Investments (Tables)

9 Months Ended

Sep. 30, 2015

Investments [Abstract]

Other Investments [Table Text Block]

Other Investments	September 30, 2015		December 31, 2014
Millions
ALLETE Properties		$88.3		$88.2
Available-for-sale Securities (a)	18.5		18.9
Cash Equivalents	2.6		2.9
Other	4.1		4.4
Total Other Investments		$113.5		$114.4

(a) As of September 30, 2015, the aggregate amount of available-for-sale corporate debt securities maturing in one year or less was $0.2 million, in one year to less than three years was $1.6 million, in three years to less than five years was $3.0 million, and in five or more years was $6.4 million.

Available-for-sale Securities [Table Text Block]

Available-For-Sale Securities
Millions		Gross Unrealized
	Cost	Gain	Loss	Fair Value
September 30, 2015	$20.1	$0.1	$1.7	$18.5
December 31, 2014	$19.6	$0.2	$0.9	$18.9
		Net	Gross Realized
		Proceeds	Gain	Loss
Quarter Ended September 30,
2015		—	—	—
2014		$0.6	—	—
Nine Months Ended September 30,
2015		$0.7	$0.1	—
2014		$3.3	$0.2	—