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BENEFIT PLANS: Schedule Defined Benefit Plans Disclosures (Details) - USD ($)
 12 Months Ended
Dec. 31, 2025
Dec. 31, 2024
Dec. 31, 2023
Change in Fair Value of Plan Assets [Roll Forward]      
Employer contributions $ 10,900,000 $ 10,400,000 $ 9,800,000
Noncurrent liabilities (137,406,000) (165,992,000)  
Less amount recorded as regulatory assets 1,564,458,000 1,507,372,000  
Pension Plan      
Change in Benefit Obligation [Roll Forward]      
Benefit obligation at January 1 998,166,000 1,028,016,000  
Service cost 31,774,000 33,992,000 29,843,000
Interest cost 56,151,000 52,181,000 51,277,000
Actuarial (gain) loss 5,237,000 (65,972,000)  
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment 0 0  
Benefits Paid 52,309,000 50,051,000  
Projected benefit obligation at December 31 1,039,019,000 998,166,000 1,028,016,000
Change in Fair Value of Plan Assets [Roll Forward]      
Fair value at January 1 951,142,000 917,513,000  
Actual return (loss) on plan assets 104,542,000 63,680,000  
Employer contributions 20,000,000 20,000,000  
Benefits Paid (52,309,000) (50,051,000)  
Fair value at December 31 1,023,375,000 951,142,000 917,513,000
Funded status at end of year (15,644,000) (47,024,000)  
Other current liabilities 0 0  
Noncurrent liabilities (15,644,000) (47,024,000)  
Net amount recognized (15,644,000) (47,024,000)  
Net loss 13,142,000 43,516,000  
Prior service cost 18,000 24,000  
Subtotal 13,160,000 43,540,000  
Less amount recorded as regulatory assets [1] 13,160,000 43,540,000  
Net amount recognized in accumulated other comprehensive income 0 0  
Accumulated benefit obligation 895,190,000 863,705,000  
Senior Management Security Plan      
Change in Benefit Obligation [Roll Forward]      
Benefit obligation at January 1 102,318,000 105,809,000  
Service cost 1,172,000 1,051,000 612,000
Interest cost 5,640,000 5,332,000 5,322,000
Actuarial (gain) loss 2,401,000 (3,321,000)  
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment 7,000 15,000  
Benefits Paid 6,900,000 6,568,000  
Projected benefit obligation at December 31 104,638,000 102,318,000 105,809,000
Change in Fair Value of Plan Assets [Roll Forward]      
Fair value at January 1 0 0  
Actual return (loss) on plan assets 0 0  
Employer contributions 0 0  
Benefits Paid 0 0  
Fair value at December 31 0 0 $ 0
Funded status at end of year (104,638,000) (102,318,000)  
Other current liabilities (6,855,000) (6,827,000)  
Noncurrent liabilities (97,783,000) (95,491,000)  
Net amount recognized (104,638,000) (102,318,000)  
Net loss 18,154,000 16,442,000  
Prior service cost 1,780,000 1,995,000  
Subtotal 19,934,000 18,437,000  
Less amount recorded as regulatory assets 0 0  
Net amount recognized in accumulated other comprehensive income 19,934,000 18,437,000  
Accumulated benefit obligation $ 99,105,000 $ 96,487,000  
[1] Changes in the funded status of the pension plan that would be recorded in AOCI for an unregulated entity are recorded as a regulatory asset for Idaho Power as Idaho Power believes it is probable that an amount equal to the regulatory asset will be collected through the setting of future rates.