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PROPERTY, PLANT AND EQUIPMENT AND JOINTLY-OWNED PROJECTS: Property, Plant and Equipmnt Level 4 (Details)
 12 Months Ended
Dec. 31, 2023
USD ($)
MWh
Dec. 31, 2022
USD ($)
Dec. 31, 2021
USD ($)
Public Utility, Property, Plant and Equipment      
Production $ 2,794,534,000 $ 2,700,494,000  
Transmission 1,392,338,000 1,346,463,000  
Distribution 2,454,458,000 2,192,135,000  
General and Other 650,202,000 589,375,000  
Utility plant in service 7,291,532,000 6,828,467,000  
Accumulated provision for depreciation (2,557,744,000) (2,465,279,000)  
Utility plant in service - net $ 4,733,788,000 $ 4,363,188,000  
Average depreciation rate 2.90% 2.70% 2.90%
Idaho Energy Resources Co. Coal purchases from Bridger Coal Company $ 275,405,000 $ 230,210,000 $ 180,550,000
Regulatory Liabilities $ 882,553,000 $ 860,601,000  
Jim Bridger Plant      
Public Utility, Property, Plant and Equipment      
Jointly Owned Utility Plant, Name Jim Bridger units 1-4    
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service $ 770,179,000    
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress 12,891,000    
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation $ 500,685,000    
Jointly Owned Utility Plant, Proportionate Ownership Share 33.00%    
Nameplate Capacity (in MW) | MWh [1] 775    
Valmy Plant      
Public Utility, Property, Plant and Equipment      
Jointly Owned Utility Plant, Name North Valmy unit 2(2)    
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service [2] $ 262,544,000    
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress [2] 2,237,000    
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation [2] $ 225,147,000    
Jointly Owned Utility Plant, Proportionate Ownership Share [2] 50.00%    
Nameplate Capacity (in MW) | MWh [1],[2] 145    
Production      
Public Utility, Property, Plant and Equipment      
Average depreciation rate 3.50% 2.89%  
Transmission      
Public Utility, Property, Plant and Equipment      
Average depreciation rate 1.90% 1.91%  
Distribution      
Public Utility, Property, Plant and Equipment      
Average depreciation rate 2.18% 2.15%  
General and Other      
Public Utility, Property, Plant and Equipment      
Average depreciation rate 5.21% 5.36%  
Bridger Coal Company      
Public Utility, Property, Plant and Equipment      
Idaho Energy Resources Co. Coal purchases from Bridger Coal Company $ 67,900,000 $ 60,400,000 59,700,000
Idaho Power Company      
Public Utility, Property, Plant and Equipment      
Utility plant in service 7,291,532,000 6,828,467,000  
Accumulated provision for depreciation (2,557,744,000) (2,465,279,000)  
Utility plant in service - net $ 4,733,788,000 $ 4,363,188,000  
Average depreciation rate 2.89% 2.66%  
Idaho Energy Resources Co. Coal purchases from Bridger Coal Company $ 275,405,000 $ 230,210,000 $ 180,550,000
Construction work in progress $ 985,500,000    
Ida-West Energy      
Public Utility, Property, Plant and Equipment      
Jointly Owned Utility Plant, Proportionate Ownership Share 50.00%    
Marysville Hydro Partners      
Public Utility, Property, Plant and Equipment      
Utility plant in service - net $ 14,900,000    
Hells Canyon Complex | Idaho Power Company      
Public Utility, Property, Plant and Equipment      
Construction work in progress 459,800,000    
IPUC authorized AFUDC Collection HCC Relicensing - Gross | Hells Canyon Complex | Idaho Power Company      
Public Utility, Property, Plant and Equipment      
Regulatory Liabilities 8,800,000    
IPUC authorized AFUDC Collection HCC Relicensing - Net | Hells Canyon Complex | Idaho Power Company      
Public Utility, Property, Plant and Equipment      
Regulatory Liabilities 6,500,000    
Deferred revenue-AFUDC      
Public Utility, Property, Plant and Equipment      
Regulatory Liabilities [3] $ 228,671,000 $ 207,528,000  
[1] Idaho Power’s share of nameplate capacity.
[2] Pursuant to an agreement with NV Energy, Idaho Power's participation in coal-fired operations of North Valmy ended in December 2019 at unit 1 and is planned to end no later than the end of 2025 at unit 2.
[3] Idaho Power is collecting revenue in the Idaho jurisdiction for AFUDC on HCC relicensing costs but is deferring revenue recognition of the amounts collected until the license is issued and the asset is placed in service under the new license.