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Jointly-owned Plant Jointly Owned Plant (Details) (USD $) | 1 Months Ended | 3 Months Ended | 12 Months Ended |  |
--- | --- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Sep. 30, 2013 | Dec. 31, 1985
Property, Plant and Equipment [Line Items] |  |  |  |  |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman transferred | 10.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareofBoardmantransferred | 10.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareofBoardmantransferred | 10.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareofBoardmantransferred | 15.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareofBoardmantransferred |  |  | 15.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareofBoardmantransferred
Property, Plant and Equipment, Additions | $ 7,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEquipment | $ 7,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEquipment | $ 7,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedEquipment |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory | 4,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory | 4,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory | 4,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedInventory |  |  |  |
Asset Retirement Obligation, Liabilities Incurred | 7,000,000 us-gaap_AssetRetirementObligationLiabilitiesIncurred | 8,000,000 us-gaap_AssetRetirementObligationLiabilitiesIncurred | 15,000,000 us-gaap_AssetRetirementObligationLiabilitiesIncurred | 4,000,000 us-gaap_AssetRetirementObligationLiabilitiesIncurred | 0 us-gaap_AssetRetirementObligationLiabilitiesIncurred |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities | 6,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities | 6,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities | 6,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedCurrentLiabilities |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities | 4,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities | 4,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities | 4,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedNoncurrentLiabilities |  |  |  |
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities | 2,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities | 2,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities | 2,000,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedFinancialLiabilities |  |  |  |
Asset Retirement Obligation Increase related to Boardman plant |  |  |  | 7,000,000 por_AssetRetirementObligationIncreaseRelatedToBoardmanPlant |  |  |
Interest in Pacific Northwest Intertie |  |  |  |  |  |  | 10.714%por_InterestinPacificNorthwestIntertie
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds | $ 8,000,000 us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds | $ 8,000,000 us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds | $ 8,000,000 us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds | $ 1 us-gaap_SignificantAcquisitionsAndDisposalsAcquisitionCostsOrSaleProceeds |  |  |
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman | 90.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareOfBoardman | 90.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareOfBoardman | 90.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareOfBoardman | 80.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareOfBoardman |  | 65.00%por_JointlyOwnedUtilityPlantProportionateOwnershipShareOfBoardman |

X
- Definition Asset Retirement Obligation Increase related to Boardman plant due to updated decommissioning study. + References No definition available. + Details
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- Definition Interest in Pacific Northwest Intertie + 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 Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman transferred + References No definition available. + Details
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- Definition Amount of asset retirement obligations incurred during the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -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 + Details
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- Definition Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Definition Amount of tangible personal property used to produce goods and services, including, but is not limited to, tools, dies and molds, computer and office equipment, acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Definition The amount of financial liabilities assumed (as defined) which have been recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Financial Liability -URI http://asc.fasb.org/extlink&oid=6513127 + Details
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- Definition The amount of inventory recognized as of the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 55 -Paragraph 37 -URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464 + Details
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- Definition Amount of liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472 + Details
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- Details
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- Definition The value of all consideration given or received by the Entity in the significant acquisition or disposal. + References No definition available. + Details
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