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Short-Term and Long-Term Debt (Tables) | 6 Months Ended
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Jun. 30, 2017
Debt Disclosure [Abstract] |
Schedule of Short-Term and Long-Term Debt [Table Text Block] | The following tables present ALLETE’s short-term and long-term debt as of June 30, 2017, and December 31, 2016:
June 30, 2017 | Principal |  |  | Unamortized Debt Issuance Costs |  | Total |
Millions |  |  |  |  |
Short-Term Debt |  | $118.2 |  |  | $(0.5) |  |  | $117.7 |
Long-Term Debt | 1,411.4 |  |  | (10.0) |  | 1,401.4 |
Total Debt |  | $1,529.6 |  |  | $(10.5) |  |  | $1,519.1 |
December 31, 2016 | Principal |  |  | Unamortized Debt Issuance Costs |  | Total |
Millions |  |  |  |  |
Short-Term Debt |  | $188.3 |  |  | $(0.6) |  |  | $187.7 |
Long-Term Debt | 1,380.8 |  |  | (10.4) |  | 1,370.4 |
Total Debt |  | $1,569.1 |  |  | $(11.0) |  |  | $1,558.1 |

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- Definition Tabular disclosure of information pertaining to short-term and long-debt instruments or arrangements, including but not limited to identification of terms, features, collateral requirements and other information necessary to a fair presentation. + References No definition available. + Details
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