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Jointly-owned Plant Schedule of Jointly-owned plant (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2017 USD ($)
Jointly Owned Utility Plant Interests [Line Items] |
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman | 90.00%
Jointly Owned Plant, Boardman Plant In Service Year | 1980
Jointly Owned Utility Plant, Gross Ownership Amount of Boardman Plant In Service | $ 515
Jointly Owned Utility Plant, Ownership Amount of Boardman Plant Accumulated Depreciation | 426
Jointly Owned Utility Plant Ownership Amount of Construction Work In Progress Boardman | $ 0
Jointly Owned Utility Plant, Proportionate Ownership Share of Colstrip | 20.00%
Jointly Owned Plant, Colstrip Plant In Service Year | 1986
Jointly Owned Utility Plant, Gross Ownership Amount of Colstrip Plant In Service | $ 546
Jointly Owned Utility Plant, Ownership Amount of Colstrip Plant Accumulated Depreciation | 351
Jointly Owned Utility Plant Ownership Amount Of Construction Work In Progress Colstrip | $ 5
Jointly Owned Utility Plant, Proportionate Ownership Share of Pelton/Round Butte | 66.67%
Jointly Owned Plant, Pelton Plant in Service Year | 1958
Jointly Owned Plant, Round Butte in Service Year | 1964
Jointly Owned Utility Plant, Gross Ownership Amount of Pelton/Round Butte Plant In Service | $ 251
Jointly Owned Utility Plant, Ownership Amount of Pelton/Round Butte Plant Accumulated Depreciation | 68
Jointly Owned Utility Plant Ownership Amount Of Construction Work In Progress Pelton/Round Butte | 7
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service | 1,312
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation | 845
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress | $ 12

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- Definition Jointly Owned Plant, Colstrip Plant In Service Year + References No definition available. + Details
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- Definition Jointly Owned Plant, Pelton in Service Year + References No definition available. + Details
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- Definition Jointly Owned Plant, Round Butte in Service Year + References No definition available. + Details
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X
- Definition The period end amount owned by the reporting entity of a jointly owned utility (Boardman) plant in service. + References No definition available. + Details
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X
- Definition The period end amount owned by the reporting entity of a jointly owned utility (Colstrip) plant in service. + References No definition available. + Details
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X
- Definition The period end amount owned by the reporting entity of utility plant (Pelton/Round Butte) plant in service. + References No definition available. + Details
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Balance Type: | debit
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X
- Definition The period end amount owned by the reporting entity of a jointly owned electricity generating facility (Boardman) plant accumulated depreciation. + References No definition available. + Details
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- Definition The period end amount owned by the reporting entity of a jointly owned electricity generating facility (Colstrip) plant accumulated depreciation. + References No definition available. + Details
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X
- Definition The reporting entity's period end amount of construction work in progress at Boardman, a jointly owned electricity generation plant. + References No definition available. + Details
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- Definition The reporting entity's period end amount of construction work in progress at Colstrip, a jointly owned electricity generation plant. + References No definition available. + Details
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- Definition The reporting entity's period end amount of construction work in progress at Pelton/Round Butte, a jointly owned electricity generation plant. + References No definition available. + Details
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- Definition The period end amount owned by the reporting entity of a jointly owned electricity generating facility (Pelton/Round Butte) plant accumulated depreciation. + References No definition available. + Details
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- Definition The proportionate share of the reporting entity's interest (percent) in Boardman, a jointly owned utility plant. + References No definition available. + Details
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- Definition The proportionate share of the reporting entity's interest (percent) in Colstrip, a jointly owned utility plant. + References No definition available. + Details
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X
- Definition The reporting entity's interest (percent) in Pelton/Round/Butte, a jointly owned utility plant. + References No definition available. + 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://www.xbrl.org/2003/role/presentationRef -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=6500719&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://www.xbrl.org/2003/role/presentationRef -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=6500719&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://www.xbrl.org/2003/role/presentationRef -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=6500719&loc=d3e659983-123033 + Details
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