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Earnings Per Share and Common Stock | 3 Months Ended
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Mar. 31, 2021
Earnings Per Share [Abstract] |
Earnings Per Share and Common Stock [Text Block] | EARNINGS PER SHARE AND COMMON STOCK We compute basic earnings per share using the weighted average number of shares of common stock outstanding during each period. The difference between basic and diluted earnings per share, if any, arises from non-vested restricted stock units and performance share awards granted under our Executive Long-Term Incentive Compensation Plan.
|  |  | 2021 |  |  |  |  |  | 2020 |  |
Reconciliation of Basic and Diluted |  |  | Dilutive |  |  |  |  |  | Dilutive |  |
Earnings Per Share | Basic |  | Securities |  | Diluted |  | Basic |  | Securities |  | Diluted
Millions Except Per Share Amounts |  |  |  |  |  |  |  |  |  |  |
Three Months Ended March 31, |  |  |  |  |  |  |  |  |  |  |
Net Income Attributable to ALLETE | $51.8 |  |  |  |  | $51.8 |  |  | $66.3 |  |  |  |  | $66.3 |
Average Common Shares | 52.1 |  |  | 0.1 |  |  | 52.2 |  |  | 51.7 |  |  | 0.1 |  |  | 51.8 |
Earnings Per Share | $0.99 |  |  |  |  | $0.99 |  |  | $1.28 |  |  |  |  | $1.28 |

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- Definition The entire disclosure for earnings per share. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=109243012&loc=SL65017193-207537 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -URI http://asc.fasb.org/topic&trid=2144383 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3630-109257 + Details
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