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Regulatory Assets and Liabilities (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($)
Regulatory Assets and Liabilities Disclosure [Abstract] |
Regulatory Assets Earning a Rate of Return at the Approved Rate | $ 1,384
Increase in net deferred tax regulatory liabilitily | $ 357

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- Definition Increase in net deferred tax regulatory liability resulting from the Tax Cuts and Jobs Act of 2017. + References No definition available. + Details
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- Definition Regulatory assets earning a rate of return at the approved rate. + References No definition available. + Details
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Namespace Prefix: | por_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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