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REGULATORY MATTERS: Regulatory Assets and Liabilities Table (Details) - USD ($) $ in Thousands | Dec. 31, 2023 | Dec. 31, 2022
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Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets |  | $ 1,653,050 | $ 1,501,961
Regulatory Liabilities |  | 882,553 | 860,601
Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1] | 630,899 |
Regulatory Liabilities | [1] | 336,964 |
Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets |  | 1,022,151 |
Regulatory Liabilities |  | 545,589 |
Income taxes |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [2] | 108,641 | 94,946
Income taxes | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[2] | 0 |
Income taxes | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [2] | 108,641 |
Depreciation-related excess deferred income taxes |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [3] | 147,950 | 158,634
Depreciation-related excess deferred income taxes | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[3] | 147,950 |
Depreciation-related excess deferred income taxes | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [3] | 0 |
Removal costs |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [4] | 175,369 | 180,087
Removal costs | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[4] | 0 |
Removal costs | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [4] | 175,369 |
Investment tax credits |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 165,479 | 115,285
Investment tax credits | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1] | 0 |
Investment tax credits | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 165,479 |
Deferred revenue-AFUDC |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [5] | 228,671 | 207,528
Deferred revenue-AFUDC | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[5] | 177,884 |
Deferred revenue-AFUDC | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [5] | 50,787 |
Energy efficiency regulatory liability |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [6] | 1,507 | 154
Energy efficiency regulatory liability | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[6] | 1,507 |
Energy efficiency regulatory liability | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [6] | 0 |
Power supply costs |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [7] | 1,240 | 0
Power supply costs | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[7] | 1,240 |
Power supply costs | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [7] | 0 |
Mark to Market liabilities |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 88 | 59,544
Mark to Market liabilities | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1] | 0 |
Mark to Market liabilities | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 88 |
Tax reform accrual for future amortization |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [8] | 40,891 | 32,793
Tax reform accrual for future amortization | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1],[8] | 0 |
Tax reform accrual for future amortization | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [8] | 40,891 |
Other regulatory assets (liabilities) |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 12,717 | 11,630
Other regulatory assets (liabilities) | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities | [1] | 8,383 |
Other regulatory assets (liabilities) | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Liabilities |  | 4,334 |
Income taxes |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [9] | 774,672 | 739,689
Income taxes | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[9] | 0 |
Income taxes | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [9] | 774,672 |
Unfunded postretirement benefits |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [10] | 87,318 | 70,254
Unfunded postretirement benefits | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[10] | 0 |
Unfunded postretirement benefits | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [10] | 87,318 |
Pension expense deferrals |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [11] | 255,244 | 249,503
Pension expense deferrals | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[11] | 253,744 |
Pension expense deferrals | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [11] | 1,500 |
Energy efficiency regulatory asset |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [6] | 0 | 3,767
Energy efficiency regulatory asset | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[6] | 0 |
Energy efficiency regulatory asset | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [6] | 0 |
Power supply costs |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 115,525 | 129,309
Power supply costs | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[7] | 134,816 |
Power supply costs | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 19,291 |
Fixed cost adjustment |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 51,285 | 41,901
Fixed cost adjustment | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[7] | 36,037 |
Fixed cost adjustment | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 15,248 |
Valmy Plant settlements |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 82,917 | 90,747
Valmy Plant settlements | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[7] | 82,917 |
Valmy Plant settlements | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 0 |
Jim Bridger Plant |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 123,632 | 80,531
Jim Bridger Plant | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[7] | 108,376 |
Jim Bridger Plant | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 15,256 |
Wildfire Mitigation Plan Deferral |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 51,329 | 27,078
Wildfire Mitigation Plan Deferral | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[7] | 0 |
Wildfire Mitigation Plan Deferral | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [7] | 51,329 |
Asset retirement obligation |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [4] | 35,270 | 28,780
Asset retirement obligation | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1],[4] | 0 |
Asset retirement obligation | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [4] | 35,270 |
Long-term service agreement |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets |  | 20,955 | 22,114
Long-term service agreement | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1] | 12,679 |
Long-term service agreement | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets |  | 8,276 |
Other regulatory assets (liabilities) |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets |  | 54,903 | $ 18,288
Other regulatory assets (liabilities) | Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets | [1] | 2,330 |
Other regulatory assets (liabilities) | Not Earning a Return |  |  |
Regulatory Assets and Liabilities [Line Items] |  |  |
Regulatory Assets |  | $ 52,573 |
[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 2023 were 2% and 4.5%, respectively.
[2] | 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."
[3] | In 2017, income tax reform reduced deferred income tax assets and liabilities. 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.
[4] | Asset retirement obligations and removal costs are discussed in Note 13 - "Asset Retirement Obligations (ARO)."
[5] | 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.
[6] | The energy efficiency asset and liability represent the separate Idaho and Oregon jurisdiction balances at December 31, 2022, and December 31, 2023, respectively. During 2023, the balances changed from an asset to a liability in the Idaho jurisdiction.
[7] | This item is discussed in more detail in this Note 3 - "Regulatory Matters."
[8] | 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.
[9] | Represents flow-through income tax accounting differences which have a corresponding deferred tax liability disclosed in Note 2 - "Income Taxes."
[10] | Represents the unfunded obligation of Idaho Power’s pension and postretirement benefit plans, which are discussed in Note 11 - "Benefit Plans."
[11] | 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.

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