Risk Management Counterparties Representing 10% or More of Assets and Liabilities from price risk management activities (Details)	Sep. 30, 2018	Dec. 31, 2017
Assets from price risk management activities:
Counterparty A	58.00%	39.00%
Counterparty B	3.00%	12.00%
Total	61.00%	51.00%
Liabilities from price risk management activities:
Counterparty C	67.00%	62.00%
Total	67.00%	62.00%

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.

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No definition available.

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- Definition

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

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No definition available.

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- Definition

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

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No definition available.

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Name:	por_CounterpartyA
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- Definition

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

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No definition available.

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Name:	por_CounterpartyB
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- Definition

Counterparty D for PRM Liab

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No definition available.

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- Definition

Liabilities from price risk management activities: [Abstract]

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No definition available.

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