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Asset Retirement Obligations (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2019 | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Asset Retirement Obligation, Revision of Estimate | $ 69 | $ 82 | $ 27 | $ 0
Asset Retirement Obligation, Accretion Expense |  | 9 | 8 | 7
Asset Retirement Obligation, Liabilities Incurred |  | 0 | 0 | $ 2
Asset Retirement Obligation, Period Increase (Decrease) |  | $ 14 |  |
Document Period End Date |  | Dec. 31, 2019 |  |
Decommissioning Liability, Noncurrent |  | $ 4 |  |
Asset Retirement Obligation, Cash Paid to Settle |  | 4 |  |
Recorded Third-Party Environmental Recoveries, Amount |  | 4 | $ 4 |
Non Utility [Member] [Member] |  |  |  |
Asset Retirement Obligation, Revision of Estimate | $ 13 |  |  |
Utility Plant [Domain] |  |  |  |
Asset Retirement Obligation, Accretion Expense |  | 4 |  |
Asset Retirement Obligation, Liabilities Incurred |  | 3 |  |
Colstrip [Member] |  |  |  |
Asset Retirement Obligation, Period Increase (Decrease) |  | $ 11 |  |

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- Definition The end date of the period reflected on the cover page if a periodic report. For all other reports and registration statements containing historical data, it is the date up through which that historical data is presented. If there is no historical data in the report, use the filing date. The format of the date is CCYY-MM-DD. + References No definition available. + Details
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- Definition Amount of accretion expense recognized during the period that is associated with an asset retirement obligation. Accretion expense measures and incorporates changes due to the passage of time into the carrying amount of the liability. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6392676&loc=d3e7480-110848 + Details
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- Definition Amount of cash paid during the period to settle an asset retirement obligation. Amounts paid to settle an asset retirement obligation are generally included in the operating section of the Statement of Cash Flows. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 17 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=118932676&loc=d3e3367-108585 + Details
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- Definition Amount of asset retirement obligations incurred during the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(1) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in asset retirement obligations. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of increase (decrease) in the asset retirement obligation from changes in the amount or timing of the estimated cash flows associated with the settlement of the obligation. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 35 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6392603&loc=d3e7123-110846 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c)(4) -URI http://asc.fasb.org/extlink&oid=6392692&loc=d3e7535-110849 + Details
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- Definition Amount of a decommissioning liability associated with a legal obligation that a firm incurs when it constructs or operates an asset that must eventually be withdrawn from active service. This may include operating assets such as nuclear power plants or shipping vessels. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 450 -SubTopic 20 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 5.Y.Q2) -URI http://asc.fasb.org/extlink&oid=27011672&loc=d3e149879-122751 + Details
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- Definition Recorded amount of the individual components comprising the asset for third-party recoveries related to environmental remediation obligations. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 410 -SubTopic 30 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=109237650&loc=d3e13022-110858 + Details
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