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Retirement And Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Thousands | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Mar. 31, 2018 | Mar. 31, 2017 | Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | $ 21,000 | $ 108,000 | $ 71,000 | $ 148,000 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | $ 91,800 |  |  |  |  |
Entergy Arkansas [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | 2,800 | 13,700 | 13,400 | 30,700 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 17,373 |  |  |  |  |
Entergy Louisiana [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | 6,100 | 27,800 | 26,100 | 50,700 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 19,510 |  |  |  |  |
Entergy Mississippi [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | 600 | 2,700 | 2,400 | 6,300 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 4,194 |  |  |  |  |
Entergy New Orleans [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | 200 | 1,300 | 1,000 | 4,000 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 2,061 |  |  |  |  |
Entergy Texas [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | (200) | 200 | (1,100) | 4,000 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 3,873 |  |  |  |  |
System Energy [Member] |  |  |  |  |  |
Defined Benefit Plan Disclosure [Line Items] |  |  |  |  |  |
New Accounting Pronouncement or Change in Accounting Principle, Effect of Change on Operating Results |  | 900 | $ 6,200 | $ 5,100 | $ 10,200 |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Plan Assets, Contributions by Employer | 3,715 |  |  |  |  |
Subsequent Event [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | $ 352,100
Subsequent Event [Member] | Entergy Arkansas [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | 64,062
Defined Benefit Plan Remaining Contributions To Be Made In Current Fiscal Year |  |  |  |  |  | 46,689
Subsequent Event [Member] | Entergy Louisiana [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | 71,917
Defined Benefit Plan Remaining Contributions To Be Made In Current Fiscal Year |  |  |  |  |  | 52,407
Subsequent Event [Member] | Entergy Mississippi [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | 14,933
Defined Benefit Plan Remaining Contributions To Be Made In Current Fiscal Year |  |  |  |  |  | 10,739
Subsequent Event [Member] | Entergy New Orleans [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | 7,250
Defined Benefit Plan Remaining Contributions To Be Made In Current Fiscal Year |  |  |  |  |  | 5,189
Subsequent Event [Member] | Entergy Texas [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | 10,883
Defined Benefit Plan Remaining Contributions To Be Made In Current Fiscal Year |  |  |  |  |  | 7,010
Subsequent Event [Member] | System Energy [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Defined Benefit Plan, Expected Future Employer Contributions, Remainder of Fiscal Year |  |  |  |  |  | 13,786
Defined Benefit Plan Remaining Contributions To Be Made In Current Fiscal Year |  |  |  |  |  | $ 10,071
Non Qualified Pension Plans [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Net periodic benefit costs | 8,900 | 4,600 |  |  |  |
Settlement Charge Associated With Out Of Plan Payment Of Lump Sum Benefits | 4,400 |  |  |  |  |
Non Qualified Pension Plans [Member] | Entergy Arkansas [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Net periodic benefit costs | 132 | 105 |  |  |  |
Settlement Charge Associated With Out Of Plan Payment Of Lump Sum Benefits | 12 |  |  |  |  |
Non Qualified Pension Plans [Member] | Entergy Louisiana [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Net periodic benefit costs | 50 | 48 |  |  |  |
Non Qualified Pension Plans [Member] | Entergy Mississippi [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Net periodic benefit costs | 80 | 64 |  |  |  |
Non Qualified Pension Plans [Member] | Entergy New Orleans [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Net periodic benefit costs | 21 | 18 |  |  |  |
Non Qualified Pension Plans [Member] | Entergy Texas [Member] |  |  |  |  |  |
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |  |  |  |  |  |
Net periodic benefit costs | $ 137 | $ 127 |  |  |  |

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