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Investments (Tables)
 12 Months Ended
Dec. 31, 2018
Investments [Abstract]  
Other Investments [Table Text Block]
Other Investments
 
 
As of December 31
2018

2017

Millions
 
 
ALLETE Properties

$24.4


$26.4

Available-for-sale Securities (a)
20.2

19.1

Cash Equivalents
1.0

3.8

Other
3.5

3.8

Total Other Investments

$49.1


$53.1


(a)
As of December 31, 2018, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $2.0 million, in one year to less than three years was $2.9 million, in three years to less than five years was $2.6 million, and in five or more years was $0.5 million.