Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Comprehensive Income [Abstract]
Net Income	$ 60.3	$ 41.6	$ 122.7	$ 92.3
Other Comprehensive Income [Abstract]
Unrealized Gain (Loss) on Securities, Net of Income Taxes of $(0.4), $–, $(0.3) and $0.1	(0.7)	(0.1)	(0.6)	0.1
Unrealized Gain on Derivatives, Net of Income Taxes of $–, $–, $0.1 and $0.1	0.0	0.1	0.1	0.1
Defined Benefit Pension and Other Postretirement Benefit Plans, Net of Income Taxes of $0.3, $0.2, $0.7 and $0.6	0.3	0.2	1.0	0.8
Total Other Comprehensive Income (Loss)	(0.4)	0.2	0.5	1.0
Total Comprehensive Income	59.9	41.8	123.2	93.3
Less: Non-Controlling Interest in Subsidiaries	(0.1)	0.0	(0.1)	0.4
Comprehensive Income Attributable to ALLETE	$ 60.0	$ 41.8	$ 123.3	$ 92.9