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Investments | 3 Months Ended
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Mar. 31, 2021
Regulated Entity, Other Assets, Noncurrent [Abstract] |
Investments | Note 10.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): ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | ​ | ​ | Amortized Cost | ​ | Fair Value
​ | ​ | Longest | ​ | March 31, | ​ | December 31, | ​ | March 31, | ​ | December 31,
(in millions) |  | Maturity Dates |  | 2021 |  | 2020 |  | 2021 |  | 2020
Stocks |  | — |  | ​ | N/A |  | ​ | N/A | ​ | $ | 1,896 | ​ | $ | 1,908
Municipal bonds |  | 2054 |  | $ | 1,044 |  | $ | 1,013 | ​ |  | 1,212 | ​ |  | 1,218
U.S. government and agency securities |  | 2067 |  | ​ | 683 |  | ​ | 740 | ​ |  | 754 | ​ |  | 864
Corporate bonds |  | 2070 |  | ​ | 451 |  | ​ | 460 | ​ |  | 519 | ​ |  | 550
Short-term investments and receivables/payables1 |  | One-year |  | ​ | 366 |  | ​ | 281 | ​ |  | 382 | ​ |  | 293
Total |  |  | ​ | $ | 2,544 | ​ | $ | 2,494 | ​ | $ | 4,763 | ​ | $ | 4,833
1 | Short-term investments include $144 million and $138 million of repurchase agreements payable by financial institutions which earn interest, are fully secured by U.S. Treasury securities and mature by April 1, 2021 and January 4, 2021 as of March 31, 2021 and December 31, 2020, 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 $2.0 billion and $2.1 billion at March 31, 2021 and December 31, 2020, respectively. Trust assets are used to pay income taxes arising from trust investing activity. Deferred tax liabilities related to net unrealized gains were $477 million and $515 million at March 31, 2021 and December 31, 2020, respectively. Accordingly, the fair value of trust assets available to pay future decommissioning costs, net of deferred income taxes, totaled $4.3 billion at both March 31, 2021 and December 31, 2020. The following table summarizes the gains and losses for the trust investments: ​
​ | ​ | ​ | ​ | ​ | ​ | ​ | ​
​ | ​ | Three months ended March 31, | ​
(in millions) |  | 2021 |  | 2020 | ​
Gross realized gains | ​ | $ | 111 | ​ | $ | 39 | ​
Gross realized loss | ​ |  | 12 | ​ |  | 2 | ​
Net unrealized gains (losses) for equity securities | ​ |  | 18 | ​ |  | (376) | ​
​ 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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