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

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.

No definition available.

Name:	por_VolumeRelatedToDerivativeInstrumentsAtBalanceSheetDateCommodityContractsNaturalGas
Namespace Prefix:	por_
Data Type:	num:energyItemType
Balance Type:	na
Period Type:	instant