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Jointly-owned Plant Schedule of Jointly-owned plant (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Jointly Owned Utility Plant Interests [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman	65.00%
Jointly Owned Plant, Boardman Plant In Service Year	1980
Jointly Owned Utility Plant, Gross Ownership Amount of Boardman Plant In Service	$ 479
Jointly Owned Utility Plant, Ownership Amount of Boardman Plant Accumulated Depreciation	308
Jointly Owned Utility Plant Ownership Amount of Construction Work In Progress Boardman	8
Jointly Owned Utility Plant, Proportionate Ownership Share of Colstrip	20.00%
Jointly Owned Plant, Colstrip Plant In Service Year	1986
Jointly Owned Utility Plant, Gross Ownership Amount of Colstrip Plant In Service	507
Jointly Owned Utility Plant, Ownership Amount of Colstrip Plant Accumulated Depreciation	328
Jointly Owned Utility Plant Ownership Amount Of Construction Work In Progress Colstrip	3
Jointly Owned Utility Plant, Proportionate Ownership Share of Pelton/Round Butte	66.67%
Jointly Owned Plant, Pelton Plant in Service Year	1958
Jointly Owned Plant, Round Butte in Service Year	1964
Jointly Owned Utility Plant, Gross Ownership Amount of Pelton/Round Butte Plant In Service	215
Jointly Owned Utility Plant, Ownership Amount of Pelton/Round Butte Plant Accumulated Depreciation	48
Jointly Owned Utility Plant Ownership Amount Of Construction Work In Progress Pelton/Round Butte	5
Jointly Owned Utility Plant, Gross Ownership Amount of Plant in Service	1,201
Jointly Owned Utility Plant, Ownership Amount of Plant Accumulated Depreciation	684
Jointly Owned Utility Plant, Ownership Amount of Construction Work in Progress	$ 16

X

- Definition

Plant in service year for Boardman, a jointly owned plant by the reporting entity.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedPlantBoardmanPlantInServiceYear
Namespace Prefix:	por_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The plant in service year of Colstrip, a jointly owned plant by the reporting entity.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedPlantColstripPlantInServiceYear
Namespace Prefix:	por_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The plant in service year for Pelton, a jointly owned plant by the reporting entity.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedPlantPeltonInServiceYear
Namespace Prefix:	por_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The plant in service year for Round Butte, a jointly owned plant by the reporting entity.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedPlantRoundButteInServiceYear
Namespace Prefix:	por_
Data Type:	xbrli:gYearItemType
Balance Type:	na
Period Type:	instant

X

- Definition

The period end amount owned by the reporting entity of a jointly owned utility (Boardman) plant in service.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantGrossOwnershipAmountOfBoardmanPlantInService
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The period end amount owned by the reporting entity of a jointly owned utility (Colstrip) plant in service.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantGrossOwnershipAmountOfColstripPlantInService
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The period end amount owned by the reporting entity of utility plant (Pelton/Round Butte) plant in service.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantGrossOwnershipAmountOfPeltonroundButtePlantInService
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The period end amount owned by the reporting entity of a jointly owned electricity generating facility (Boardman) plant accumulated depreciation.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantOwnershipAmountOfBoardmanPlantAccumulatedDepreciation
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The period end amount owned by the reporting entity of a jointly owned electricity generating facility (Colstrip) plant accumulated depreciation.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantOwnershipAmountOfColstripPlantAccumulatedDepreciation
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The reporting entity's period end amount of construction work in progress at Boardman, a jointly owned electricity generation plant.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgressBoardman
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The reporting entity's period end amount of construction work in progress at Colstrip, a jointly owned electricity generation plant.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgressColstrip
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The reporting entity's period end amount of construction work in progress at Pelton/Round Butte, a jointly owned electricity generation plant.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantOwnershipAmountOfConstructionWorkInProgressPeltonroundButte
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The period end amount owned by the reporting entity of a jointly owned electricity generating facility (Pelton/Round Butte) plant accumulated depreciation.

+ References

No definition available.

+ Details

Name:	por_JointlyOwnedUtilityPlantOwnershipAmountOfPeltonroundButtePlantAccumulatedDepreciation
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

The proportionate share of the reporting entity's interest (percent) in Boardman, a jointly owned utility plant.

+ References

No definition available.

+ Details

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

X

- Definition

The proportionate share of the reporting entity's interest (percent) in Colstrip, a jointly owned utility plant.

+ References

No definition available.

+ Details

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

X

- Definition

The reporting entity's interest (percent) in Pelton/Round/Butte, a jointly owned utility plant.

+ References

No definition available.

+ Details

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

X

- Definition

The period end amount owned by the reporting utility of a jointly owned utility plant in service.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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Namespace Prefix:	us-gaap_
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- Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

The period end amount of construction work in progress at a jointly owned electricity generation plant.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

The period end amount of accumulated depreciation in a jointly owned electricity generation plant.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 980

-SubTopic 360

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 10.C)

-URI http://asc.fasb.org/extlink&oid=6500719&loc=d3e659983-123033



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 10

-Section C

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