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Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | $ 7,212.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 2,175.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | 17.0
Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 4,662.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 2,131.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $ 64.0 | 1.0
Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value | 2,619.0 | 2,550.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 23.0 | 44.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 48.0 | 16.0
Entergy Arkansas [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 944.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 357.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | 3.0
Entergy Arkansas [Member] | Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 596.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 354.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 8.0 | 0.0
Entergy Arkansas [Member] | Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value | 350.8 | 348.2
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 0.5 | 2.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 9.7 | 3.0
Entergy Louisiana [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 1,312.1
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 472.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | 3.6
Entergy Louisiana [Member] | Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 818.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 461.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 10.8 | 0.0
Entergy Louisiana [Member] | Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value | 516.3 | 493.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 5.7 | 10.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 8.4 | 3.6
System Energy [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 905.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 312.8
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax |  | 1.2
System Energy [Member] | Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value |  | 575.2
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax |  | 308.6
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | 7.8 | 0.0
System Energy [Member] | Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Fair Value | 325.6 | 330.5
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax | 1.4 | 4.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax | $ 5.8 | $ 1.2

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