Consolidated Statement of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net Income	$ 141.5	$ 125.5	$ 104.7
Other Comprehensive Income (Loss) [Abstract]
Unrealized Loss on Securities - Net of Income Taxes of $(0.3), $(0.2) and $–	(0.5)	(0.2)	0.0
Unrealized Gain on Derivatives - Net of Income Taxes of $0.1, $0.1 and $–	0.1	0.2	0.1
Defined Benefit Pension and Other Postretirement Benefit Plans - Net of Income Taxes of $(2.2), $(2.8) and $3.3	(3.0)	(4.0)	4.8
Total Other Comprehensive Income (Loss)	(3.4)	(4.0)	4.9
Total Comprehensive Income	138.1	121.5	109.6
Less: Non-Controlling Interest in Subsidiaries	0.4	0.7	0.0
Comprehensive Income Attributable to ALLETE	$ 137.7	$ 120.8	$ 109.6