Comprehensive Income (Details) (USD $) In Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Comprehensive Income (Loss)
Net Income	$ 16.9	$ 19.4	$ 54.0	$ 42.2
Other Comprehensive Income
Unrealized Gain on Securities Net of Income Taxes	0.2	(0.6)	1.1	(0.5)
Defined Benefit Pension and Other Postretirement Plans Net of Income Taxes	0.4	0.3	0.8	0.6
Total Other Comprehensive Income	0.6	(0.3)	1.9	0.1
Total Comprehensive Income	17.5	19.1	55.9	42.3
Less: Non-Controlling Interest in Subsidiaries	(0.1)	0	(0.2)	(0.2)
Comprehensive Income Attributable to ALLETE	17.6	19.1	56.1	42.5
Income Taxes on Unrealized Gains on Securities	0.2	(0.4)	0.8	(0.4)
Income Taxes on Defined Benefit Pension and Other Postretirement Plans	$ 0.2	$ 0.2	$ 0.5	$ 0.4