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Price Risk Management Schedule of Notional Amounts of Outstanding Derivative Positions (Details) | Dec. 31, 2011 MMBTU MWh | Dec. 31, 2010 MWh MMBTU
--- | --- | ---
Commodity contracts: [Abstract] |  |
Electricity | 13,000,000 | 9,000,000
Volume Related to Derivative Instruments at Balance Sheet Date Commodity Contracts Natural Gas | 79,000,000 | 93,000,000

X
- Details
Name: | por_CommodityContractsAbstract
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

X
- Definition Net volume related to the reporting entity's derivative instruments as of the balance sheet date having arisn 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