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Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2017 | Dec. 31, 2016
Regulatory Assets [Line Items] |  |
Remaining Recovery Period of Regulatory Assets, Price Risk Management | 6 years |
Regulatory Assets, Current | $ 62 | $ 36
Regulatory Assets, Noncurrent | 438 | 498
Regulatory Liability, Current | 31 | 51
Regulatory Liability, Noncurrent | $ 1,288 | 958
Remaining Recovery Period of Regulatory Asset, Debt Reacquisition Costs | 6 years |
Remaining refund period of regulatory liability, Trojan decommissioning activities | 5 years |
Removal Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Liability, Current | $ 0 | 0
Regulatory Liability, Noncurrent | 933 | 887
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Liability, Current | 28 | 33
Regulatory Liability, Noncurrent | 26 | 22
Asset Retirement Obligation Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Liability, Current | 0 | 0
Regulatory Liability, Noncurrent | 52 | 49
Environmental Restoration Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Liability, Current | 3 | 18
Regulatory Liability, Noncurrent | 0 | 0
Deferred Income Tax Charge [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Liability, Current | 0 | 0
Regulatory Liability, Noncurrent | 277 | 0
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | 9 | 10
Regulatory Assets, Noncurrent | 50 | 35
Loss on Reacquired Debt [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | 0 | 0
Regulatory Assets, Noncurrent | 19 | 22
Deferred Derivative Gain (Loss) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | 53 | 26
Regulatory Assets, Noncurrent | 151 | 120
Pension and Other Postretirement Plans Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | 0 | 0
Regulatory Assets, Noncurrent | 218 | 235
Deferred Income Tax Charge [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets, Current | 0 | 0
Regulatory Assets, Noncurrent | $ 0 | $ 86

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- Definition Remaining recovery period of regulatory assets, Price Risk Management, for which no return on investment during recovery period is provided. + References No definition available. + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are not expected to be recovered through revenue sources within one year or the normal operating cycle if longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382 + Details
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- Definition The amount for the individual regulatory current liability as itemized in a table of regulatory current liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 405 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6500807&loc=d3e48068-110394 + Details
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- Definition The amount for the individual regulatory noncurrent liability as itemized in a table of regulatory noncurrent liabilities as of the end of the period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.24) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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