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Investments | 12 Months Ended
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Dec. 31, 2018
Investments [Abstract] |
Investments [Text Block] | INVESTMENTS Investments. As of December 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 |  |
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.
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 in 2018, 2017 and 2016.

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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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