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Common Stock and Earnings Per Share (Tables) | 12 Months Ended
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Dec. 31, 2012
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, 2009 | 35,221 |  |  | $613.4 |
Employee Stock Purchase Program | 19 |  | 0.6 |
Invest Direct | 346 |  | 11.7 |
Options and Stock Awards | 51 |  | 4.4 |
Equity Issuance Program | 180 |  | 6.0 |
Balance as of December 31, 2010 | 35,817 |  |  | $636.1 |
Employee Stock Purchase Program | 20 |  | 0.8 |
Invest Direct | 437 |  | 17.2 |
Options and Stock Awards | 109 |  | 6.7 |
Equity Issuance Program | 400 |  | 16.0 |
Purchase of Non-Controlling Interest | 222 |  | 8.8 |
Contributions to Pension | 508 |  | 20.0 |
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 |
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 |  |  |
2012 |  |  |
Net Income Attributable to ALLETE |  | $97.1 |  |  |  |  | $97.1 |
Average Common Shares | 37.6 |  | — |  | 37.6 |
Earnings Per Share |  | $2.59 |  |  |  |  | $2.58 |
2011 |  |  |
Net Income Attributable to ALLETE |  | $93.8 |  |  |  |  | $93.8 |
Average Common Shares | 35.3 |  | 0.1 |  | 35.4 |
Earnings Per Share |  | $2.66 |  |  |  |  | $2.65 |
2010 |  |  |
Net Income Attributable to ALLETE |  | $75.3 |  |  |  |  | $75.3 |
Average Common Shares | 34.2 |  | 0.1 |  | 34.3 |
Earnings Per Share |  | $2.20 |  |  |  |  | $2.19 |

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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. + References No definition available. + Details
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