Aggregate Lines of Credit, Available Borrowing Capacity (unused/outstanding)

No definition available.

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- Definition

Aggregate Lines of Credit, Total Borrowing Capacity

+ References

No definition available.

+ Details

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- Definition

Aggregate Lines of Credit, Used Borrowing Capacity

+ References

No definition available.

+ Details

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- Definition

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

+ References

No definition available.

+ Details

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- Definition

The balance sheet gross carrying amount of the specified debt instrument at period end.

+ References

No definition available.

+ Details

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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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- Details

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- Definition

This represents the allowed amount of letters of credit issuances under another credit agreement.

+ References

No definition available.

+ Details

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Period Type:	instant

- Definition

Line of Credit Borrowing Capacity Reduction

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
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Period Type:	instant

- 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.

+ Details

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- Definition

The stated principal amount of the debt instrument at time of issuance, which may vary from the carrying amount because of unamortized premium or discount.

+ References

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

-Publisher AICPA

-Name Accounting Principles Board Opinion (APB)

-Number 21

-Paragraph 16, 20

-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 FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=6584090&loc=d3e28878-108400

+ Details

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Period Type:	instant

- Definition

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

+ 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 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

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 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Details

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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

-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

Total of the portions of the carrying amounts as of the balance sheet date of long-term debt, which may include notes payable, bonds payable, debentures, mortgage loans, and commercial paper, which are scheduled to be repaid within one year 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 20

-Article 5

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-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 210.5-02.19,20)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- Definition

Amount of long-term debt maturities after year five following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 47

-Paragraph 10

-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.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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- Definition

Amount of long-term debt maturing in year five following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

+ Details

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- Definition

Amount of long-term debt maturing in year four following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

+ Details

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- Definition

Amount of long-term debt maturing in year three following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed of determinable prices and dates.

+ References

+ Details

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- Definition

Amount of long-term debt maturing in year two following the date of the latest balance sheet presented in the financial statements, which may include maturities of long-term debt, sinking fund requirements, and other securities redeemable at fixed or determinable prices and dates.

+ References

+ Details

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- Definition

Reflects the total carrying amount as of the balance sheet date of debt having initial terms less than 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(a))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 19

-Subparagraph a

-Article 5

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.(a),16(a)(1))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 13

-Article 9

-Subparagraph 2, 3

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 7

-Section 03

-Paragraph 16

-Subparagraph a(1)

+ Details

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Short-Term and Long-Term Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended						12 Months Ended		12 Months Ended
	Dec. 31, 2011	Aug. 25, 2011	Dec. 31, 2010	Feb. 01, 2012 Credit Agreement Feb 2012 [Member]	Dec. 31, 2011 Credit Agreement July 2011 [Member]	Jun. 30, 2011 Credit Agreement July 2011 [Member]	Dec. 31, 2011 Term Loan Agreement [Member]	Aug. 25, 2011 Term Loan Agreement [Member]	Dec. 31, 2011 ALLETE Properties LOC Nov 2011 [Member]	Nov. 14, 2011 ALLETE Properties LOC Nov 2011 [Member]	Sep. 30, 2011 ALLETE Properties LOC Nov 2011 [Member]	Oct. 07, 2011 ALLETE Properties LOC Oct 2011 [Member]
Financial Covenants [Abstract]
Debt Instrument, Required Indebtedness to Total Capital Ratio	0.65 to 1.00
Debt Instrument, Actual Indebtedness to Total Capital Ratio	0.44 to 1.00
Maturities of Long-term Debt [Abstract]
Long-term Debt, Current Maturities	$ 5.4		$ 13.4
Long-term Debt, Maturities, Repayments of Principal in Year Two	83.8
Long-term Debt, Maturities, Repayments of Principal in Year Three	94.1
Long-term Debt, Maturities, Repayments of Principal in Year Four	16.7
Long-term Debt, Maturities, Repayments of Principal in Year Five	21.0
Long-term Debt, Maturities, Repayments of Principal after Year Five	642.3
Debt Instrument [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				150.0	250.0	150.0				8.3	10.0	3.0
Line of Credit Borrowing Capacity Reduction									1.7
Letter of Credit Maximum Issuances				10.0	40.0
Debt Instrument, Face Amount		75.0						75.0
Debt Instrument, Description of Variable Rate Basis	one-month LIBOR						LIBOR
Debt Instrument, Basis Spread on Variable Rate	1.00%						1.00%
Debt Instrument, Interest Rate, Effective Percentage							1.825%
Debt Instrument, Carrying Amount at Period End							75.0
Short-term Debt [Abstract]
Short-term Debt	6.5		14.4
Aggregate Lines of Credit, Total Borrowing Capacity	256.4		154.0
Aggregate Lines of Credit, Used Borrowing Capacity	1.1		1.0
Aggregate Lines of Credit, Available Borrowing Capacity	$ 255.3		$ 153.0