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Investments (Tables)
 6 Months Ended
Jun. 30, 2018
Investments [Abstract]  
Other Investments [Table Text Block]
Other Investments
June 30,
2018

 
December 31,
2017

Millions
 
 
 
ALLETE Properties

$25.9

 

$26.4

Available-for-sale Securities (a)
21.4

 
19.1

Cash Equivalents
1.5

 
3.8

Other
3.7

 
3.8

Total Other Investments

$52.5

 

$53.1


(a)
As of June 30, 2018, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $1.1 million, in one year to less than three years was $3.9 million, in three years to less than five years was $2.5 million and in five or more years was $1.1 million.