Consolidated Statement of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Consolidated Statement of Income [Abstract]
Operating Revenue	$ 240.0	$ 242.2
Operating Expenses [Abstract]
Fuel and Purchased Power	77.1	79.0
Operating and Maintenance	99.9	90.1
Depreciation	24.6	22.3
Total Operating Expenses	201.6	191.4
Operating Income	38.4	50.8
Other Income (Expense) [Abstract]
Interest Expense	(11.0)	(10.7)
Equity Earnings in ATC	4.6	4.4
Other	0.7	0.8
Total Other Expense	(5.7)	(5.5)
Income Before Non-Controlling Interest and Income Taxes	32.7	45.3
Income Tax Expense	8.3	8.2
Net Income	24.4	37.1
Less: Non-Controlling Interest in Subsidiaries	0	(0.1)
Net Income Attributable to ALLETE	$ 24.4	$ 37.2
Average Shares of Common Stock [Abstract]
Basic	36.8	34.6
Diluted	36.9	34.7
Basic Earnings Per Share of Common Stock	$ 0.66	$ 1.07
Diluted Earnings Per Share of Common Stock	$ 0.66	$ 1.07
Dividends Per Share of Common Stock	$ 0.46	$ 0.445