Long-Term Debt to Affiliated Trusts - Additional Information (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2026	Dec. 31, 2000
Debt Instrument [Line Items]
Payments for repurchase of trust preferred securities		$ 10
1997 Floating Rate Junior Subordinated Deferrable Interest Debentures, Series B [Member] \| Avista Capital II [Member]
Debt Instrument [Line Items]
Junior subordinated debenture issuance date	1997
Principal amount	$ 52
Avista Corp [Member]
Debt Instrument [Line Items]
Noncontrolling interest, ownership percentage by parent	100.00%
Trust Preferred Securities Subject to Mandatory Redemption [Member] \| 1997 Floating Rate Junior Subordinated Deferrable Interest Debentures, Series B [Member] \| Avista Capital II [Member]
Debt Instrument [Line Items]
Principal amount	$ 50
Debt instrument, basis spread on variable rate	1.137%
Debt Instrument, Variable Interest Rate, Type [Extensible Enumeration]	Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate [Member]
Common Trust Securities [Member] \| 1997 Floating Rate Junior Subordinated Deferrable Interest Debentures, Series B [Member] \| Avista Capital II [Member]
Debt Instrument [Line Items]
Principal amount	$ 2

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