Price Risk Management Counterparties Representing 10% or More of Assets and Liabilities from price risk management activities (Details)	Jun. 30, 2016	Dec. 31, 2015
Assets from price risk management activities:
Counterparty A	22.00%	5.00%
Counterparty B	21.00%	59.00%
Counterparty C	6.00%	10.00%
Total	49.00%	74.00%
Liabilities from price risk management activities:
Counterparty D	57.00%	36.00%
Counterparty B	9.00%	10.00%
Counterparty E	7.00%	10.00%
Total	73.00%	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 liabilities arising from derivative instruments from price risk management activities.

+ References

No definition available.

+ Details

Name:	por_CounterpartyBforPRMLiabs
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

Counterparty D for PRM Liab

+ References

No definition available.

+ Details

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

- Definition

Counterparty E For PRM Liab

+ References

No definition available.

+ Details

Name:	por_CounterpartyEForPRMLiab
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