Consolidated Statement of Income (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Consolidated Statement of Income [Abstract]
Operating Revenue	$ 216.4	$ 219.9	$ 456.4	$ 462.1
Operating Expenses [Abstract]
Fuel and Purchased Power	72.1	76.0	149.2	155.0
Operating and Maintenance	96.2	95.7	196.1	185.8
Depreciation	24.8	22.1	49.4	44.4
Total Operating Expenses	193.1	193.8	394.7	385.2
Operating Income	23.3	26.1	61.7	76.9
Other Income (Expense) [Abstract]
Interest Expense	(10.1)	(11.0)	(21.1)	(21.7)
Equity Earnings in ATC	4.8	4.6	9.4	9.0
Other	1.2	1.0	1.9	1.8
Total Other Expense	(4.1)	(5.4)	(9.8)	(10.9)
Income Before Non-Controlling Interest and Income Taxes	19.2	20.7	51.9	66.0
Income Tax Expense	4.8	3.8	13.1	12.0
Net Income	14.4	16.9	38.8	54.0
Less: Non-Controlling Interest in Subsidiaries	0	(0.1)	0	(0.2)
Net Income Attributable to ALLETE	$ 14.4	$ 17.0	$ 38.8	$ 54.2
Average Shares of Common Stock [Abstract]
Basic	37.3	35.0	37.0	34.8
Diluted	37.4	35.1	37.1	34.9
Basic Earnings Per Share of Common Stock	$ 0.39	$ 0.49	$ 1.05	$ 1.56
Diluted Earnings Per Share of Common Stock	$ 0.39	$ 0.48	$ 1.05	$ 1.55
Dividends Per Share of Common Stock	$ 0.46	$ 0.445	$ 0.92	$ 0.89