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Earnings Per Share and Common Stock (Details) (USD $) In Millions, except Per Share data, unless otherwise specified | 0 Months Ended | 3 Months Ended | 6 Months Ended
--- | --- | --- | ---
Mar. 04, 2014 | Feb. 26, 2014 | Jun. 30, 2014 | Jun. 30, 2013 | Jun. 30, 2014 | Jun. 30, 2013
Earnings Per Share and Common Stock [Abstract] |  |  |  |  |  |
Antidilutive Shares Excluded from Diluted EPS Computation |  |  | 0 | 0 | 0 | 0
Earnings Per Share - Basic [Abstract] |  |  |  |  |  |
Net Income Attributable to ALLETE |  |  | $ 16.8 | $ 14.0 | $ 50.3 | $ 46.5
Average Common Shares |  |  | 42.1 | 39.4 | 41.7 | 39.2
Earnings Per Share |  |  | $ 0.40 | $ 0.36 | $ 1.21 | $ 1.19
Earnings Per Share - Diluted [Abstract] |  |  |  |  |  |
Net Income to Attributable ALLETE |  |  | 16.8 | 14.0 | 50.3 | 46.5
Average Common Shares |  |  | 42.3 | 39.6 | 41.9 | 39.3
Earnings Per Share |  |  | $ 0.40 | $ 0.35 | $ 1.20 | $ 1.18
Dilutive Securities (in shares) |  |  | 0.2 | 0.2 | 0.2 | 0.1
Forward Contract Indexed to Issuer's Equity, Indexed Shares |  | 2.8 |  |  |  |
Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share |  | $ 48.01 |  |  |  |
Common Stock Issued - Option Agreement (in shares) | 0.4 |  |  |  |  |
Proceeds from Issuance of Common Stock - Option Agreement | 20.2 |  |  |  |  |
Forward Contract Indexed to Issuer's Equity, Dilutive Securities (in shares) |  |  |  |  | 0 |
Forward Contract Indexed to Issuer's Equity, Initial Fair Value |  | 0 |  |  |  |
Common Stock Issued - Pension Plan (in shares) |  |  |  |  | 0.4 |
Proceeds from Issuance of Common Stock - Pension Plan |  |  |  |  | $ 19.5 | $ 0

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- Definition Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Antidilution -URI http://asc.fasb.org/extlink&oid=6505113 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Diluted Earnings Per Share -URI http://asc.fasb.org/extlink&oid=6510752 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Contingent Stock Agreement -URI http://asc.fasb.org/extlink&oid=6508534 + Details
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- Definition Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.29) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 30 -Article 5 + Details
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