Consolidated Statement of Income Unaudited - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Operating Revenue
Contracts with Customers – Utility	$ 314.3	$ 322.6	$ 919.1	$ 960.3
Contracts with Customers – Non-utility	63.2	64.5	554.1	178.3
Other – Non-utility	1.3	1.2	3.9	6.3
Total Operating Revenue	378.8	388.3	1,477.1	1,144.9
Operating Expenses
Fuel, Purchased Power and Gas – Utility	124.9	136.8	350.8	417.4
Transmission Services – Utility	22.7	19.3	66.3	57.5
Cost of Sales – Non-utility	33.0	38.4	436.7	96.9
Operating and Maintenance	83.6	83.2	254.2	238.1
Depreciation and Amortization	63.1	58.7	188.2	181.4
Taxes Other than Income Taxes	15.5	18.5	43.1	53.1
Total Operating Expenses	342.8	354.9	1,339.3	1,044.4
Operating Income	36.0	33.4	137.8	100.5
Other Income (Expense)
Interest Expense	(20.5)	(18.4)	(60.9)	(55.3)
Equity Earnings	4.7	2.3	16.1	13.1
Other	68.7	2.3	75.3	16.4
Total Other Income (Expense)	52.9	(13.8)	30.5	(25.8)
Income Before Income Taxes	88.9	19.6	168.3	74.7
Income Tax Expense (Benefit)	19.3	(7.2)	20.4	(19.4)
Net Income	69.6	26.8	147.9	94.1
Net Loss Attributable to Non-Controlling Interest	(16.3)	(6.9)	(47.7)	(43.5)
Net Income Attributable to ALLETE	$ 85.9	$ 33.7	$ 195.6	$ 137.6
Earnings Per Share [Abstract]
Basic (in shares)	57.4	57.1	57.3	55.5
Diluted (in shares)	57.5	57.2	57.4	55.6
Basic Earnings Per Share of Common Stock (in usd per share)	$ 1.50	$ 0.59	$ 3.41	$ 2.48
Diluted Earnings Per Share of Common Stock (in usd per share)	$ 1.49	$ 0.59	$ 3.41	$ 2.48