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Regulatory Assets and Liabilities (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Regulatory Assets and Liabilities Disclosure [Abstract] |  |
Regulatory Assets Earning a Return, Other Category | $ 33 por_RegulatoryAssetsEarningReturnOtherCategory | $ 16 por_RegulatoryAssetsEarningReturnOtherCategory
Regulatory Assets Earning a Return | 63 por_RegulatoryAssetsEarningReturn |
Regulatory Assets Earning a Rate of Return at the Cost of Debt | 19 por_RegulatoryAssetsEarningaRateofReturnattheCostofDebt |
Authorized Cost of Debt | 5.54%por_AuthorizedCostofDebt |
Regulatory Assets Earning a Rate of Return at the Cost of Capital | 2 por_RegulatoryAssetsEarningRateOfReturnAtCostOfCapital |
Authorized Cost of Capital | 7.65%por_AuthorizedCostOfCapital |
Regulatory Assets Earning a Rate of Return by Inclusion in Rate Base | 33 por_RegulatoryAssetsEarningRateOfReturnByInclusionInRateBase |
Regulatory Assets Earning a Rate of Return at the Approved Rate | 9 por_RegulatoryAssetsEarningRateOfReturnAtApprovedRate |
Approved Rate for Deferred Account Under Amortization, Low End of Range | 1.47%por_ApprovedRateForDeferredAccountUnderAmortizationLowEndOfRange |
Approved Rate for Deferred Accounts under Amortization, High End of Range | 1.77%por_ApprovedRateForDeferredAccountsUnderAmortizationHighEndOfRange |
Trojan ISFSI pollution control tax credits |  | $ 8 por_TrojanIsfsiPollutionControlTaxCredits

X
- Definition High end of the range of approved rates of return for amortizing deferred accounts (regulatory assets). + References No definition available. + Details
Name: | por_ApprovedRateForDeferredAccountsUnderAmortizationHighEndOfRange
Namespace Prefix: | por_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Low end of the range of approved rates of return for amortizing deferred accounts (regulatory assets). + References No definition available. + Details
Name: | por_ApprovedRateForDeferredAccountUnderAmortizationLowEndOfRange
Namespace Prefix: | por_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Authorized cost of capital rate. + References No definition available. + Details
Name: | por_AuthorizedCostOfCapital
Namespace Prefix: | por_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Authorized Cost of Debt + References No definition available. + Details
Name: | por_AuthorizedCostofDebt
Namespace Prefix: | por_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Regulatory Assets Earning a Rate of Return at the Cost of Debt + References No definition available. + Details
Name: | por_RegulatoryAssetsEarningaRateofReturnattheCostofDebt
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Regulatory assets earning a rate of return at the approved rate. + References No definition available. + Details
Name: | por_RegulatoryAssetsEarningRateOfReturnAtApprovedRate
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Regulatory assets earning a rate of return at the cost of capital. + References No definition available. + Details
Name: | por_RegulatoryAssetsEarningRateOfReturnAtCostOfCapital
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Regulatory assets earning a rate of return by inclusion in rate base. + References No definition available. + Details
Name: | por_RegulatoryAssetsEarningRateOfReturnByInclusionInRateBase
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Regulatory assets earning a rate of return. + References No definition available. + Details
Name: | por_RegulatoryAssetsEarningReturn
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Regulatory assets in 'other' category earning a rate of return. + References No definition available. + Details
Name: | por_RegulatoryAssetsEarningReturnOtherCategory
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Trojan ISFSI pollution control tax credits + References No definition available. + Details
Name: | por_TrojanIsfsiPollutionControlTaxCredits
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | us-gaap_RegulatoryAssetsAndLiabilitiesDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration