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Investments (Tables) | 6 Months Ended
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Jun. 30, 2016
Investments [Abstract] |
Other Investments [Table Text Block] |
Other Investments | June 30, 2016 |  |  | December 31, 2015 |
Millions |  |  |
ALLETE Properties |  | $47.8 |  |  |  | $50.1 |
Available-for-sale Securities (a) | 18.4 |  |  | 18.5 |
Cash Equivalents | 2.3 |  |  | 2.0 |
Other | 3.8 |  |  | 4.0 |
Total Other Investments |  | $72.3 |  |  |  | $74.6 |
(a) | As of June 30, 2016, 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 $2.5 million, in three years to less than five years was $5.0 million, and in five or more years was $3.3 million.

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