Risk Management Counterparties Representing 10% or More of Assets and Liabilities from price risk management activities (Details)	Mar. 31, 2019	Dec. 31, 2018
Assets from price risk management activities:
Counterparty A	33.00%	42.00%
Counterparty B	11.00%	15.00%
Counterparty C	13.00%	9.00%
Concentration of Risk, Derivative Instruments, Assets	57.00%	66.00%
Liabilities from price risk management activities:
Counterparty D	62.00%	56.00%

Assets from price risk management activities: [Abstract]

No definition available.

Name:	por_AssetsFromPriceRiskManagementActivitiesAbstract
Namespace Prefix:	por_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ References

No definition available.

+ Details

Name:	por_ConcentrationOfRiskDerivativeInstrumentsAssets
Namespace Prefix:	por_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	por_ConcentrationOfRiskDerivativeInstrumentsLiabilities
Namespace Prefix:	por_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	por_CounterpartyA
Namespace Prefix:	por_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	por_CounterpartyB
Namespace Prefix:	por_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ References

No definition available.

+ Details

Name:	por_CounterpartyC
Namespace Prefix:	por_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Liabilities from price risk management activities: [Abstract]

+ References

No definition available.

+ Details

Name:	por_LiabilitiesFromPriceRiskManagementActivitiesAbstract
Namespace Prefix:	por_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration