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Jointly Owned Electric Facilities | 12 Months Ended
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Dec. 31, 2024
Jointly Owned Utility Plant, Net Ownership Amount [Abstract] |
Jointly Owned Electric Facilities | NOTE 9. JOINTLY OWNED ELECTRIC FACILITIES The Company has a 15 percent ownership interest in Units 3 and 4 of Colstrip, and provides financing for its ownership interest in the project. In January 2023, the Company entered into an agreement to transfer its ownership in Colstrip Units 3 and 4 to Northwestern on December 31, 2025. The Company will retain responsibility for remediation obligations in existence at the time the transaction closes. See further discussion of the transaction within Note 22. Pursuant to the ownership and operating agreements among the co-owners, the Company’s share of related fuel costs as well as operating expenses for plant in service are included in the corresponding accounts in the Consolidated Statements of Income. The Company’s share of utility plant in service for Colstrip and accumulated depreciation (inclusive of the ARO assets and accumulated amortization) were as follows as of December 31 (dollars in millions):
|  | 2024 |  |  | 2023 |
Utility plant in service |  | $ | 401 |  |  | $ | 394 |
Accumulated depreciation |  |  | (355 | ) |  |  | (334 | )
See Note 11 for further discussion of AROs. While the obligations and liabilities with respect to Colstrip are to be shared among the co-owners on a pro-rata basis, many of the environmental liabilities are joint and several under the law, so that if any co-owner failed to pay its share of such liability, the other co-owners (or any one of them) could be required to pay the defaulting co-owner‘s share (or the entire liability).

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