Equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Jun. 30, 2013
Equity [Abstract]
Share Price		$ 29.50us-gaap_SharePrice
Equity Forward Sale Agreement, Settlement Threshold	10,400,000
Equity Forward Sale Agreement future settlement amount	$ 272
Option Indexed to Issuer's Equity, Settlement Alternatives, Cash, at Fair Value	114
Net share settlement	3,074,000por_Netsharesettlement
Proceeds from Issuance of Common Stock	$ 0

Funds that would be received undter the equity forward sale agreement in the future.

No definition available.

Name:	por_Equityforwardsaleagreementfuturesettlementamount
Namespace Prefix:	por_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Shares required to contractually settle Equity forward sale agreement requirements.

+ References

No definition available.

+ Details

Name:	por_EquityForwardSaleAgreementSettlementThreshold
Namespace Prefix:	por_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Net share settlement

+ References

No definition available.

+ Details

Name:	por_Netsharesettlement
Namespace Prefix:	por_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Details

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

- Definition

Fair value of each cash settlement alternative for each freestanding option contract.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 815

-SubTopic 40

-Section 50

-Paragraph 5

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=6445032&loc=d3e90205-114008

+ Details

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

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Price of a single share of a number of saleable stocks of a company.

+ References

No definition available.

+ Details

Name:	us-gaap_SharePrice
Namespace Prefix:	us-gaap_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	instant