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Decommissioning Trust Funds (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2016 | Mar. 31, 2015 | Dec. 31, 2015
Decommissioning Trust Funds [Abstract] |  |  |
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts | $ 361,000 |  | $ 342,000
Amortized cost of debt securities | $ 2,183,000 |  | 2,124,000
Average coupon rate of debt securities | 3.20% |  |
Average duration of debt securities, years | 5 years 10 months 2 days |  |
Average maturity of debt securities, years | 8 years 10 months 28 days |  |
Proceeds from the dispositions of debt securities | $ 729,000 | $ 493,000 |
Gains from dispositions of debt securities, gross | 10,000 | 26,000 |
Losses from dispositions of debt securities, gross | 3,000 | 2,000 |
Entergy Arkansas [Member] |  |  |
Decommissioning Trust Funds [Abstract] |  |  |
Amortized cost of debt securities | $ 302,000 |  | 301,800
Average coupon rate of debt securities | 2.58% |  |
Average duration of debt securities, years | 5 years 3 months |  |
Average maturity of debt securities, years | 6 years 1 month 28 days |  |
Proceeds from the dispositions of debt securities | $ 58,600 | 81,900 |
Gains from dispositions of debt securities, gross | 800 | 5,100 |
Losses from dispositions of debt securities, gross | $ 100 | 0 |
Entergy Louisiana [Member] |  |  |
Decommissioning Trust Funds [Abstract] |  |  |
Percentage Interest in River Bend | 30.00% |  |
Amortized cost of debt securities | $ 407,000 |  | 399,200
Average coupon rate of debt securities | 3.89% |  |
Average duration of debt securities, years | 5 years 6 months 16 days |  |
Average maturity of debt securities, years | 10 years 2 months 28 days |  |
Proceeds from the dispositions of debt securities | $ 53,800 | 25,600 |
Gains from dispositions of debt securities, gross | 900 | 1,300 |
Losses from dispositions of debt securities, gross | 100 | 10 |
System Energy [Member] |  |  |
Decommissioning Trust Funds [Abstract] |  |  |
Amortized cost of debt securities | $ 286,900 |  | $ 270,700
Average coupon rate of debt securities | 1.93% |  |
Average duration of debt securities, years | 5 years 7 days |  |
Average maturity of debt securities, years | 6 years 4 months 14 days |  |
Proceeds from the dispositions of debt securities | $ 188,500 | 78,400 |
Gains from dispositions of debt securities, gross | 1,600 | 400 |
Losses from dispositions of debt securities, gross | $ 300 | $ 100 |

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