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Investments | 12 Months Ended
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Dec. 31, 2018
Regulated Entity, Other Assets, Noncurrent [Abstract] |
Investments | Investments Nuclear Decommissioning Trusts Future decommissioning costs related to SCE's nuclear assets are expected to be funded from independent decommissioning trusts. The following table sets forth amortized cost and fair value of the trust investments (see Note 4 for a discussion of fair value of the trust investments):
| Longest Maturity Date |  | Amortized Cost |  | Fair Value
|  | December 31,
(in millions) |  | 2018 |  | 2017 |  | 2018 |  | 2017
Stocks | — |  | * |  |  | $ | 236 |  |  | $ | 1,381 |  |  | $ | 1,596 |
Municipal bonds | 2057 |  | 665 |  |  | 643 |  |  | 767 |  |  | 768 |
U.S. government and agency securities | 2067 |  | 1,193 |  |  | 1,235 |  |  | 1,288 |  |  | 1,319 |
Corporate bonds | 2050 |  | 573 |  |  | 579 |  |  | 611 |  |  | 643 |
Short-term investments and receivables/payables 1 | One-year |  | 70 |  |  | 110 |  |  | 73 |  |  | 114 |
Total |  |  | $ | 2,501 |  |  | $ | 2,803 |  |  | $ | 4,120 |  |  | $ | 4,440 |
* Effective January 1, 2018, SCE adopted an accounting standards update related to the classification and measurement of financial instruments in which equity investments are measured at fair value. See Note 1 for further information.
1 | Short-term investments include $71 million and $29 million of repurchase agreements payable by financial institutions which earn interest, are fully secured by U.S. Treasury securities and mature by January 2, 2019 and January 2, 2018 as of December 31, 2018 and 2017, respectively.
Trust fund earnings (based on specific identification) increase the trust fund balance and the ARO regulatory liability. Unrealized holding gains, net of losses, were $1.4 billion and $1.6 billion at December 31, 2018 and 2017, respectively, and other-than-temporary impairments of $170 million and $143 million at the respective periods. Trust assets are used to pay income taxes. Deferred tax liabilities related to net unrealized gains at December 31, 2018 were $323 million. Accordingly, the fair value of trust assets available to pay future decommissioning costs, net of deferred income taxes, totaled $3.8 billion at December 31, 2018. The following table summarizes the gains and (losses) for the trust investments:
| December 31,
(in millions) | 2018 | 2017 | 2016
Gross realized gains | $ | 134 |  | $ | 244 |  | $ | 92 |
Gross realized losses | (27 | ) | (23 | ) | (19 | )
Net unrealized (losses) gains for equity securities | (233 | ) | 142 |  | 75 |
Due to regulatory mechanisms, changes in assets of the trusts from income or loss items have no impact on operating revenue or earnings.

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