Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Comprehensive Income [Abstract]
Net Income	$ 26.8	$ 24.1	$ 94.1	$ 89.2
Other Comprehensive Income (Loss) [Abstract]
Unrealized Loss on Securities - Net of Income Tax Expense $-, $-, $(0.2) and $-	0.0	0.0	(0.4)	0.0
Defined Benefit Pension and Other Postretirement Benefit Plans - Net of Income Tax Expense of $0.1, $0.1, $0.2 and $0.4	0.1	0.4	0.4	1.2
Total Other Comprehensive Income (Loss)	0.1	0.4	0.0	1.2
Total Comprehensive Income	26.9	24.5	94.1	90.4
Net Loss Attributable to Non-Controlling Interest	(6.9)	(3.5)	(43.5)	(18.1)
Total Comprehensive Income Attributable to ALLETE	$ 33.8	$ 28.0	$ 137.6	$ 108.5