Jointly-owned Plant Schedule of Jointly-owned plant (Details) $ in Millions	Dec. 31, 2023 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	$ 788
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	528
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	19
Colstrip [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	572
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	456
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	1
Pelton/Round Butte Member
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	216
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	72
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 18

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 980
-SubTopic 360
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.C)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479960/980-360-S99-1

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

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- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

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- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

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