Price Risk Management Counterparties Representing 10% or More of Assets and Liabilities from price risk management activities (Details)	Mar. 31, 2018	Dec. 31, 2017
Assets from price risk management activities:
Counterparty A	15.00%	39.00%
Counterparty B	18.00%	12.00%
Counterparty C	10.00%	1.00%
Counterparty D	17.00%	7.00%
Counterparty E	10.00%	6.00%
Total	70.00%	65.00%
Liabilities from price risk management activities:
Counterparty F	58.00%	62.00%
Total	58.00%	62.00%

Assets from price risk management activities: [Abstract]

No definition available.

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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.

+ Details

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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

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_CounterpartyC
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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_CounterpartyD
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- Definition

Counterparty D for PRM Liab

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No definition available.

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Name:	por_CounterpartyDforPRMLiab
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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_CounterpartyE
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- Definition

Liabilities from price risk management activities: [Abstract]

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No definition available.

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