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Short-Term and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified | 0 Months Ended | 3 Months Ended |
--- | --- | --- | ---
Apr. 02, 2013 | Jun. 30, 2013 | Dec. 31, 2012
Financial Covenants [Abstract] |  |  |
Required Indebtedness to Total Capital Ratio |  | 0.65 |
Actual Indebtedness to Total Capital Ratio |  | 0.47 |
Debt Instrument [Line Items] |  |  |
Short-Term Debt Outstanding |  | $ 37.9 | $ 84.5
Long-Term Debt Outstanding |  | 1,064.7 | 933.6
Proceeds from Issuance of First Mortgage Bonds | 150.0 |  |
ALLETE Bonds 4.86% Series Due 2013 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Short-Term Debt Outstanding |  |  | 60.0
ALLETE Bonds 1.83% Due April 2018 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Proceeds from Issuance of First Mortgage Bonds | 50.0 |  |
First Mortgage Bonds, Interest Rate | 1.83% |  |
ALLETE Bonds 3.30% Due October 2028 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Proceeds from Issuance of First Mortgage Bonds | 40.0 |  |
First Mortgage Bonds, Interest Rate | 3.30% |  |
ALLETE Bonds 4.21% Due October 2043 [Member] |  |  |
Debt Instrument [Line Items] |  |  |
Proceeds from Issuance of First Mortgage Bonds | $ 60.0 |  |
First Mortgage Bonds, Interest Rate | 4.21% |  |

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- Definition Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant. + References No definition available. + Details
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- Definition Contractual interest rate for funds borrowed, under the debt agreement. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22(a)(1)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Amount of long-term debt, after unamortized discount or premium, scheduled to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + 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 20 -Article 5 Reference 3: 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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- Definition Carrying amount of long-term debt, net of unamortized discount or premium, excluding amounts to be repaid within one year or the normal operating cycle, if longer (current maturities). Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.22) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition The cash inflow from amounts received from a long-term debt instrument secured by a first mortgage deed of trust, containing a pledge of real property. The lender has the highest claim on the property in case of default. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financing Activities -URI http://asc.fasb.org/extlink&oid=6513228 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585 + Details
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