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Commitments, Guarantees and Contingencies - Air (Details) (Boswell Unit 4 [Member], USD $) In Millions, unless otherwise specified | Sep. 30, 2012
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Minimum [Member] |
Expected Capital Cost | $ 350.0
Maximum [Member] |
Expected Capital Cost | $ 400.0

X
- Definition Expected capital cost for each individual project. + References No definition available. + Details
Name: | ale_ExpectedCapitalCost
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant