Price Risk Management Counterparties Representing 10% or More (Details)	Sep. 30, 2011	Dec. 31, 2010
Assets from price risk management activities:
Counterparty A	18.00%	23.00%
Counterparty B	14.00%	1.00%
Counterparty C	12.00%	5.00%
Counterparty D	9.00%	22.00%
Counterparty E	3.00%	11.00%
Counterparty F	0.00%	10.00%
Concentration of Risk, Derivative Instruments, Assets	56.00%	72.00%
Liabilities from price risk management activities:
Counterparty A	25.00%	24.00%
Counterparty G	10.00%	12.00%
Concentration of Risk, Derivative Instruments, Liabilities	35.00%	36.00%

Assets from price risk management activities: [Abstract]

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- Definition

Represents aggregate of individually significant counterparties of total assets arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Represents aggregate of individually significant counterparties of total liabilities arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total assets arising from dreivative instruments from price risk management activities.

+ Details

Name:	por_CounterpartyD
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- Definition

Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total assets arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total liabilities arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Individually significant counterparty of total liabilities arising from derivative instruments from price risk management activities.

+ Details

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- Definition

Liabilities from price risk management activities: [Abstract]

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