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Decommissioning Trust Funds (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 | Jan. 01, 2018
Accumulated Other Comprehensive Income (Loss), Financial Liability, Fair Value Option, after Tax |  |  |  | $ (632,617)
Decommissioning Trust Funds [Abstract] |  |  |  |
Amortized cost of debt securities | $ 2,643,000 |  | $ 2,539,000 |
Average coupon rate of debt securities | 3.26% |  |  |
Average duration of debt securities, years | 6 years 66 days |  |  |
Average maturity of debt securities, years | 10 years 33 days |  |  |
Proceeds from the dispositions of debt securities | $ 1,091,000 | $ 514,000 |  |
Gains from dispositions of debt securities, gross | 1,000 | 9,000 |  |
Losses from dispositions of debt securities, gross | 7,000 | 5,000 |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  |  | (17,000) |
Equity Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts |  |  | 472,000 |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (64,000) |  | (1,000) |
Debt Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts | (2,000) |  | 7,000 |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (48,000) |  | (16,000) |
Entergy Arkansas [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Amortized cost of debt securities | $ 360,000 |  | 349,100 |
Average coupon rate of debt securities | 2.67% |  |  |
Average duration of debt securities, years | 5 years 175 days |  |  |
Average maturity of debt securities, years | 6 years 329 days |  |  |
Proceeds from the dispositions of debt securities | $ 34,900 | 36,000 |  |
Gains from dispositions of debt securities, gross | 100 | 500 |  |
Losses from dispositions of debt securities, gross | 0 | 100 |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  |  | (3,000) |
Entergy Arkansas [Member] | Equity Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (8,000) |  | 0 |
Entergy Arkansas [Member] | Debt Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (9,700) |  | (3,000) |
Entergy Louisiana [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Amortized cost of debt securities | $ 519,000 |  | 490,000 |
Average coupon rate of debt securities | 3.83% |  |  |
Average duration of debt securities, years | 6 years 18 days |  |  |
Average maturity of debt securities, years | 11 years 310 days |  |  |
Proceeds from the dispositions of debt securities | $ 125,500 | 40,600 |  |
Gains from dispositions of debt securities, gross | 500 | 0 |  |
Losses from dispositions of debt securities, gross | $ 800 | 200 |  |
Percentage Interest in River Bend | 30.00% |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  |  | (3,600) |
Entergy Louisiana [Member] | Equity Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $ (10,800) |  | 0 |
Entergy Louisiana [Member] | Debt Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (8,400) |  | (3,600) |
System Energy [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Amortized cost of debt securities | $ 330,000 |  | 327,500 |
Average coupon rate of debt securities | 2.72% |  |  |
Average duration of debt securities, years | 6 years 139 days |  |  |
Average maturity of debt securities, years | 9 years 141 days |  |  |
Proceeds from the dispositions of debt securities | $ 54,200 | 75,800 |  |
Gains from dispositions of debt securities, gross | 100 | 100 |  |
Losses from dispositions of debt securities, gross | 600 | $ 700 |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  |  | (1,200) |
System Energy [Member] | Equity Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (7,800) |  | 0 |
System Energy [Member] | Debt Securities [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | (5,800) |  | (1,200) |
Indian Point 3 [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Decommissioning Fund Investments, Fair Value | 789,000 |  | 798,000 |
Indian Point 1 [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Decommissioning Fund Investments, Fair Value | 485,000 |  | 491,000 |
Indian Point 2 [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Decommissioning Fund Investments, Fair Value | 614,000 |  | 621,000 |
Palisades [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Decommissioning Fund Investments, Fair Value | 453,000 |  | 458,000 |
Pilgrim [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Decommissioning Fund Investments, Fair Value | 1,048,000 |  | 1,068,000 |
Vermont Yankee [Member] |  |  |  |
Decommissioning Trust Funds [Abstract] |  |  |  |
Decommissioning Fund Investments, Fair Value | $ 591,000 |  | $ 613,000 |

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