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Nuclear Decommissioning Trust Fund (Tables) | 3 Months Ended
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Mar. 31, 2019
Nuclear Decommissioning Trust Fund Disclosure [Abstract] |
Summary of aggregate fair values and unrealized gains and losses (including other-than-temporary impairments) for the securities held in the nuclear decommissioning trust fund | The following table summarizes the aggregate fair values and unrealized gains and losses for the securities held in the trust funds, as well as information about the contractual maturities of those securities.
| As of March 31, 2019 |  | As of December 31, 2018
(In millions, except maturities) | Fair Value |  | Unrealized Gains |  | Unrealized Losses |  | Weighted-average Maturities (In years) |  | Fair Value |  | Unrealized Gains |  | Unrealized Losses |  | Weighted-average Maturities (In years)
Cash and cash equivalents | $ | 15 |  |  | $ | — |  |  | $ | — |  |  | — |  |  | $ | 19 |  |  | $ | — |  |  | $ | — |  |  | — |
U.S. government and federal agency obligations | 50 |  |  | 2 |  |  | — |  |  | 13 |  |  | 46 |  |  | 1 |  |  | — |  |  | 12 |
Federal agency mortgage-backed securities | 96 |  |  | 1 |  |  | 1 |  |  | 25 |  |  | 100 |  |  | 1 |  |  | 2 |  |  | 23 |
Commercial mortgage-backed securities | 29 |  |  | 1 |  |  | — |  |  | 23 |  |  | 22 |  |  | — |  |  | 1 |  |  | 22 |
Corporate debt securities | 100 |  |  | 3 |  |  | 1 |  |  | 11 |  |  | 96 |  |  | 1 |  |  | 2 |  |  | 11 |
Equity securities | 424 |  |  | 276 |  |  | — |  |  | — |  |  | 376 |  |  | 231 |  |  | 1 |  |  | — |
Foreign government fixed income securities | 4 |  |  | — |  |  | — |  |  | 10 |  |  | 4 |  |  | — |  |  | — |  |  | 9 |
Total | $ | 718 |  |  | $ | 283 |  |  | $ | 2 |  |  |  |  | $ | 663 |  |  | $ | 234 |  |  | $ | 6 |  |  |
Summary of proceeds from sales of available-for-sale securities and the related realized gains and losses | The following table summarizes proceeds from sales of available-for-sale securities and the related realized gains and losses from these sales. The cost of securities sold is determined on the specific identification method.
| Three months ended March 31,
| 2019 |  | 2018
| (In millions)
Realized gains | $ | 3 |  |  | $ | 3 |
Realized losses | (2 | ) |  | (3 | )
Proceeds from sale of securities | 113 |  |  | 182 |

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- Definition Disclosure related to investments held in a trust fund to pay for the costs of decommissioning facilities. + References No definition available. + Details
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- Definition -- None. No documentation exists for this element. -- + References No definition available. + Details
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- Definition Tabular disclosure of the proceeds from sales of available-for-sale securities and the gross realized gains and gross realized losses that have been included in earnings as a result of those sales. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 9 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27357-111563 + Details
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