Risk Management Counterparties Representing 10% or More of Assets and Liabilities from price risk management activities (Details)	Sep. 30, 2019	Dec. 31, 2018
Assets from price risk management activities:
Counterparty A	35.00%	42.00%
Counterparty B	0.00%	15.00%
Counterparty C	17.00%	5.00%
Counterparty D	11.00%	9.00%
Concentration of Risk, Derivative Instruments, Assets	63.00%	71.00%
Liabilities from price risk management activities:
Counterparty C	76.00%	56.00%

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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- 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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- Definition

Counterparty D

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- Definition

Liabilities from price risk management activities: [Abstract]

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