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Jointly-owned Plant Schedule of Jointly-owned plant (Details) $ in Millions | Dec. 31, 2020 USD ($)
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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

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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 25 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=116646717&loc=d3e6290-110844 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 35 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7037-110846 + Details
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- Definition The period end amount owned by the reporting utility of a jointly owned utility plant in service. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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- Definition The period end amount of construction work in progress at a jointly owned electricity generation plant. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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- Definition The period end amount of accumulated depreciation in a jointly owned electricity generation plant. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 360 -Section S99 -Paragraph 1 -Subparagraph (SAB Topic 10.C) -URI http://asc.fasb.org/extlink&oid=115995737&loc=d3e659983-123033 + Details
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