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REGULATORY MATTERS: Regulatory Matters Level 3 (Tables)
 12 Months Ended
Dec. 31, 2025
Regulatory Assets and Liabilities, Other Disclosure [Abstract]  
Schedule of Regulatory Assets and Liabilities
The following table presents a summary of Idaho Power’s regulatory assets and liabilities (in thousands of dollars):
As of December 31, 2025
Remaining
Amortization Period
Earning a Return(1)
Not Earning a ReturnTotal as of December 31,
Description20252024
Regulatory Assets:    
Income taxes(2)
 $— $821,346 $821,346 $811,054 
Pension expense deferrals(3)
245,508 1,832 247,340 252,197 
Mark-to-market assets(4)
— 49,520 49,520 28,118 
Unfunded postretirement benefits(5)
— — — 18,824 
Power supply costs(6)
— — — 18,507 
Fixed cost adjustment(6)
2026-20278,205 (1,350)6,855 17,761 
North Valmy plant settlements(6)
2026-203383,941 — 83,941 80,767 
Jim Bridger plant settlement(6)
2026-2030151,739 12,921 164,660 147,451 
Wildfire Mitigation Plan deferral(6)
— 91,670 91,670 63,966 
Asset retirement obligations(7)
 — 62,166 62,166 37,842 
Long-term service agreement2026-204311,313 7,326 18,639 19,796 
Other2026-20564,596 13,725 18,321 11,089 
Total $505,302 $1,059,156 $1,564,458 $1,507,372 
Regulatory Liabilities:     
Income taxes(8)
 $— $121,489 $121,489 $127,634 
Depreciation-related excess deferred income taxes(9)
128,180 — 128,180 137,903 
Removal costs(7)
 — 162,652 162,652 166,181 
Investment tax credits — 235,724 235,724 230,322 
Deferred revenue-AFUDC(10)
 224,083 56,896 280,979 250,942 
Energy efficiency program costs16,493 — 16,493 9,277 
Power supply costs(6)
2026-202742,419 — 42,419 3,949 
Unfunded postretirement benefits(5)
 — 11,785 11,785 — 
Tax reform accrual for future amortization(11)
— 44,423 44,423 42,266 
Other4,168 3,839 8,007 15,852 
Total $415,343 $636,808 $1,052,151 $984,326 
(1) Earning a return includes either interest or a return on the investment as a component of rate base at the allowed rate of return. The interest rate on deferral accounts is published annually by the IPUC and OPUC. The applicable rates for 2025 were 5.0% and 4.5%, respectively.
(2) Represents flow-through income tax accounting differences which have a corresponding deferred tax liability disclosed in Note 2 - "Income Taxes."
(3) Idaho Power records a regulatory asset for the difference between net periodic pension cost and pension cost considered for rate-making purposes relating to Idaho Power's defined benefit pension plan. In its Idaho jurisdiction, Idaho Power’s inclusion of pension costs for the establishment of retail rates is based upon contributions made to the pension plan. This regulatory asset account represents the difference between cumulative cash contributions and amounts collected in rates. Deferred costs are amortized into expense as the amounts are provided for in Idaho retail revenues.
(4) This item is discussed in more detail in Note 16 - "Derivative Financial Instruments."
(5) Represents the unfunded obligation of Idaho Power’s pension and postretirement benefit plans, which are discussed in Note 12 - "Benefit Plans."
(6) This item is discussed in more detail in this Note 3 - "Regulatory Matters."
(7) Asset retirement obligations and removal costs are discussed in Note 14 - "Asset Retirement Obligations (ARO)."
(8) Represents the tax gross-up related to the depreciation-related excess deferred income taxes and investment tax credits included in this table and has a corresponding deferred tax asset disclosed in Note 2 - "Income Taxes."
(9) For depreciation-related temporary differences under the normalized tax accounting method, the resulting excess deferred taxes will flow back to customers ratably over the remaining regulatory lives of Idaho Power's plant assets under the alternative method provided in the statute.
(10) 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.
(11) Represents amount accrued under the May 2018 Idaho tax reform settlement stipulation (described below) for the future amortization of existing or future unspecified regulatory deferrals that would otherwise be a future liability recoverable from Idaho customers.
Schedule of Power Cost Adjustment Changes
The table below summarizes the three most recent Idaho-jurisdiction PCA rate adjustments from Idaho Power's annual PCA filings, which also include non-PCA-related rate adjustments as ordered by the IPUC:
Effective Date$ Change (millions)Notes
June 1, 2025$(94.8)The $94.8 million net decrease in PCA rates reflects a decrease in the balancing adjustment, which is due primarily to the completed recovery of the 2023 balancing adjustment, which was recovered over two years.
June 1, 2024$(35.7)The $35.7 million net decrease in PCA rates reflected forecasted improved hydropower generation during the April 2024 to March 2025 PCA deferral period.
June 1, 2023$105.1 The $105.1 million increase in PCA rates reflected higher market energy and natural gas prices, combined with lower than-expected low-cost hydropower generation and limited coal supply. The increased rate also reflected an expectation of continued elevated market energy prices and natural gas prices in the forecast period.
Schedule of Fixed Cost Rate Adjustments
The following table summarizes FCA amounts approved for (refund) or collection in the prior three FCA years:
FCA YearPeriod Rates in EffectAnnual Amount
 (in millions of dollars)
2024June 1, 2025 to May 31, 2026$(3.1)
2023June 1, 2024 to May 31, 2025$36.8
2022June 1, 2023 to May 31, 2024$25.1
Schedule of Open Access Transmission Rates Idaho Power's OATT rates submitted to the FERC in Idaho Power's four most recent annual OATT Final Informational Filings were as follows:
Period Rates in EffectOATT Rate (per kW-year)
October 1, 2025 to September 30, 2026$34.16 
October 1, 2024 to September 30, 2025$31.55 
October 1, 2023 to September 30, 2024$30.74 
October 1, 2022 to September 30, 2023$31.42