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Regulatory Assets and Liabilities Schedule of Regulatory Assets and Liabilities (Details) - USD ($) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2020 | Dec. 31, 2019
Regulatory Assets [Line Items] |  |
Regulatory Assets | $ 593 | $ 500
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 506 |
Regulatory Liabilities | 1,392 | 1,421
Removal Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 0 |
Regulatory Liabilities | 1,016 | 1,021
Deferred Income Tax Charge [Member] |  |
Regulatory Assets [Line Items] |  |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 0 |
Regulatory Liabilities | 239 | 260
Asset Retirement Obligation Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 0 |
Regulatory Liabilities | $ 37 | 54
Revenue Subject to Refund [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Current Asset, End Date for Recovery | 2020 |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | $ 0 |
Regulatory Liabilities | 0 | 23
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory Assets [Line Items] |  |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 36 |
Regulatory Liabilities | 82 | 61
Regulatory Assets Earning a Rate of Return at the Approved Rate | 46 |
RemainingAmountsOfRegulatoryLiabilitesForWhichNoInterstAccruesDuringRecoveryPeriodIsProvided | 54 |
Deferred Derivative Gain (Loss) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets |  | 2
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 18 |
Regulatory Liabilities | 0 |
Earning a return [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Liabilities | 1,338 |
Other Regulatory Assets Earning a Return [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 87 |
Earning a return [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | $ 87 |
Deferred Derivative Gain (Loss) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Current Asset, End Date for Recovery | 2035 |
Regulatory Assets | $ 0 | 95
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 124 |
Pension and Other Postretirement Plans Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 0 | 213
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | $ 240 |
Loss on Reacquired Debt [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Current Asset, End Date for Recovery | 2050 |
Regulatory Assets | $ 0 | 26
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | $ 25 |
Environmental Restoration Costs [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Current Asset, End Date for Recovery | 2059 |
Regulatory Assets | $ 0 |
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | 95 | 94
Other Regulatory Assets (Liabilities) [Member] |  |
Regulatory Assets [Line Items] |  |
Regulatory Assets | 109 | $ 72
Remaining Amounts of Regulatory Assets for which No Return on Investment During Recovery Period is Provided | $ 22 |

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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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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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- Definition The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 Remaining balance of regulatory assets for which no return on investment during recovery is provided. In some cases, a regulator may permit an enterprise to include a cost that would be charged to expense by an unregulated enterprise as an allowable cost over a period of time by amortizing that cost for rate-making purposes, but the regulator does not include the unrecovered amount in the rate base. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -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 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 980 -SubTopic 340 -Section 55 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121594574&loc=d3e44360-110383 + Details
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