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SAN ONOFRE NUCLEAR GENERATING STATION (SONGS) - NUCLEAR DECOMMISSIONING TRUSTS (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | $ 731 | $ 701 |
Gross unrealized gains | 259 | 336 |
Gross unrealized losses | (16) | (4) |
Estimated fair value | 974 | 1,033 |
Proceeds from sales | 890 | 1,314 | $ 1,134
Gross realized gains | 42 | 157 | 111
Gross realized losses | (10) | (14) | $ (29)
Debt Securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | 556 | 514 |
Gross unrealized gains | 6 | 10 |
Gross unrealized losses | (6) | (3) |
Estimated fair value | 556 | 521 |
Debt securities issued by the U.S. Treasury and other U.S. government corporations and agencies [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | 52 | 54 |
Gross unrealized gains | 1 | 0 |
Gross unrealized losses | 0 | 0 |
Estimated fair value | 53 | 54 |
Municipal bonds [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | 266 | 245 |
Gross unrealized gains | 4 | 7 |
Gross unrealized losses | (1) | (2) |
Estimated fair value | 269 | 250 |
Other securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | 238 | 215 |
Gross unrealized gains | 1 | 3 |
Gross unrealized losses | (5) | (1) |
Estimated fair value | 234 | 217 |
Equity securities [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | 168 | 171 |
Gross unrealized gains | 253 | 326 |
Gross unrealized losses | (10) | (1) |
Estimated fair value | 411 | 496 |
Cash and cash equivalents [Member] |  |  |
Debt Securities, Available-for-sale [Line Items] |  |  |
Cost | 7 | 16 |
Gross unrealized gains | 0 | 0 |
Gross unrealized losses | 0 | 0 |
Estimated fair value | $ 7 | $ 16 |

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