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BENEFIT PLANS: Schedule Defined Benefit Plans Disclosures (Details) - USD ($)
 12 Months Ended
Dec. 31, 2023
Dec. 31, 2022
Dec. 31, 2021
Change in Fair Value of Plan Assets [Roll Forward]      
Employer contributions $ 9,800,000 $ 8,800,000 $ 8,200,000
Noncurrent liabilities (233,965,000) (238,037,000)  
Less amount recorded as regulatory assets 1,653,050,000 1,501,961,000  
Pension Plan      
Change in Benefit Obligation [Roll Forward]      
Benefit obligation at January 1 953,769,000 1,346,530,000  
Service cost 29,843,000 52,025,000 54,202,000
Interest cost 51,277,000 39,670,000 37,317,000
Actuarial (gain) loss 41,539,000 (438,297,000)  
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment 0 0  
Benefits Paid 48,412,000 46,159,000  
Projected benefit obligation at December 31 1,028,016,000 953,769,000 1,346,530,000
Change in Fair Value of Plan Assets [Roll Forward]      
Fair value at January 1 839,728,000 984,464,000  
Actual return (loss) on plan assets 78,197,000 (138,577,000)  
Employer contributions 48,000,000 40,000,000  
Benefits Paid (48,412,000) (46,159,000)  
Fair value at December 31 917,513,000 839,728,000 984,464,000
Funded status at end of year (110,503,000) (114,041,000)  
Other current liabilities 0 0  
Noncurrent liabilities (110,503,000) (114,041,000)  
Net amount recognized (110,503,000) (114,041,000)  
Net loss 108,334,000 83,263,000  
Prior service cost 31,000 37,000  
Subtotal 108,365,000 83,300,000  
Less amount recorded as regulatory assets [1] 108,365,000 83,300,000  
Net amount recognized in accumulated other comprehensive income 0 0  
Accumulated benefit obligation 892,325,000 837,377,000  
Senior Management Security Plan      
Change in Benefit Obligation [Roll Forward]      
Benefit obligation at January 1 99,976,000 133,012,000  
Service cost 612,000 1,185,000 813,000
Interest cost 5,322,000 3,897,000 3,557,000
Actuarial (gain) loss 6,518,000 (32,009,000)  
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment 11,000 0  
Benefits Paid 6,630,000 6,109,000  
Projected benefit obligation at December 31 105,809,000 99,976,000 133,012,000
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 (105,809,000) (99,976,000)  
Other current liabilities (6,608,000) (6,514,000)  
Noncurrent liabilities (99,201,000) (93,462,000)  
Net amount recognized (105,809,000) (99,976,000)  
Net loss 21,074,000 15,127,000  
Prior service cost 2,200,000 2,408,000  
Subtotal 23,274,000 17,535,000  
Less amount recorded as regulatory assets 0 0  
Net amount recognized in accumulated other comprehensive income 23,274,000 17,535,000  
Accumulated benefit obligation $ 99,786,000 $ 93,995,000  
[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.