CONSOLIDATED STATEMENT OF COMPREHENSIVE INCOME Unaudited - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Statement of Comprehensive Income [Abstract]
Net Income	$ 19.7	$ 40.7	$ 56.7	$ 78.3
Other Comprehensive Income (Loss)
Net of Income Tax Expense of $—, $—, $— and $0.1	0.0	0.0	0.0	0.1
Defined Benefit Pension and Other Postretirement Benefit Plans; Net of Income Tax Benefit of $(0.3), $(0.1), $(0.2) and $(0.1)	0.0	(0.1)	(0.4)	(0.1)
Total Other Comprehensive Loss	0.0	(0.1)	(0.4)	0.0
Total Comprehensive Income	19.7	40.6	56.3	78.3
Net Loss Attributable to Non-Controlling Interest	(13.3)	(10.8)	(27.0)	(31.4)
Total Comprehensive Income Attributable to ALLETE	$ 33.0	$ 51.4	$ 83.3	$ 109.7