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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

Actual indebtedness to total capital ratio required to be maintained by most restrictive financial covenant.

+ References

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Indebtedness to total capital ratio required to be maintained by most restrictive financial covenant.

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- Definition

Short-Term Debt, Current Maturity First Mortgage Bonds 4.86%

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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



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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Article 5

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- Definition

Decrease for amounts repaid on the debt instrument for the period.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 235

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.4-08.(f))

-URI http://asc.fasb.org/extlink&oid=6881521&loc=d3e23780-122690



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- Definition

Interest rate stated in the contractual debt agreement.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

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- Definition

Amount borrowed under the credit facility as of the balance sheet date.

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-Name Regulation S-X (SX)

-Number 210

-Section 02

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- Definition

Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 129

-Paragraph 2, 4

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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.

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-Subparagraph (SX 210.5-02.22)

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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 Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 19

-Subparagraph b

-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.



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-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228



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-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

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-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.



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