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Summary Of Significant Accounting Policies Summary of Significant Accounting Policies (Details) $ in Millions | Sep. 30, 2019 USD ($)
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AFUDC above FERC allowed rate (1) |
Regulatory Assets [Line Items] |
Reclassification of Prior Year Amounts to Comply with Regulatory Requirements | $ 37

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- Definition Reclassification of Prior Year Amounts to Comply with Regulatory Requirements + References No definition available. + Details
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Namespace Prefix: | ava_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- Details
Name: | us-gaap_RegulatoryAssetAxis=ava_AFUDCAboveFERCAllowedRateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |