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Long-Term Debt - Additional Information (Details) - First Mortgage [Member]
$ in Millions
Dec. 31, 2024
USD ($)
Debt Instrument [Line Items]  
Debt Instrument, Interest Rate, Stated Percentage 8.00%
Avista Utilities [Member]  
Debt Instrument [Line Items]  
Amount of First Mortgage Bonds that Could be Issued, Percent 66.66%
Amount of First Mortgage Bonds that Could be Issued $ 1,500
Alaska Electric Light & Power [Member]  
Debt Instrument [Line Items]  
Amount of First Mortgage Bonds that Could be Issued, Percent 66.66%
Amount of First Mortgage Bonds that Could be Issued $ 56