Consolidated Statement of Comprehensive Income Unaudited - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Comprehensive Income [Abstract]
Net Income	$ 69.6	$ 26.8	$ 147.9	$ 94.1
Other Comprehensive Income (Loss)
Net of Income Tax Expense (Benefit) of $—, $—, $0.1 and $(0.2)	0.0	0.0	0.1	(0.4)
Net of Income Tax Expense (Benefit) of $—, $0.1, $(0.1) and $0.2	(0.1)	0.1	(0.2)	0.4
Total Other Comprehensive Income (Loss)	(0.1)	0.1	(0.1)	0.0
Total Comprehensive Income	69.5	26.9	147.8	94.1
Net Loss Attributable to Non-Controlling Interest	(16.3)	(6.9)	(47.7)	(43.5)
Total Comprehensive Income Attributable to ALLETE	$ 85.8	$ 33.8	$ 195.5	$ 137.6