The following table shows the fair values and gross unrealized gains and losses for the securities held in the NDT. We provide additional fair value disclosures for the NDT in Note 8. | | | | | | | | | | | | | | | | | NUCLEAR DECOMMISSIONING TRUSTS | (Dollars in millions) | | Cost | | Gross unrealized gains | | Gross unrealized losses | | Estimated fair value | At September 30, 2016: | | | | | | | | Debt securities: | | | | | | | | Debt securities issued by the U.S. Treasury and other | | | | | | | | U.S. government corporations and agencies(1) | $ | 95 |
| | $ | 5 |
| | $ | — |
| | $ | 100 |
| Municipal bonds(2) | 150 |
| | 11 |
| | — |
| | 161 |
| Other securities(2) | 183 |
| | 9 |
| | (4 | ) | | 188 |
| Total debt securities | 428 |
| | 25 |
| | (4 | ) | | 449 |
| Equity securities | 188 |
| | 422 |
| | (3 | ) | | 607 |
| Cash and cash equivalents | 12 |
| | — |
| | — |
| | 12 |
| Total | $ | 628 |
| | $ | 447 |
| | $ | (7 | ) | | $ | 1,068 |
| At December 31, 2015: | | | | | | | | Debt securities: | | | | | | | | Debt securities issued by the U.S. Treasury and other | | | | | | | | U.S. government corporations and agencies | $ | 89 |
| | $ | 2 |
| | $ | — |
| | $ | 91 |
| Municipal bonds | 148 |
| | 8 |
| | — |
| | 156 |
| Other securities | 194 |
| | 1 |
| | (13 | ) | | 182 |
| Total debt securities | 431 |
| | 11 |
| | (13 | ) | | 429 |
| Equity securities | 214 |
| | 412 |
| | (7 | ) | | 619 |
| Cash and cash equivalents | 15 |
| | — |
| | — |
| | 15 |
| Total | $ | 660 |
| | $ | 423 |
| | $ | (20 | ) | | $ | 1,063 |
|
| | (1) | Maturity dates are 2017-2065. |
| | (2) | Maturity dates are 2016-2115. |
|