Consolidated Statement of Income (USD $) In Millions, except Per Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Consolidated Statement of Income [Abstract]
Operating Revenue	$ 226.9	$ 224.1	$ 689.0	$ 668.9
Operating Expenses [Abstract]
Fuel and Purchased Power	74.8	79.0	229.8	233.1
Operating and Maintenance	90.5	89.8	276.3	262.9
Depreciation	22.7	20.0	67.1	59.8
Total Operating Expenses	188.0	188.8	573.2	555.8
Operating Income (Loss)	38.9	35.3	115.8	113.1
Other Income (Expense) [Abstract]
Interest Expense	(10.9)	(9.7)	(32.6)	(28.1)
Equity Earnings in ATC	4.7	4.5	13.7	13.4
Other	0.5	0.6	2.3	3.8
Total Other Income (Expense)	(5.7)	(4.6)	(16.6)	(10.9)
Income (Loss) Before Non-Controlling Interest and Income Taxes	33.2	30.7	99.2	102.2
Income Tax Expense (Benefit)	12.7	11.2	24.7	40.5
Net Income (Loss)	20.5	19.5	74.5	61.7
Less: Non-Controlling Interest in Subsidiaries	0	(0.1)	(0.2)	(0.3)
Net Income (Loss) Attributable to ALLETE	$ 20.5	$ 19.6	$ 74.7	$ 62.0
Average Shares of Common Stock [Abstract]
Basic	35.6	34.4	35.1	34.1
Diluted	35.7	34.5	35.2	34.2
Basic Earnings Per Share of Common Stock	$ 0.57	$ 0.57	$ 2.13	$ 1.82
Diluted Earnings Per Share of Common Stock	$ 0.57	$ 0.56	$ 2.12	$ 1.81
Dividends Per Share of Common Stock	$ 0.445	$ 0.44	$ 1.335	$ 1.32