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REGULATORY MATTERS: Regulatory Matters Level 3 (Tables) | 12 Months Ended
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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 Return |  | Total as of December 31,
Description |  |  |  |  | 2025 |  | 2024
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) |  | 2026-2027 |  | 8,205 |  |  | (1,350) |  |  | 6,855 |  |  | 17,761 |
North Valmy plant settlements(6) |  | 2026-2033 |  | 83,941 |  |  | — |  |  | 83,941 |  |  | 80,767 |
Jim Bridger plant settlement(6) |  | 2026-2030 |  | 151,739 |  |  | 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 agreement |  | 2026-2043 |  | 11,313 |  |  | 7,326 |  |  | 18,639 |  |  | 19,796 |
Other |  | 2026-2056 |  | 4,596 |  |  | 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 costs |  |  |  | 16,493 |  |  | — |  |  | 16,493 |  |  | 9,277 |
Power supply costs(6) |  | 2026-2027 |  | 42,419 |  |  | — |  |  | 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 |
Other |  |  |  | 4,168 |  |  | 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 Year |  | Period Rates in Effect |  | Annual Amount (in millions of dollars)
2024 |  | June 1, 2025 to May 31, 2026 |  | $(3.1)
2023 |  | June 1, 2024 to May 31, 2025 |  | $36.8
2022 |  | June 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 Effect |  | OATT 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 |

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