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Long term debt (Details) - USD ($) $ in Millions | 1 Months Ended | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | ---
Aug. 31, 2017 | Jan. 31, 2016 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Nov. 27, 2017 | Oct. 30, 2017 | Aug. 21, 2017
Debt Instrument [Line Items] |  |  |  |  |  |  |  |
Proceeds from Issuance of First Mortgage Bond |  |  | $ 225 |  |  |  |  |
Repayments of Debt |  |  | 150 |  |  |  |  |
Debt Instrument, Face Amount |  |  |  |  |  | $ 75 | $ 25 | $ 50
Long-term Pollution Control Bond |  |  | $ 21 |  |  |  |  |
Debt Instrument, Interest Rate, Stated Percentage |  |  | 3.98% |  |  |  |  |
Proceeds from Issuance of Long-term Debt | $ 75 | $ 150 | $ 225 | $ 290 | $ 145 |  |  |
First mortgage Bonds - minimum rate |  |  | 2.51% |  |  |  |  |
Unsecured Debt, Current |  |  | $ 0 | $ 150 |  |  |  |
First Mortgage Bonds - maximum rate |  |  | 9.31% |  |  |  |  |
Debt, Weighted Average Interest Rate |  |  | 5.03% | 4.86% |  |  |  |
Line of Credit Facility, Interest Rate During Period |  |  |  | 1.37% |  |  |  |
Line of Credit Facility, Interest Rate at Period End |  |  | 1.87% | 5.00% |  |  |  |
Line of Credit Facility, Commitment Fee Percentage |  |  | 0.00% |  |  |  |  |
Pollution Control Revenue Bonds owned by PGE |  |  | $ 21 | $ 21 |  |  |  |

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- Definition First mortgage Bonds - minimum rate + References No definition available. + Details
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- Definition Pollution Control Revenue Bonds owned by PGE + References No definition available. + Details
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- Definition Remarketable Pollution Control Bonds held by the Company. + References No definition available. + Details
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- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=64930739&loc=d3e28878-108400 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28551-108399 + Details
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- Definition The cash inflow from amounts received from a long-term debt instrument secured by a first mortgage deed of trust, containing a pledge of real property. The lender has the highest claim on the property in case of default. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 14 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3255-108585 + Details
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