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Earnings Per Share and Common Stock (Tables) | 9 Months Ended
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Sep. 30, 2021
Earnings Per Share [Abstract] |
Reconciliation of Basic and Diluted Earnings Per Share [Table Text Block] |
|  |  | 2021 |  |  |  |  |  | 2020 |  |
Reconciliation of Basic and Diluted |  |  | Dilutive |  |  |  |  |  | Dilutive |  |
Earnings Per Share | Basic |  | Securities |  | Diluted |  | Basic |  | Securities |  | Diluted
Millions Except Per Share Amounts |  |  |  |  |  |  |  |  |  |  |
Quarter ended September 30, |  |  |  |  |  |  |  |  |  |  |
Net Income Attributable to ALLETE | $27.6 |  |  |  |  | $27.6 |  |  | $40.7 |  |  |  |  | $40.7 |
Average Common Shares | 52.4 |  |  | 0.1 |  |  | 52.5 |  |  | 51.9 |  |  | 0.1 |  |  | 52.0 |
Earnings Per Share | $0.53 |  |  |  |  | $0.53 |  |  | $0.78 |  |  |  |  | $0.78 |
Nine Months Ended September 30, |  |  |  |  |  |  |  |  |  |  |
Net Income Attributable to ALLETE | $107.3 |  |  |  |  | $107.3 |  |  | $127.1 |  |  |  |  | $127.1 |
Average Common Shares | 52.3 |  |  | — |  |  | 52.3 |  |  | 51.8 |  |  | 0.1 |  |  | 51.9 |
Earnings Per Share | $2.05 |  |  |  |  | $2.05 |  |  | $2.45 |  |  |  |  | $2.45 |

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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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