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Short-Term and Long-Term Debt (Details) (USD $) In Millions | 6 Months Ended |  | 6 Months Ended |  |  |  |  |
--- | --- | --- | --- | --- | --- | --- | --- | ---
Jun. 30, 2011 | Dec. 31, 2010 | Jun. 30, 2011 Allete [Member] | May 25, 2011 Allete [Member] | Jan. 11, 2006 Allete [Member] | Jun. 30, 2011 Bni Coal [Member] | May 25, 2011 Bni Coal [Member] | Nov. 12, 2009 Bni Coal [Member]
Short-Term and Long-Term Debt (Details) [Abstract] |  |  |  |  |  |  |  |
Long-term debt outstanding | $ 770.7 | $ 771.6 |  |  |  |  |  |
Debt instrument, restrictive covenant | 0.65 to 1.00 |  |  |  |  |  |  |
Line of Credit Facility [Line Items] |  |  |  |  |  |  |  |
Credit Agreement |  |  |  | 250.0 | 150.0 |  | 10.0 | 3.0
Credit Agreement Effective Date |  |  | 07-01-2011 |  |  |  |  |
Credit Agreement Capacity Available for Issuance of Letters of Credit |  |  | 40.0 |  |  |  |  |
Credit Agreement Extension Available |  |  | 1Y |  |  |  |  |
Credit Agreement Expiration Date |  |  | 06-30-2015 |  |  |  |  |
Line of Credit Facility, Amount Withdrawn |  |  |  |  |  | 2.5 |  |
Debt instrument, actual restrictive covenant range (in hundredths) | 0.42 to 1.00 |  |  |  |  |  |  |
Debt due within one year | $ 15.4 | $ 14.4 |  |  |  |  |  |

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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 SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19 -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 210.5-02.19,20) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Description of minimum financial levels (for example, tangible net worth and working capital) and achievement of certain financial ratios (for example, working capital ratio and debt service coverage ratio), and adherence to certain clauses which generally require or restrict certain actions (for example, entering into a debt arrangement with equal or greater seniority, and selling or discontinuing a certain business segment or material subsidiary) to be in compliance with the covenant clauses of the debt agreement. May also include a discussion of the adverse consequences that would result if the entity violates or fails to satisfy the covenants. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 2, 4 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 22 -Article 5 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 470 -Section 50 -Paragraph 3 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823 + Details
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- Definition Amount borrowed under the credit facility as of the balance sheet date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 + Details
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- Definition Reflects when the credit facility terminates, which may be presented in a variety of ways (year, month and year, day, month and year, quarter). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Statement of Financial Accounting Standard (FAS) -Number 129 -Paragraph 2, 4 -LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy. Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 19, 22 -Article 5 Reference 3: 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(b),22(b)) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Definition Sum of the carrying values as of the balance sheet date of all long-term debt, which is debt initially having maturities due after one year from the balance sheet date or beyond the operating cycle, if longer, but excluding the portions thereof scheduled to be repaid within one year (current maturities) or the normal operating cycle, if longer, and after deducting unamortized discount or premiums, if any. + 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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