlling Interest
Proceeds from Non-Controlling Interest in Subsidiaries	7.9
Net Income (Loss) Attributable to Non-Controlling Interest	(7.5)
Distributions to Non-Controlling Interest	(0.1)
Total Redeemable Non-Controlling Interest at Jun. 30, 2025	$ 0.8
Redeemable Non-Controlling Interest
Dividends Per Share of Common Stock (in usd per share)	$ 0.73