Jointly-owned Plant Schedule of Jointly-owned plant (Details) $ in Millions	Dec. 31, 2020 USD ($)
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	$ 849
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	469
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	14
Accrued Capping, Closure, Post-closure and Environmental Costs, Noncurrent	44
Colstrip [Member]
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	566
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	387
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	7
Pelton/Round Butte Member
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	283
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	82
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 7

The estimated amount of costs required as of the balance sheet date to comply with regulatory requirements pertaining to the retirement of a waste management facility, which will be paid after one year or beyond the normal operating cycle, if longer.

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- Definition

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

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

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

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