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Risk Management Net volumes related to price risk management activities (Details) MWh in Millions, MMBTU in Millions, $ in Millions | Sep. 30, 2018 CAD ($) MMBTU MWh | Dec. 31, 2017 CAD ($) MMBTU MWh
--- | --- | ---
Commodity contracts: |  |
Electricity | MWh | 6 | 7
Natural gas | MMBTU | 115 | 114
Foreign currency | $ | $ 20 | $ 21

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- Definition Commodity contracts: [Abstract] + References No definition available. + Details
Name: | por_CurrentAssetsCommodityContractsAbstract
Namespace Prefix: | por_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Net volume associated with the reporting entity's derivative instruments recorded as of the balance sheet date having arisen from price risk management activities related to natural gas. + References No definition available. + Details
Name: | por_VolumeRelatedToDerivativeInstrumentsAtBalanceSheetDateCommodityContractsNaturalGas
Namespace Prefix: | por_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | instant

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- Definition Net volume related to the reporting entity's derivative instruments as of the balance sheet date having arisen from price risk management activities. + References No definition available. + Details
Name: | por_VolumeRelatedToDerivativeInstrumentsHeldAtBalanceSheetDateCommodityContractsElectricity
Namespace Prefix: | por_
Data Type: | num:energyItemType
Balance Type: | na
Period Type: | instant

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- Definition Net amount associated with the reporting entity's derivative instruments recorded as of the balance sheet date having arisen from price risk management activities related to foreign currency. + References No definition available. + Details
Name: | por_VolumeRelatedtoDerivativeInstrumentsHeldatBalanceSheetDateForeignCurrency
Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant