Capital cost spent to date for project.

No definition available.

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Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
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- Definition

Civil Penalty

+ References

No definition available.

+ Details

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Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Definition

The estimated amount of certain future capital expenditures related to environmental compliance, regulatory matters, or other committments and/or contingencies.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

The estimated amount of certain capital expenditures related to environmental compliance, regulatory matters, or other commitments and/or contingencies. This estimate includes expenditures expected in future periods and expenditures made through the end of the current period.

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

- Definition

Estimated Environmental Compliance Costs

+ References

No definition available.

+ Details

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Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

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Data Type:	num:powerItemType
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- Definition

The charge against earnings in the period for known or estimated future costs arising from requirements to perform environmental remediation activities.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 30

-Section 50

-Paragraph 12

-URI http://asc.fasb.org/extlink&oid=6393242&loc=d3e13296-110859

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Details

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- Details

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- Details

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Commitments, Guarantees and Contingencies - Environmental Matters (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2014 MW
Clean Water Act - Aquatic Organisms [Member]
Environmental Matters [Line Items]
Estimated Environmental Compliance Costs		$ 15
Coal Combustion Residuals [Member]
Environmental Matters [Line Items]
Estimated Environmental Compliance Costs		130
Boswell Unit 4 [Member]
Environmental Matters [Line Items]
Estimated Capital Expenditures		250
Capital Cost Spent to Date		145
NOV Consent Decree Obligation [Member]
Environmental Matters [Line Items]
Generating Capacity (MW)		200.0
Environmental Remediation Expense		4.2
Civil Penalty	1.4
NOV Consent Decree [Member]
Environmental Matters [Line Items]
Generating Capacity (MW)		500.0
Estimated Capital Expenditures		600
NOV Consent Decree [Member] \| Minimum [Member]
Environmental Matters [Line Items]
Estimated Capital Expenditures		20
NOV Consent Decree [Member] \| Maximum [Member]
Environmental Matters [Line Items]
Estimated Capital Expenditures		$ 40