XML 84 R70.htm IDEA: XBRL DOCUMENT
v3.10.0.1

Commitments, Guarantees and Contingencies - Legal Proceedings (Details) - U.S. Water Services [Member] - U.S. Water Services Patent Defense Litigation [Member] $ in Millions | 6 Months Ended
--- | ---
Jun. 30, 2018 USD ($)
Legal Proceedings [Line Items] |
Patents Infringed | 2
Addition to Intangible Assets for Patent Defense Costs | $ 2

X
- Definition Finite-Lived Intangible Assets Addition for Patent Defense Costs + References No definition available. + Details
Name: | ale_FiniteLivedIntangibleAssetsAdditionforPatentDefenseCosts
Namespace Prefix: | ale_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- 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_GainContingenciesLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of entity's patents that another entity has allegedly infringed. + References No definition available. + Details
Name: | us-gaap_GainContingencyPatentsAllegedlyInfringedUponNumber
Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | dei_LegalEntityAxis=ale_U.S.WaterServicesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_LitigationCaseAxis=ale_U.S.WaterServicesPatentDefenseLitigationMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |