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Short-Term and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified | 3 Months Ended | 9 Months Ended |  | 3 Months Ended |
--- | --- | --- | --- | --- | ---
Sep. 30, 2012 | Sep. 30, 2012 | Dec. 31, 2011 | Sep. 30, 2012 ALLETE First Mortgage Bonds 3.20% Due July2026 [Member] | Sep. 30, 2012 ALLETE First Mortgage Bonds 4.08% Due July2042 [Member] | Sep. 30, 2012 Industrial Development Revenue Bonds 6.5% Due 2025 [Member] | Jun. 30, 2012 ALLETE LOC Jan2014 [Member]
Short-Term and Long-Term Debt [Abstract] |  |  |  |  |  |  |
Short-Term Debt Outstanding | $ 67.6 | $ 67.6 | $ 6.5 |  |  |  |
Short-Term Debt, Current Maturity, First Mortgage Bonds 4.86% |  | 60 |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |
Long-Term Debt Outstanding | 947.6 | 947.6 | 857.9 |  |  |  |
Proceeds from Issuance of First Mortgage Bonds | 160.0 |  |  | 75.0 | 85.0 |  |
Interest Rate |  |  |  | 3.20% | 4.08% | 6.50% |
Amount of Redeemed Bonds |  |  |  |  |  | 6.0 |
Line of Credit, Amount Outstanding |  |  |  |  |  |  | 14.0
Line of Credit, Maximum Borrowing Capacity |  |  |  |  |  |  | $ 150.0
Required Indebtedness to Total Capital Ratio | 0.65 to 1.00 |  |  |  |  |  |
Actual Indebtedness to Total Capital Ratio | 0.46 to 1.00 | 0.46 to 1.00 |  |  |  |  |

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- Definition Short-Term Debt, Current Maturity First Mortgage Bonds 4.86% + References No definition available. + Details
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- Definition Carrying value as of the balance sheet date of the sum of short-term debt and current maturities of long-term debt and capital lease obligations, which are due within one year (or one business cycle if longer). + 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 210.5-02.19,20) -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 19 -Article 5 + Details
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