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Commitments, Guarantees and Contingencies - Hydro Operations (Details) (Hydro Project [Member], USD $) In Millions, unless otherwise specified	Jun. 30, 2014
Hydro Project [Member]
Hydro Operations [Line Items]
Estimated Capital Expenditures, Including Past Expenditures	$ 90
Capital Cost Spent to Date	$ 75.5

X

- Definition

Capital cost spent to date for project.

+ References

No definition available.

+ Details

Name:	ale_CapitalCostSpentToDate
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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- 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

Name:	ale_EstimatedCapitalExpendituresIncludingPastExpenditures
Namespace Prefix:	ale_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Details

Name:	ale_HydroOperationsLineItems
Namespace Prefix:	ale_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration