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Investments | 3 Months Ended
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Mar. 31, 2016
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, 2016 |  | December 31, 2015 |  | March 31, 2016 |  | December 31, 2015
Stocks | — |  | $ | 311 |  |  | $ | 304 |  |  | $ | 1,464 |  |  | $ | 1,460 |
Municipal bonds | 2054 |  | 736 |  |  | 691 |  |  | 894 |  |  | 840 |
U.S. government and agency securities | 2046 |  | 1,002 |  |  | 1,070 |  |  | 1,092 |  |  | 1,128 |
Corporate bonds | 2057 |  | 662 |  |  | 708 |  |  | 731 |  |  | 755 |
Short-term investments and receivables/payables 1 | One-year |  | 106 |  |  | 144 |  |  | 109 |  |  | 148 |
Total |  |  | $ | 2,817 |  |  | $ | 2,917 |  |  | $ | 4,290 |  |  | $ | 4,331 |
1 | Short-term investments include $8 million and $81 million of repurchase agreements payable by financial institutions which earn interest, are fully secured by U.S. Treasury securities and mature by April 4, 2016 and January 5, 2016 as of March 31, 2016 and December 31, 2015, 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 $1.5 billion and $1.4 billion at March 31, 2016 and December 31, 2015, respectively. The following table sets forth a summary of changes in the fair value of the trust:
|  | Three months ended March 31,
(in millions) |  | 2016 |  | 2015
Balance at beginning of period |  | $ | 4,331 |  |  | $ | 4,799 |
Gross realized gains |  | 17 |  |  | 27 |
Gross realized losses |  | (3 | ) |  | (2 | )
Unrealized gains, net |  | 59 |  |  | 44 |
Other-than-temporary impairments |  | (7 | ) |  | (4 | )
Interest and dividends |  | 29 |  |  | 28 |
Contributions |  | — |  |  | 7 |
Income taxes |  | (18 | ) |  | — |
Decommissioning disbursements |  | (116 | ) |  | — |
Administrative expenses and other |  | (2 | ) |  | (3 | )
Balance at end of period |  | $ | 4,290 |  |  | $ | 4,896 |
Trust assets are used to pay income taxes as the Trust files separate income taxes returns from SCE. Deferred income taxes related to unrealized gains at March 31, 2016 were $357 million. Accordingly, the fair value of Trust assets available to pay future decommissioning costs, net of deferred income taxes, totaled $3.9 billion at March 31, 2016. 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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