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Schedule of Asset Retirement Obligations (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Dec. 31, 2011
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Asset Retirement Obligation Disclosure [Abstract] |  |  |  |
Trojan decommissioning activities | $ 41 por_TrojanDecommissioningActivities | $ 41 por_TrojanDecommissioningActivities |  |
Utility plant | 64 por_AssetRetirementObligationUtilityPlant | 49 por_AssetRetirementObligationUtilityPlant |  |
Non-utility property | 11 por_AssetRetirementObligationNonUtilityProperty | 10 por_AssetRetirementObligationNonUtilityProperty |  |
Asset Retirement Obligation | $ 116 us-gaap_AssetRetirementObligation | $ 100 us-gaap_AssetRetirementObligation | $ 94 us-gaap_AssetRetirementObligation | $ 87 us-gaap_AssetRetirementObligation

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- Definition Asset Retirement Obligation - Non-utility property + References No definition available. + Details
Name: | por_AssetRetirementObligationNonUtilityProperty
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Asset Retirement Obligation - Utility Plant + References No definition available. + Details
Name: | por_AssetRetirementObligationUtilityPlant
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Asset retirement obligation related to Trojan decommissioning activities + References No definition available. + Details
Name: | por_TrojanDecommissioningActivities
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The carrying amount of a liability for an asset retirement obligation. An asset retirement obligation is a legal obligation associated with the disposal or retirement of a tangible long-lived asset that results from the acquisition, construction or development, or the normal operations of a long-lived asset, except for certain obligations of lessees. + 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) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Asset Retirement Obligation -URI http://asc.fasb.org/extlink&oid=6505190 + Details
Name: | us-gaap_AssetRetirementObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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