Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Comprehensive Income [Abstract]
Net Income	$ 46.4	$ 40.1
Other Comprehensive Income (Loss) [Abstract]
Unrealized Gain (Loss) on Securities Net of Income Taxes of $(0.3), and $0.1	(0.4)	0.1
Unrealized Gain on Derivatives Net of Income Taxes of $– and $–	0.0	0.1
Defined Benefit Pension and Other Postretirement Benefit Plans Net of Income Taxes of $0.1 and $0.2	0.2	0.3
Total Other Comprehensive Income (Loss)	(0.2)	0.5
Total Comprehensive Income	46.2	40.6
Less: Non-Controlling Interest in Subsidiaries	0.5	0.2
Comprehensive Income Attributable to ALLETE	$ 45.7	$ 40.4