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Common Stock and Earnings Per Share (Tables) | 12 Months Ended
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Dec. 31, 2014
Common Stock and Earnings Per Share [Abstract] |
Summary of Common Stock [Table Text Block] |
Summary of Common Stock | Shares |  | Equity |
| Thousands |  | Millions |
Balance as of December 31, 2011 | 37,513 |  |  | $705.6 |
Employee Stock Purchase Program | 20 |  | 0.8 |
Invest Direct | 474 |  | 19.2 |
Options and Stock Awards | 95 |  | 6.0 |
Equity Issuance Program | 1,275 |  | 53.1 |
Balance as of December 31, 2012 | 39,377 |  | 784.7 |
Employee Stock Purchase Program | 16 |  | 0.7 |
Invest Direct | 395 |  | 18.5 |
Options and Stock Awards | 301 |  | 17.9 |
Equity Issuance Program | 1,312 |  | 63.4 |
Balance as of December 31, 2013 | 41,401 |  | 885.2 |
Employee Stock Purchase Program | 18 |  | 0.8 |
Invest Direct | 378 |  | 18.9 |
Options and Stock Awards | 78 |  | 8.0 |
Equity Issuance Program | 1,851 |  | 90.0 |
Forward Sale Agreement and Issuance | 1,807 |  | 85.2 |
Contributions to Pension | 396 |  | 19.5 |
Balance as of December 31, 2014 | 45,929 |  |  | $1,107.6 |
Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block] |
Reconciliation of Basic and Diluted |  |  |
Earnings Per Share |  |  | Dilutive |  |  |
Year Ended December 31 | Basic |  | Securities |  | Diluted |
Millions Except Per Share Amounts |  |  |
2014 |  |  |
Net Income Attributable to ALLETE |  | $124.8 |  |  |  |  | $124.8 |
Average Common Shares | 42.9 |  | 0.2 |  | 43.1 |
Earnings Per Share |  | $2.91 |  |  |  |  | $2.90 |
2013 |  |  |
Net Income Attributable to ALLETE |  | $104.7 |  |  |  |  | $104.7 |
Average Common Shares | 39.7 |  | 0.1 |  | 39.8 |
Earnings Per Share |  | $2.64 |  |  |  |  | $2.63 |
2012 |  |  |
Net Income Attributable to ALLETE |  | $97.1 |  |  |  |  | $97.1 |
Average Common Shares | 37.6 |  | — |  | 37.6 |
Earnings Per Share |  | $2.59 |  |  |  |  | $2.58 |

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- Definition Tabular disclosure of the change in common stock outstanding. + References No definition available. + Details
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- Definition Tabular disclosure of an entity's basic and diluted earnings per share calculations, including a reconciliation of numerators and denominators of the basic and diluted per-share computations for income from continuing operations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 + Details
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