Price Risk Management Collateral Posted With Counterparties Where Master Netting Arragements Exist (Details) (USD $) In Millions	Jun. 30, 2011	Dec. 31, 2010
Derivative, Collateral, Master Netting Arrangements, Letters of Credit	$ 17	$ 31

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por_DerivativeCollateralMasterNettingArrangementsLettersOfCredit

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xbrli:monetaryItemType

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