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Other Investments | 3 Months Ended
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Mar. 31, 2013
Regulated Entity, Other Assets, Noncurrent [Abstract] |
Other Investments | Other Investments Nuclear Decommissioning Trusts Future decommissioning costs of removal of SCE's nuclear assets are expected to be funded from independent decommissioning trusts, which currently receive contributions of approximately $23 million per year through SCE customer rates. Contributions to the decommissioning trusts are reviewed every three years by the CPUC. During 2012, SCE filed with the CPUC a nuclear decommissioning cost application which includes the 2011 San Onofre and 2010 Palo Verde site-specific decommissioning studies. If the CPUC approves the studies, the annual trust contributions are expected to increase to $41 million in 2014. If additional funds are needed for decommissioning, it is probable that the additional funds will be recoverable through customer rates. Funds collected, together with accumulated earnings, will be utilized solely for decommissioning. The CPUC has set certain restrictions related to the investments of these trusts. The following table sets forth amortized cost and fair value of the trust investments:
| Longest Maturity Dates |  | Amortized Cost |  | Fair Value
(in millions) |  | March 31, 2013 |  | December 31, 2012 |  | March 31, 2013 |  | December 31, 2012
Stocks | — |  | $ | 990 |  |  | $ | 978 |  |  | $ | 2,468 |  |  | $ | 2,271 |
Municipal bonds | 2051 |  | 509 |  |  | 518 |  |  | 631 |  |  | 644 |
U.S. government and agency securities | 2043 |  | 590 |  |  | 547 |  |  | 646 |  |  | 603 |
Corporate bonds | 2054 |  | 327 |  |  | 324 |  |  | 408 |  |  | 410 |
Short-term investments and receivables/payables | One-year |  | 89 |  |  | 116 |  |  | 93 |  |  | 120 |
Total |  |  | $ | 2,505 |  |  | $ | 2,483 |  |  | $ | 4,246 |  |  | $ | 4,048 |
Trust fund earnings (based on specific identification) increase the trust fund balance and the ARO regulatory liability. Proceeds from sales of securities (which are reinvested) were $435 million and $602 million for the three months ended March 31, 2013 and 2012, respectively. Unrealized holding gains, net of losses, were $1.7 billion and $1.6 billion at March 31, 2013 and December 31, 2012, respectively. The following table sets forth a summary of changes in the fair value of the trust:
| Three months ended March 31,
(in millions) | 2013 |  | 2012
Balance at beginning of period | $ | 4,048 |  |  | $ | 3,592 |
Gross realized gains | 5 |  |  | 25 |
Gross realized losses | (1 | ) |  | (4 | )
Unrealized gains, net | 176 |  |  | 184 |
Other-than-temporary impairments | (8 | ) |  | (5 | )
Interest, dividends, contributions and other | 26 |  |  | 61 |
Balance at end of period | $ | 4,246 |  |  | $ | 3,853 |
Due to regulatory mechanisms, earnings and realized gains and losses (including other-than-temporary impairments) have no impact on operating revenue or earnings.

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- Definition This element represents the disclosure of other investments held by the entity for investment purposes not otherwise defined in the taxonomy. + References No definition available. + Details
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