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Common Stock and Earnings Per Share (Tables) | 12 Months Ended
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Dec. 31, 2021
Equity [Abstract] |
Summary of Common Stock [Table Text Block] |
Summary of Common Stock | Shares | Equity
| Thousands | Millions
Balance as of December 31, 2018 | 51,509 |  | $1,428.5 |
Employee Stock Purchase Plan | 8 |  | 0.7 |
Invest Direct | 38 |  | 3.0 |
Options and Stock Awards | 85 |  | 1.3 |
Contributions to RSOP | 39 |  | 3.2 |
Balance as of December 31, 2019 | 51,679 |  | 1,436.7 |
Employee Stock Purchase Plan | 13 |  | 0.7 |
Invest Direct | 309 |  | 18.3 |
Options and Stock Awards | 35 |  | 2.2 |
Contributions to RSOP | 49 |  | 3.0 |
Balance as of December 31, 2020 | 52,085 |  | 1,460.9 |
Employee Stock Purchase Plan | 17 |  | 0.8 |
Invest Direct | 263 |  | 17.5 |
Options and Stock Awards | 49 |  | 3.4 |
Contributions to RSOP | 24 |  | 3.1 |
Equity Issuance Program | 782 |  | 51.0 |
Balance as of December 31, 2021 | 53,220 |  | $1,536.7 |
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 |  |  |
2021 |  |  |
Net Income Attributable to ALLETE | $169.2 |  |  | $169.2 |
Average Common Shares | 52.4 |  | 0.1 |  | 52.5 |
Earnings Per Share | $3.23 |  |  | $3.23 |
2020 |  |  |
Net Income Attributable to ALLETE | $174.2 |  |  | $174.2 |
Average Common Shares | 51.9 |  | — |  | 51.9 |
Earnings Per Share | $3.36 |  |  | $3.35 |
2019 |  |  |
Net Income Attributable to ALLETE | $185.6 |  |  | $185.6 |
Average Common Shares | 51.6 |  | 0.1 |  | 51.7 |
Earnings Per Share | $3.59 |  |  | $3.59 |

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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/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=124432515&loc=d3e3550-109257 + Details
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