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Investments | 3 Months Ended
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Mar. 31, 2018
Investments [Abstract] |
Investments [Text Block] | INVESTMENTS Investments. As of March 31, 2018, the investment portfolio included the legacy real estate assets of ALLETE Properties, debt and equity securities consisting primarily of securities held in other postretirement plans to fund employee benefits, the cash equivalents within these plans and other assets consisting primarily of land in Minnesota.
Other Investments | March 31, 2018 |  |  | December 31, 2017 |
Millions |  |  |
ALLETE Properties |  | $26.0 |  |  |  | $26.4 |
Available-for-sale Securities (a) | 21.1 |  |  | 19.1 |
Cash Equivalents | 2.0 |  |  | 3.8 |
Other | 3.7 |  |  | 3.8 |
Total Other Investments |  | $52.8 |  |  |  | $53.1 |
(a) | As of March 31, 2018, the aggregate amount of available-for-sale corporate and governmental debt securities maturing in one year or less was $0.9 million, in one year to less than three years was $3.4 million, in three years to less than five years was $3.3 million and in five or more years was $1.1 million.
Land Inventory. Land inventory is accounted for as held for use and is recorded at cost, unless the carrying value is determined not to be recoverable in accordance with the accounting standards for property, plant and equipment, in which case the land inventory is written down to estimated fair value. Land values are reviewed for indicators of impairment on a quarterly basis and no impairment was recorded for the three months ended March 31, 2018, and 2017. Available-for-Sale Securities. We account for our available-for-sale securities portfolio in accordance with the guidance for certain investments in debt and equity securities. Our available-for-sale securities portfolio consisted primarily of securities held in other postretirement plans to fund employee benefits. Gross realized and unrealized gains and losses on our available-for-sale securities were immaterial for the three months ended March 31, 2018, and 2017.

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- Definition The entire disclosure for investments, including all tables. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Article 6 -Section 10 -Paragraph (c) -Subparagraph (1) + Details
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- References No definition available. + Details
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