XML 51 R35.htm IDEA: XBRL DOCUMENT
v3.19.1

Operations and Significant Accounting Policies - Sale of U.S. Water Services (Details) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 USD ($)
Sale of U.S. Water Services [Abstract] |
Cash Purchase Price | $ 270
Proceeds from Sale of U.S. Water Services - Net of Transaction Costs and Cash Retained | 265
Approximate Gain on Sale of U.S. Water Services, After-tax | $ 10

X
- Definition Approximate Gain on Sale of Affiliate, After-tax + References No definition available. + Details
Name: | ale_ApproximateGainonSaleofAffiliateAftertax
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Approximate Proceeds from Divestiture of Business + References No definition available. + Details
Name: | ale_ApproximateProceedsfromDivestitureofBusiness
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Cash Purchase Price for Sale of Affiliate + References No definition available. + Details
Name: | ale_CashPurchasePriceforSaleofAffiliate
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Sale of U.S. Water Services [Abstract] + References No definition available. + Details
Name: | ale_SaleofU.S.WaterServicesAbstract
Namespace Prefix: | ale_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration