Acquisitions (Details)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Acquisitions [Abstract]
Business Combination, Reason for Business Combinations	The acquisitions below are consistent with ALLETE’s stated strategy of investing in energy infrastructure and related services businesses to complement its core regulated utility, balance exposure to business cycles and changing demand, and provide potential long-term earnings growth.
Business Acquisition, Pro Forma Information	not significant	not significant