CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME Unaudited - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023
Statement of Comprehensive Income [Abstract]
Net Income	$ 32.7	$ 69.6	$ 89.4	$ 147.9
Other Comprehensive Loss
Unrealized Gain on Securities: Net of Income Tax Expense of $—, $—, $— and $0.1	0.1	0.0	0.1	0.1
Defined Benefit Pension and Other Postretirement Benefit Plans: Net of Income Tax Benefit of $(0.1), $—, $(0.3) and $(0.1)	(0.2)	(0.1)	(0.6)	(0.2)
Total Other Comprehensive Loss	(0.1)	(0.1)	(0.5)	(0.1)
Total Comprehensive Income	32.6	69.5	88.9	147.8
Net Loss Attributable to Non-Controlling Interest	(12.3)	(16.3)	(39.3)	(47.7)
Total Comprehensive Income Attributable to ALLETE	$ 44.9	$ 85.8	$ 128.2	$ 195.5