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Balance Sheet Components (Tables) | 12 Months Ended
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Dec. 31, 2018
Balance Sheet Components [Abstract] |
SEC Schedule, 12-09, Schedule of Valuation and Qualifying Accounts Disclosure [Text Block] | The following is the activity in the allowance for uncollectible accounts (in millions):
| Years Ended December 31,
| 2018 |  | 2017 |  | 2016
Balance as of beginning of year | $ | 6 |  |  | $ | 6 |  |  | $ | 6 |
Increase in provision | 14 |  |  | 6 |  |  | 5 |
Amounts written off, less recoveries | (5 | ) |  | (6 | ) |  | (5 | )
Balance as of end of year | $ | 15 |  |  | $ | 6 |  |  | $ | 6 |
Investments held in trust [Table Text Block] | The trusts are comprised of the following investments as of December 31 (in millions):
| Nuclear Decommissioning Trust |  | Non-Qualified Benefit Plan Trust
| 2018 |  | 2017 |  | 2018 |  | 2017
Cash equivalents | $ | 7 |  |  | $ | 25 |  |  | $ | 2 |  |  | $ | 1 |
Marketable securities, at fair value: |  |  |  |  |  |  |
Equity securities | — |  |  | — |  |  | 6 |  |  | 7 |
Debt securities | 35 |  |  | 17 |  |  | 1 |  |  | 1 |
Insurance contracts, at cash surrender value | — |  |  | — |  |  | 27 |  |  | 28 |
| $ | 42 |  |  | $ | 42 |  |  | $ | 36 |  |  | $ | 37 |
Schedule of Other Assets and Other Liabilities [Table Text Block] | Other current assets and Accrued expenses and other current liabilities consist of the following (in millions):
| As of December 31,
| 2018 |  | 2017
Other current assets: |  |  |
Prepaid expenses | $ | 54 |  |  | $ | 50 |
Margin deposits | 16 |  |  | 11 |
Assets from price risk management activities | 20 |  |  | 6 |
Other | — |  |  | 6 |
| $ | 90 |  |  | $ | 73 |
Accrued expenses and other current liabilities: |  |  |
Regulatory liabilities—current | $ | 36 |  |  | $ | 31 |
Accrued employee compensation and benefits | 66 |  |  | 60 |
Accrued dividends payable | 34 |  |  | 31 |
Accrued interest payable | 27 |  |  | 27 |
Accrued taxes payable | 34 |  |  | 31 |
Other | 71 |  |  | 61 |
| $ | 268 |  |  | $ | 241 |

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- Definition The entire disclosure for valuation and qualifying accounts and reserves. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Subsection 09 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 4 -Subparagraph (SX 210.12-09) -URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e24092-122690 + Details
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