- Definition

The annual percentage change of the capacity charge specified in a power purchase, power sales, or electric sales agreement.

+ References

No definition available.

+ Details

Name:	ale_ChangeinAnnualCapacityChargePerContractPercentage
Namespace Prefix:	ale_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Capacity of a generating facility, unit, or project in megawatts.

+ References

No definition available.

+ Details

Name:	ale_GeneratingCapacityMw
Namespace Prefix:	ale_
Data Type:	num:powerItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	ale_LengthOfNoticeRequiredToTerminateYears
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Customers

+ References

No definition available.

+ Details

Name:	ale_NumberOfCustomers
Namespace Prefix:	ale_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of public utility's approved equity to capital, including debt and equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedEquityCapitalStructurePercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of public utility's approved return on equity.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_PublicUtilitiesGeneralDisclosuresLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	ale_CustomerClassAxis=ale_MunicipalCustomersMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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- Details

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Regulatory Matters - Utility Rates (Details)	Jan. 01, 2013	Jun. 01, 2011	Sep. 30, 2015 Customers Years MW
Bison Wind Energy Center [Member]
Public Utilities, General Disclosures [Line Items]
Generating Capacity (MW) \| MW			497
MPUC 2010 Minnesota Rate Case [Member] \| Electric Rates [Member] \| Retail Customers [Member]
Public Utilities, General Disclosures [Line Items]
Approved Rate of Return on Common Equity		10.38%
Approved Percentage of Capital Structure Related to Equity		54.29%
MPUC 2010 Minnesota Rate Case [Member] \| Electric Rates [Member] \| Municipal Customers [Member]
Public Utilities, General Disclosures [Line Items]
Approved Rate of Return on Common Equity		10.38%
FERC-Approved Wholesale Rates [Member] \| Electric Rates [Member] \| Municipal Customers [Member]
Public Utilities, General Disclosures [Line Items]
Number of Customers			16
Length of Notice Required to Terminate (Years) \| Years			3
FERC-Approved Wholesale Rates [Member] \| Electric Rates [Member] \| Municipal Customers [Member] \| Wholesale Electric Contracts (Expire December 2024) [Member]
Public Utilities, General Disclosures [Line Items]
Number of Customers			14
FERC-Approved Wholesale Rates [Member] \| Electric Rates [Member] \| Municipal Customers [Member] \| Minimum [Member] \| Wholesale Electric Contracts (Expire December 2024) [Member]
Public Utilities, General Disclosures [Line Items]
Annual Change in Capacity Charge, Percent			(1.00%)
FERC-Approved Wholesale Rates [Member] \| Electric Rates [Member] \| Municipal Customers [Member] \| Maximum [Member] \| Wholesale Electric Contracts (Expire December 2024) [Member]
Public Utilities, General Disclosures [Line Items]
Annual Change in Capacity Charge, Percent			2.00%
PSCW 2012 Wisconsin Rate Case [Member] \| Retail Customers [Member]
Public Utilities, General Disclosures [Line Items]
Approved Rate of Return on Common Equity	10.90%