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Summary of Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Property, Plant and Equipment [Line Items]      
Other Investments $ 120us-gaap_OtherInvestments $ 104us-gaap_OtherInvestments  
Business days after the invoice date 16    
Days after the due date 45    
Wholesale accounts receivable written off 0por_Wholesaleaccountsreceivablewrittenoff 0por_Wholesaleaccountsreceivablewrittenoff 0por_Wholesaleaccountsreceivablewrittenoff
Margin deposit 11us-gaap_MarginDepositAssets 9us-gaap_MarginDepositAssets  
Letters of Credit Outstanding, Amount 30us-gaap_LettersOfCreditOutstandingAmount 29us-gaap_LettersOfCreditOutstandingAmount  
Expenses related to Cascade Crossing 0por_ExpensesrelatedtoCascadeCrossing 52por_ExpensesrelatedtoCascadeCrossing 0por_ExpensesrelatedtoCascadeCrossing
Public Utilities, Allowance for Funds Used During Construction, Rate 7.40%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate 7.50%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate 7.50%us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionRate
Public Utilities, Allowance for Funds Used During Construction, Capitalized Interest 22us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest 7us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest 4us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest
Allowance for equity funds used during construction 37us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity 13us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity 6us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity
Depreciation expense rate 3.60%por_DepreciationExpenseRate 3.70%por_DepreciationExpenseRate 3.80%por_DepreciationExpenseRate
Asset Retirement Removal Costs Included in Depreciation Expense 57por_AssetRetirementRemovalCostsIncludedInDepreciationExpense 55por_AssetRetirementRemovalCostsIncludedInDepreciationExpense 55por_AssetRetirementRemovalCostsIncludedInDepreciationExpense
Finite-Lived Intangible Assets, Accumulated Amortization 191us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization 170us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization  
Amortization of Intangible Assets 25us-gaap_AmortizationOfIntangibleAssets 22us-gaap_AmortizationOfIntangibleAssets 22us-gaap_AmortizationOfIntangibleAssets
Future Amortization Expense, Year One 35us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths    
Future Amortization Expense, Year Two 33us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo    
Future Amortization Expense, Year Three 29us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree    
Future Amortization Expense, Year Four 28us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour    
Future Amortization Expense, Year Five 22us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive    
Power Cost Deadband - Lower Threshold 15por_PowerCostDeadbandLowerThreshold    
Power Cost Deadband - Upper Threshold 30por_PowerCostDeadbandUpperThreshold    
Public Utilities, Approved Return on Equity, Percentage 9.75%us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage 10.00%us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage 10.00%us-gaap_PublicUtilitiesApprovedReturnOnEquityPercentage
Net Variable Power Cost Underrun (7)por_NetVariablePowerCostUnderrun   (17)por_NetVariablePowerCostUnderrun
Net variable power cost overrun   11por_Netvariablepowercostoverrun  
Estimated Refund Under Power Cost Adjustment Mechanism 0por_EstimatedRefundUnderPowerCostAdjustmentMechanism 0por_EstimatedRefundUnderPowerCostAdjustmentMechanism 0por_EstimatedRefundUnderPowerCostAdjustmentMechanism
Actual Refund Under Power Cost Adjustment Mechanism   0por_ActualRefundUnderPowerCostAdjustmentMechanism 0por_ActualRefundUnderPowerCostAdjustmentMechanism
Franchise taxes 42por_FranchiseTaxes 41por_FranchiseTaxes 42por_FranchiseTaxes
Deferred Tax Assets, Regulatory Assets and Liabilities 48us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities 33us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities  
Noncurrent Regulatory Assets [Member]      
Property, Plant and Equipment [Line Items]      
Deferred Tax Assets, Regulatory Assets and Liabilities 86us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities
/ us-gaap_RegulatoryAssetAxis
= por_NoncurrentRegulatoryAssetsMember		 76us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities
/ us-gaap_RegulatoryAssetAxis
= por_NoncurrentRegulatoryAssetsMember		  
Noncurrent Regulatory Liabilities [Member]      
Property, Plant and Equipment [Line Items]      
Asset Retirement Obligations, Noncurrent $ 39us-gaap_AssetRetirementObligationsNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= por_NoncurrentRegulatoryLiabilitiesMember		 $ 39us-gaap_AssetRetirementObligationsNoncurrent
/ us-gaap_RegulatoryLiabilityAxis
= por_NoncurrentRegulatoryLiabilitiesMember