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Fair Value of FInancial Instruments Schedule of Fair Value (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | $ 65 us-gaap_MoneyMarketFundsAtCarryingValue | $ 59 us-gaap_MoneyMarketFundsAtCarryingValue
Domestic government, Debt securities | 14 us-gaap_USGovernmentSecuritiesAtCarryingValue | 14 us-gaap_USGovernmentSecuritiesAtCarryingValue
Corporate debt securities held in decommissioning trust assets | 11 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets | 9 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets
Domestic Equity Securities | 5 por_DomesticEquitySecurities | 7 por_DomesticEquitySecurities
International Equity Securities | 1 por_InternationalEquitySecurities | 1 por_InternationalEquitySecurities
Debt securities - domestic government |  | 1 por_DebtSecuritiesDomesticGovernment
Electricity | 5 por_CommodityContractAssetElectricity | 10 por_CommodityContractAssetElectricity
Natural gas | 2 por_CommodityContractAssetNaturalGas | 4 por_CommodityContractAssetNaturalGas
Financial Instruments, Owned, at Fair Value | 103 us-gaap_FinancialInstrumentsOwnedAtFairValue | 105 us-gaap_FinancialInstrumentsOwnedAtFairValue
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 112 por_CommodityContractLiabilitiesElectricity | 127 por_CommodityContractLiabilitiesElectricity
Natural gas | 116 por_CommodityContractLiabilitiesNaturalGas | 63 por_CommodityContractLiabilitiesNaturalGas
Liabilities, Fair Value Disclosure | 228 us-gaap_LiabilitiesFairValueDisclosure | 190 us-gaap_LiabilitiesFairValueDisclosure
Fair Value, Inputs, Level 1 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | 0 us-gaap_MoneyMarketFundsAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 us-gaap_MoneyMarketFundsAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Domestic government, Debt securities | 7 us-gaap_USGovernmentSecuritiesAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 6 us-gaap_USGovernmentSecuritiesAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Corporate debt securities held in decommissioning trust assets | 0 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Domestic Equity Securities | 4 por_DomesticEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 4 por_DomesticEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
International Equity Securities | 1 por_InternationalEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 1 por_InternationalEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Debt securities - domestic government |  | 1 por_DebtSecuritiesDomesticGovernment / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Electricity | 0 por_CommodityContractAssetElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 por_CommodityContractAssetElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Natural gas | 0 por_CommodityContractAssetNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 por_CommodityContractAssetNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Financial Instruments, Owned, at Fair Value | 12 us-gaap_FinancialInstrumentsOwnedAtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 12 us-gaap_FinancialInstrumentsOwnedAtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 0 por_CommodityContractLiabilitiesElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 por_CommodityContractLiabilitiesElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Natural gas | 0 por_CommodityContractLiabilitiesNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 por_CommodityContractLiabilitiesNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Liabilities, Fair Value Disclosure | 0 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member | 0 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member
Fair Value, Inputs, Level 2 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | 65 us-gaap_MoneyMarketFundsAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 59 us-gaap_MoneyMarketFundsAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Domestic government, Debt securities | 7 us-gaap_USGovernmentSecuritiesAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 8 us-gaap_USGovernmentSecuritiesAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Corporate debt securities held in decommissioning trust assets | 11 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 9 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Domestic Equity Securities | 1 por_DomesticEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 3 por_DomesticEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
International Equity Securities | 0 por_InternationalEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 0 por_InternationalEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Debt securities - domestic government |  | 0 por_DebtSecuritiesDomesticGovernment / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Electricity | 4 por_CommodityContractAssetElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 9 por_CommodityContractAssetElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Natural gas | 2 por_CommodityContractAssetNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 4 por_CommodityContractAssetNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Financial Instruments, Owned, at Fair Value | 90 us-gaap_FinancialInstrumentsOwnedAtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 92 us-gaap_FinancialInstrumentsOwnedAtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 32 por_CommodityContractLiabilitiesElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 10 por_CommodityContractLiabilitiesElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Natural gas | 95 por_CommodityContractLiabilitiesNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 40 por_CommodityContractLiabilitiesNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Liabilities, Fair Value Disclosure | 127 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | 50 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member
Fair Value, Inputs, Level 3 [Member] |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |
Money market funds | 0 us-gaap_MoneyMarketFundsAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0 us-gaap_MoneyMarketFundsAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Domestic government, Debt securities | 0 us-gaap_USGovernmentSecuritiesAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0 us-gaap_USGovernmentSecuritiesAtCarryingValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Corporate debt securities held in decommissioning trust assets | 0 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0 por_CorporateDebtSecuritiesHeldInDecommissioningTrustAssets / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Domestic Equity Securities | 0 por_DomesticEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0 por_DomesticEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
International Equity Securities | 0 por_InternationalEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0 por_InternationalEquitySecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Debt securities - domestic government |  | 0 por_DebtSecuritiesDomesticGovernment / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Electricity | 1 por_CommodityContractAssetElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 1 por_CommodityContractAssetElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Natural gas | 0 por_CommodityContractAssetNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 0 por_CommodityContractAssetNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Financial Instruments, Owned, at Fair Value | 1 us-gaap_FinancialInstrumentsOwnedAtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 1 us-gaap_FinancialInstrumentsOwnedAtFairValue / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Liabilities from price risk management activities: [Abstract] |  |
Electricity | 80 por_CommodityContractLiabilitiesElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 117 por_CommodityContractLiabilitiesElectricity / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Natural gas | 21 por_CommodityContractLiabilitiesNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 23 por_CommodityContractLiabilitiesNaturalGas / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Liabilities, Fair Value Disclosure | 101 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member | 140 us-gaap_LiabilitiesFairValueDisclosure / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member
Non Qualified Benefit Plans [Member] |  |
Liabilities from price risk management activities: [Abstract] |  |
Insurance contracts, at cash surrender value | $ 26 us-gaap_CashSurrenderValueFairValueDisclosure / por_TrustAxis = por_NonQualifiedBenefitPlansMember | $ 26 us-gaap_CashSurrenderValueFairValueDisclosure / por_TrustAxis = por_NonQualifiedBenefitPlansMember

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- Definition Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to purchases or sales of natural gas. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of electricity. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of natural gas. + References No definition available. + Details
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- Definition Corporate debt securities held in decommissioning trust assets + References No definition available. + Details
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- Definition debt securities - domestic government + References No definition available. + Details
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- Definition Fair value portion of the amount that could be realized under a life insurance contract or contracts owned by the entity, commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Surrender Value -URI http://asc.fasb.org/extlink&oid=6507153 + Details
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- Definition The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 940 -SubTopic 320 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969 + Details
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- Definition Fair value of financial and nonfinancial obligations. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 820 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258 + Details
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- Definition Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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- Definition Debt (bills, notes or bonds) that are issued by the government of the United States which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Cash Equivalents -URI http://asc.fasb.org/extlink&oid=6507016 + Details
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