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Investments | 3 Months Ended
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Mar. 31, 2017
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, 2017 |  | December 31, 2016 |  | March 31, 2017 |  | December 31, 2016
Stocks | — |  | $ | 291 |  |  | $ | 319 |  |  | $ | 1,537 |  |  | $ | 1,547 |
Municipal bonds | 2054 |  | 645 |  |  | 659 |  |  | 753 |  |  | 766 |
U.S. government and agency securities | 2055 |  | 1,308 |  |  | 1,131 |  |  | 1,380 |  |  | 1,191 |
Corporate bonds | 2057 |  | 552 |  |  | 600 |  |  | 608 |  |  | 659 |
Short-term investments and receivables/payables 1 | One-year |  | 71 |  |  | 75 |  |  | 74 |  |  | 79 |
Total |  |  | $ | 2,867 |  |  | $ | 2,784 |  |  | $ | 4,352 |  |  | $ | 4,242 |
1 | Short-term investments include $36 million and $114 million of repurchase agreements payable by financial institutions which earn interest, are fully secured by U.S. Treasury securities and mature by April 3, 2017 and J anuary 4, 2017 as of March 31, 2017 and December 31, 2016, 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 $1.5 billion at both March 31, 2017 and December 31, 2016. The following table sets forth a summary of changes in the fair value of the trust:
|  | Three months ended March 31,
(in millions) |  | 2017 |  | 2016
Balance at beginning of period |  | $ | 4,242 |  |  | $ | 4,331 |
Gross realized gains |  | 99 |  |  | 17 |
Gross realized losses |  | (16 | ) |  | (3 | )
Unrealized gains, net of losses |  | 27 |  |  | 59 |
Other-than-temporary impairments |  | (1 | ) |  | (7 | )
Interest and dividends |  | 28 |  |  | 29 |
Income taxes |  | — |  |  | (18 | )
Decommissioning disbursements |  | (26 | ) |  | (116 | )
Administrative expenses and other |  | (1 | ) |  | (2 | )
Balance at end of period |  | $ | 4,352 |  |  | $ | 4,290 |
Trust assets are used to pay income taxes. Deferred tax liabilities related to net unrealized gains at March 31, 2017 were $373 million. Accordingly, the fair value of trust assets available to pay future decommissioning costs, net of deferred income taxes, totaled $4.0 billion at March 31, 2017. Due to regulatory mechanisms, changes in assets of the trusts from income or loss items have no impact on operating revenue or earnings. Decommissioning disbursements are funded from sales of investments of the nuclear decommissioning trusts.

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