The entity's adjusted requested amount of increase to existing rates, filed with the state regulatory commission.

Name:	ale_AdjustedRetailRateIncreaseRequest
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of estimated additional revenue generated on an annualized basis as a result of a rate increase.

+ Details

Name:	ale_AmountOfEstimatedAdditionalRevenue
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of differential between interim rates and final rates authorized for collection by the state regulatory commission through a rate case proceeding.

+ Details

Name:	ale_AmountOfRateDifferentialAuthorizedForCollection
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of revenue receivable capitalized, as part of rate base, as part of a stipulation and settlement agreement in a rate case.

+ Details

Name:	ale_AmountOfRevenueReceivableCapitalized
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of capital structure related to equity approved by the state regulatory commission through a rate case proceeding.

+ Details

Name:	ale_ApprovedPercentageOfCapitalStructureRelatedToEquity
Namespace Prefix:	ale
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Rate of return on common equity approved by the state regulatory commission through a rate case proceeding.

+ Details

Name:	ale_ApprovedRateOfReturnOnCommonEquity
Namespace Prefix:	ale
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The entity's approved amount of increase to electric rates, by the state regulatory commission.

+ Details

Name:	ale_ApprovedRetailRateIncrease
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The entity's approved rate of increase to existing rates, by the state regulatory commission.

+ Details

Name:	ale_ApprovedRetailRateIncreasePercent
Namespace Prefix:	ale
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The entity's interim rate increase to existing rates, as approved by the state regulatory commission.

+ Details

Name:	ale_InterimRateIncreaseImplemented
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

The length of notice required to terminate a contract in years.

+ Details

Name:	ale_LengthOfNoticeRequiredToTerminateYears
Namespace Prefix:	ale
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of municipalities that are non-affiliated municipal customers.

+ Details

Name:	ale_NonAffiliatedMunicipalCustomersMunicipalities
Namespace Prefix:	ale
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of private utilities that are non-affiliated municipal customers.

+ Details

Name:	ale_NonAffiliatedMunicipalCustomersPrivateUtilities
Namespace Prefix:	ale
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The entity's original requested amount of increase to existing rates, filed with the state regulatory commission.

+ Details

Name:	ale_OriginalRetailRateIncreaseRequest
Namespace Prefix:	ale
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of capital structure related to debt requested by utility through a rate case proceeding filed with the state regulatory commission.

+ Details

Name:	ale_RequestedPercentageOfCapitalStructureRelatedToDebt
Namespace Prefix:	ale
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of capital structure related to equity requested by utility through a rate case proceeding filed with the state regulatory commission.

+ Details

Name:	ale_RequestedPercentageOfCapitalStructureRelatedToEquity
Namespace Prefix:	ale
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Rate of return on common equity requested by utility through a rate case proceeding filed with the state regulatory commission.

+ Details

Name:	ale_RequestedRateOfReturnOnCommonEquity
Namespace Prefix:	ale
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_RegulatoryAssetsAndLiabilitiesOtherDisclosuresAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 71

-Paragraph 9, 10

-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 980

-SubTopic 340

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

+ Details

Name:	us-gaap_RegulatoryAssetsNoncurrent
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the effects of adjustments of previously recorded tax expense, significant settlements of income tax disputes, and unusual tax positions or infrequent actions taken by the entity, including tax assessment reversal, IRS tax settlement and unusual repatriation of foreign earnings.

+ References

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

-Publisher FASB

-Name FASB Interpretation (FIN)

-Number 48

-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 FASB Interpretation (FIN)

-Number 48

-Paragraph 10A, 10B, 10C

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 740

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319

+ Details

Name:	us-gaap_TaxAdjustmentsSettlementsAndUnusualProvisions
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Regulatory Matters (Details) (USD $) In Millions, unless otherwise specified															3 Months Ended
	Sep. 30, 2011	Dec. 31, 2010	May 24, 2011 2010 Rate Case [Member]	Mar. 31, 2011 2010 Rate Case [Member]	Dec. 31, 2010 2010 Rate Case [Member]	Nov. 02, 2010 2010 Rate Case [Member] Percent	Apr. 30, 2010 2010 Rate Case [Member] Percent	Nov. 02, 2009 2010 Rate Case [Member]	Sep. 30, 2011 FERC-Approved Wholesale Rates [Member]	Sep. 30, 2011 2010 Wisconsin Rate Increase [Member]	Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Percent	Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Water Rates [Member] Percent	Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Natural Gas Rates [Member] Percent	Dec. 31, 2010 2010 Wisconsin Rate Increase [Member] Electric Rates [Member] Percent	Mar. 31, 2011 DTL Reversal, Revenue Receivable Forgone [Member]	Jun. 30, 2011 Income Tax Benefit, MPUC Approval of Deferral of PPACA [Member]	Mar. 31, 2010 DTA Reversal, Elimination of Medicare Part D [Member]	Sep. 30, 2011 Medicare Part D [Member]	Dec. 31, 2010 Medicare Part D [Member]
Electric Rates [Abstract]
Original Retail Rate Increase Request								$ 81
Interim Rate Increase Implemented					48.5
Adjusted Retail Rate Increase Request							72
Requested Rate of Return on Common Equity							11.25%
Requested Percentage of Capital Structure Related to Equity							54.29%
Requested Percentage of Capital Structure Related to Debt							45.71%
Approved Retail Rate Increase			53.5			53.5
Approved Rate of Return on Common Equity						10.38%					10.90%
Approved Percentage of Capital Structure Related to Equity						54.29%
Amount of Rate Differential Authorized for Collection			3.2
Amount of Revenue Receivable Capitalized				20.5
Tax Adjustments, Settlements, and Unusual Provisions															6.2	2.9	4.0
Non-Affiliated Municipal Customers, Municipalities									16
Non-Affiliated Municipal Customers, Private Utilities									1
Length of Notice Required to Terminate (Years)									three
Amount Of Estimated Additional Revenue										2
Approved Retail Rate Increase (Percent)											2.40%	12.80%	2.50%	0.70%
The Patient Protection and Affordable Care Act of 2010 (PPACA) [Abstract]
Tax Adjustments, Settlements, and Unusual Provisions															6.2	2.9	4.0
Non-Current Regulatory Assets	$ 286.9	$ 310.2																$ 5.0	$ 0