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Investments (Tables) | 9 Months Ended
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Sep. 30, 2017
Investments [Abstract] |
Other Investments [Table Text Block] |
Other Investments | September 30, 2017 |  |  | December 31, 2016 |
Millions |  |  |
ALLETE Properties |  | $28.8 |  |  |  | $31.7 |
Available-for-sale Securities (a) | 21.0 |  |  | 18.8 |
Cash Equivalents | 2.2 |  |  | 1.3 |
Other | 3.8 |  |  | 3.8 |
Total Other Investments |  | $55.8 |  |  |  | $55.6 |
(a) | As of September 30, 2017, 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 $3.2 million, in three years to less than five years was $4.2 million and in five or more years was $1.6 million.

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