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Balance Sheet Components - Schedule of Regulatory Assets and Liabilities (Parenthetical) (Details) $ in Millions | 9 Months Ended
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Sep. 30, 2021 USD ($)
Regulated Asset Liability [Line Items] |
Change to flow-through tax treatment of certain basis adjustments | $ 128.8

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- Definition Increase decrease in flow-through tax treatment of certain basis adjustments. + References No definition available. + Details
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Namespace Prefix: | ava_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Regulated Asset Liability [Line Items] + References No definition available. + Details
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Namespace Prefix: | ava_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration