Fair Value of Financial Instruments Financial Assets and Liabilities Recognized at Fair Value (Details) - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Nuclear decommissioning trust: (1)
Money market funds	$ 16	$ 65
Debt securities:
Domestic government	13	14
Corporate credit	11	11
Equity securities:
Domestic	7	5
International		1
Debt securities—domestic government	1
Assets from price risk management activities: (1) (3)
Electricity	4	5
Natural gas	0	2
Total	52	103
Liabilities from price risk management activities: (1) (3)
Electricity	152	112
Natural gas	136	116
Total	288	228
Fair Value, Inputs, Level 1 [Member]
Nuclear decommissioning trust: (1)
Money market funds	0	0
Debt securities:
Domestic government	4	7
Corporate credit	0	0
Equity securities:
Domestic	5	4
International		1
Debt securities—domestic government	1
Assets from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	10	12
Liabilities from price risk management activities: (1) (3)
Electricity	0	0
Natural gas	0	0
Total	0	0
Fair Value, Inputs, Level 2 [Member]
Nuclear decommissioning trust: (1)
Money market funds	16	65
Debt securities:
Domestic government	9	7
Corporate credit	11	11
Equity securities:
Domestic	2	1
International		0
Debt securities—domestic government	0
Assets from price risk management activities: (1) (3)
Electricity	3	4
Natural gas	0	2
Total	41	90
Liabilities from price risk management activities: (1) (3)
Electricity	20	32
Natural gas	99	95
Total	119	127
Fair Value, Inputs, Level 3 [Member]
Nuclear decommissioning trust: (1)
Money market funds	0	0
Debt securities:
Domestic government	0	0
Corporate credit	0	0
Equity securities:
Domestic	0	0
International		0
Debt securities—domestic government	0
Assets from price risk management activities: (1) (3)
Electricity	1	1
Natural gas	0	0
Total	1	1
Liabilities from price risk management activities: (1) (3)
Electricity	132	80
Natural gas	37	21
Total	$ 169	$ 101

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

Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to purchases or sales of electricity.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of the asset arising from commodity contracts related to purchases or sales of natural gas.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of electricity.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount as of the balance sheet date of the liabilities arising from commodity contracts related to purchases or sales of natural gas.

+ References

No definition available.

+ Details

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

- Definition

Common stock asset securities held in Non-qualified benefit plan trust, which are carried at fair value

+ References

No definition available.

+ Details

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

- Definition

Debt securities: [Abstract]

+ References

No definition available.

+ Details

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

- 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

- Definition

Debt mutual funds assets in the Non-qualified benefit plan trust, which are carried at fair value.

+ References

No definition available.

+ Details

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

- Definition

Equity mutual fund assets held in the Non-qualified benefit plan trust, which are carried at fair value.

+ References

No definition available.

+ Details

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

- Definition

Nuclear decommissioning trust: [Abstract]

+ References

No definition available.

+ Details

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

- Definition

The aggregate fair value as of the balance sheet date of financial instruments and other positions owned by the entity including: (1) mortgages, mortgage-backed and asset backed securities; (2) US government and agency obligations; (3) state and municipal government obligations; (4) other sovereign government debt; (5) corporate obligations; (6) corporate equities; (7) principal investments; (8) derivative contracts; and (9) physical commodities. Includes both pledged and unpledged holdings.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 940

-SubTopic 320

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=35711157&loc=d3e42546-110969

+ Details

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

- Definition

The fair value as of the balance sheet date of firm holdings in fixed income or other debt securities issued by a corporation or other issuer not elsewhere specified in the taxonomy. Includes both pledged (to counterparties as collateral for financing transactions) and unpledged holdings.

+ References

+ Details

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

- Definition

Fair value of financial and nonfinancial obligations.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

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

- Definition

Debt (bills, notes or bonds) that are issued by the government of the United States which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: