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Investments | 3 Months Ended
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Mar. 31, 2019
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 Dates |  | Amortized Cost |  | Fair Value
(in millions) |  | March 31, 2019 |  | December 31, 2018 |  | March 31, 2019 |  | December 31, 2018
Stocks | — |  | * |  |  | * |  |  | $ | 1,550 |  |  | $ | 1,381 |
Municipal bonds | 2057 |  | 662 |  |  | 665 |  |  | 785 |  |  | 767 |
U.S. government and agency securities | 2067 |  | 1,116 |  |  | 1,193 |  |  | 1,224 |  |  | 1,288 |
Corporate bonds | 2050 |  | 549 |  |  | 573 |  |  | 603 |  |  | 611 |
Short-term investments and receivables/payables 1 | One-year |  | 124 |  |  | 70 |  |  | 129 |  |  | 73 |
Total |  |  | $ | 2,451 |  |  | $ | 2,501 |  |  | $ | 4,291 |  |  | $ | 4,120 |
* | Equity investments are measured at fair value.
1 | Short-term investments include $35 million and $71 million of repurchase agreements payable by financial institutions which earn interest, are fully secured by U.S. Treasury securities and mature by April 1, 2019 and January 2, 2019 as of March 31, 2019 and December 31, 2018, respectively.
Trust fund earnings (based on specific identification) increase the trust fund balance and the asset retirement obligation ("ARO") regulatory liability. Unrealized holding gains, net of losses, were$1.6 billion and $1.4 billion at March 31, 2019 and December 31, 2018, respectively, and other-than-temporary impairments of $162 million and $170 million at the respective periods. Trust assets are used to pay income taxes arising from trust investing activity. Deferred tax liabilities related to net unrealized gains were $366 million and $323 million at March 31, 2019 and December 31, 2018, respectively. Accordingly, the fair value of trust assets available to pay future decommissioning costs, net of deferred income taxes, totaled $3.9 billion and $3.8 billion at March 31, 2019 and December 31, 2018, respectively. The following table summarizes the gains and (losses) for the trust investments:
| Three months ended March 31,
(in millions) | 2019 |  | 2018
Gross realized gains | $ | 23 |  |  | $ | 61 |
Gross realized loss | — |  |  | 8 |
Net unrealized gains (losses) for equity securities | $ | 168 |  |  | $ | (63 | )
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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