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REGULATORY MATTERS: Idaho Fixed Cost Adjustment (Details) - USD ($)
$ in Millions
 12 Months Ended
May 31, 2024
Jun. 01, 2023
Jun. 01, 2022
Jun. 01, 2021
Idaho Fixed Cost Adjustment [Line Items]        
Annual fixed cost adjustment mechanism deferral   $ 25.1 $ 35.2 $ 38.3
Idaho Fixed Cost Adjustment [Member]        
Idaho Fixed Cost Adjustment [Line Items]        
Percentage cap on the FCA adjustment   3.00%    
Idaho Jurisdiction Fixed Cost Adjustment        
Idaho Fixed Cost Adjustment [Line Items]        
Annual fixed cost adjustment mechanism deferral   $ 25.1 $ 35.2  
Idaho Jurisdiction Fixed Cost Adjustment | Subsequent Event        
Idaho Fixed Cost Adjustment [Line Items]        
Public Utilities, Requested Rate Increase (Decrease), Amount $ 10.1