Consolidated Statement of Comprehensive Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Comprehensive Income (Loss), Net of Tax, Attributable to Parent [Abstract]
Net Income	$ 125.5	$ 104.7	$ 97.1
Other Comprehensive Income (Loss) [Abstract]
Unrealized Gain (Loss) on Securities - Net of Income Taxes of $(0.2), $– and $0.8	(0.2)	0	1.2
Unrealized Gain (Loss) on Derivatives - Net of Income Taxes of $0.1, $– and $(0.1)	0.2	0.1	(0.2)
Defined Benefit Pension and Other Postretirement Benefit Plans - Net of Income Taxes of $(2.8), $3.3 and $3.9	(4.0)	4.8	5.9
Total Other Comprehensive Income (Loss)	(4.0)	4.9	6.9
Total Comprehensive Income	121.5	109.6	104.0
Less: Non-Controlling Interest in Subsidiaries	0.7	0	0
Comprehensive Income Attributable to ALLETE	$ 120.8	$ 109.6	$ 104.0