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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 | $ 120 us-gaap_OtherInvestments | $ 104 us-gaap_OtherInvestments |
Business days after the invoice date | 16 |  |
Days after the due date | 45 |  |
Wholesale accounts receivable written off | 0 por_Wholesaleaccountsreceivablewrittenoff | 0 por_Wholesaleaccountsreceivablewrittenoff | 0 por_Wholesaleaccountsreceivablewrittenoff
Margin deposit | 11 us-gaap_MarginDepositAssets | 9 us-gaap_MarginDepositAssets |
Letters of Credit Outstanding, Amount | 30 us-gaap_LettersOfCreditOutstandingAmount | 29 us-gaap_LettersOfCreditOutstandingAmount |
Expenses related to Cascade Crossing | 0 por_ExpensesrelatedtoCascadeCrossing | 52 por_ExpensesrelatedtoCascadeCrossing | 0 por_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 | 22 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest | 7 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest | 4 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedInterest
Allowance for equity funds used during construction | 37 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity | 13 us-gaap_PublicUtilitiesAllowanceForFundsUsedDuringConstructionCapitalizedCostOfEquity | 6 us-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 | 57 por_AssetRetirementRemovalCostsIncludedInDepreciationExpense | 55 por_AssetRetirementRemovalCostsIncludedInDepreciationExpense | 55 por_AssetRetirementRemovalCostsIncludedInDepreciationExpense
Finite-Lived Intangible Assets, Accumulated Amortization | 191 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization | 170 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization |
Amortization of Intangible Assets | 25 us-gaap_AmortizationOfIntangibleAssets | 22 us-gaap_AmortizationOfIntangibleAssets | 22 us-gaap_AmortizationOfIntangibleAssets
Future Amortization Expense, Year One | 35 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths |  |
Future Amortization Expense, Year Two | 33 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo |  |
Future Amortization Expense, Year Three | 29 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree |  |
Future Amortization Expense, Year Four | 28 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour |  |
Future Amortization Expense, Year Five | 22 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive |  |
Power Cost Deadband - Lower Threshold | 15 por_PowerCostDeadbandLowerThreshold |  |
Power Cost Deadband - Upper Threshold | 30 por_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 |  | 11 por_Netvariablepowercostoverrun |
Estimated Refund Under Power Cost Adjustment Mechanism | 0 por_EstimatedRefundUnderPowerCostAdjustmentMechanism | 0 por_EstimatedRefundUnderPowerCostAdjustmentMechanism | 0 por_EstimatedRefundUnderPowerCostAdjustmentMechanism
Actual Refund Under Power Cost Adjustment Mechanism |  | 0 por_ActualRefundUnderPowerCostAdjustmentMechanism | 0 por_ActualRefundUnderPowerCostAdjustmentMechanism
Franchise taxes | 42 por_FranchiseTaxes | 41 por_FranchiseTaxes | 42 por_FranchiseTaxes
Deferred Tax Assets, Regulatory Assets and Liabilities | 48 us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities | 33 us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities |
Noncurrent Regulatory Assets [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Deferred Tax Assets, Regulatory Assets and Liabilities | 86 us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities / us-gaap_RegulatoryAssetAxis = por_NoncurrentRegulatoryAssetsMember | 76 us-gaap_DeferredTaxAssetsRegulatoryAssetsAndLiabilities / us-gaap_RegulatoryAssetAxis = por_NoncurrentRegulatoryAssetsMember |
Noncurrent Regulatory Liabilities [Member] |  |  |
Property, Plant and Equipment [Line Items] |  |  |
Asset Retirement Obligations, Noncurrent | $ 39 us-gaap_AssetRetirementObligationsNoncurrent / us-gaap_RegulatoryLiabilityAxis = por_NoncurrentRegulatoryLiabilitiesMember | $ 39 us-gaap_AssetRetirementObligationsNoncurrent / us-gaap_RegulatoryLiabilityAxis = por_NoncurrentRegulatoryLiabilitiesMember |

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