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

No definition available.

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- Definition

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

+ References

No definition available.

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- Definition

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating 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)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Article 5

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- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

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- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

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- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

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-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

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-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

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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

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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.

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

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-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22)

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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.

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

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-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (b)

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Short-Term and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	3 Months Ended			0 Months Ended
	Apr. 02, 2013	Sep. 30, 2013	Dec. 31, 2012	Dec. 31, 2012 ALLETE Bonds 4.86% Series Due 2013 [Member]	Apr. 02, 2013 ALLETE Bonds 1.83% Due April 2018 [Member]	Apr. 02, 2013 ALLETE Bonds 3.30% Due October 2028 [Member]	Apr. 02, 2013 ALLETE Bonds 4.21% Due October 2043 [Member]	Aug. 26, 2013 ALLETE Amended Term Loan Variable Rate Due August 2015 [Member]	Aug. 26, 2013 ALLETE Amended Term Loan Variable Rate Due 2015 Effective August 26, 2013 [Member]	Aug. 26, 2013 ALLETE Amended Term Loan Variable Rate Due 2015 Effective August 26, 2014 [Member]
Financial Covenants [Abstract]
Required Indebtedness to Total Capital Ratio		0.65
Actual Indebtedness to Total Capital Ratio		0.46
Debt Instrument [Line Items]
Short-Term Debt Outstanding		$ 38.9	$ 84.5
Short-Term Debt Outstanding, Subsequently Matured		37.7	84.5	60.0
Long-Term Debt Outstanding		1,064.2	933.6
Proceeds from Issuance of First Mortgage Bonds	150.0				50.0	40.0	60.0
First Mortgage Bonds, Interest Rate					1.83%	3.30%	4.21%
Amended Term Loan, Principal Amount								$ 75.0
Amended Term Loan, Variable Rate Basis								one-month LIBOR
Amended Term Loan, Basis Spread on Variable Rate								0.875%
Amended Term Loan, Effective Interest Rate									1.70%	1.625%