Jointly-owned Plant Jointly Owned Plant (Details) (USD $)	1 Months Ended	3 Months Ended	12 Months Ended
Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013	Dec. 31, 1985
Property, Plant and Equipment [Line Items]
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman transferred	10.00%	10.00%	10.00%	15.00%			15.00%
Property, Plant and Equipment, Additions	$ 7,000,000	$ 7,000,000	$ 7,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Inventory	4,000,000	4,000,000	4,000,000
Asset Retirement Obligation, Liabilities Incurred	7,000,000	8,000,000	15,000,000	4,000,000	0
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities	6,000,000	6,000,000	6,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities	4,000,000	4,000,000	4,000,000
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities	2,000,000	2,000,000	2,000,000
Asset Retirement Obligation Increase related to Boardman plant				7,000,000
Interest in Pacific Northwest Intertie							10.714%por_InterestinPacificNorthwestIntertie
Significant Acquisitions and Disposals, Acquisition Costs or Sale Proceeds	$ 8,000,000	$ 8,000,000	$ 8,000,000	$ 1
Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman	90.00%	90.00%	90.00%	80.00%		65.00%

Asset Retirement Obligation Increase related to Boardman plant due to updated decommissioning study.

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Interest in Pacific Northwest Intertie

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- Definition

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

+ References

No definition available.

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Jointly Owned Utility Plant, Proportionate Ownership Share of Boardman transferred

+ References

No definition available.

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- Definition

Amount of asset retirement obligations incurred during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 410

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)(1)

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Amount of liabilities due within one year or within the normal operating cycle, if longer, assumed at the acquisition date.

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Amount of tangible personal property used to produce goods and services, including, but is not limited to, tools, dies and molds, computer and office equipment, acquired at the acquisition date.

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The amount of financial liabilities assumed (as defined) which have been recognized as of the acquisition date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=39739317&loc=d3e4845-128472

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 10

-Section 55

-Paragraph 37

-URI http://asc.fasb.org/extlink&oid=35744172&loc=d3e2207-128464

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financial Liability

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The amount of inventory recognized as of the acquisition date.

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Amount of liabilities due after one year or the normal operating cycle, if longer, assumed at the acquisition date.

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- Definition

The value of all consideration given or received by the Entity in the significant acquisition or disposal.

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