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Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
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Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value |  | $ 8.0
More than 12 months Fair Value |  | 0.0
Total Fair Value |  | 8.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 1.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 1.0
Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value | $ 1,667.0 | 1,099.0
More than 12 months Fair Value | 241.0 | 265.0
Total Fair Value | 1,908.0 | 1,364.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 35.0 | 7.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 13.0 | 9.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | 48.0 | 16.0
Entergy Arkansas [Member] | Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value |  | 0.0
More than 12 months Fair Value |  | 0.0
Total Fair Value |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 0.0
Entergy Arkansas [Member] | Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value | 277.8 | 168.0
More than 12 months Fair Value | 42.5 | 41.4
Total Fair Value | 320.3 | 209.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 7.2 | 1.2
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 2.5 | 1.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | 9.7 | 3.0
Entergy Louisiana [Member] | Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value |  | 0.0
More than 12 months Fair Value |  | 0.0
Total Fair Value |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 0.0
Entergy Louisiana [Member] | Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value | 254.9 | 135.3
More than 12 months Fair Value | 78.8 | 84.4
Total Fair Value | 333.7 | 219.7
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 4.6 | 1.1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 3.8 | 2.5
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | 8.4 | 3.6
System Energy [Member] | Equity Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value |  | 0.0
More than 12 months Fair Value |  | 0.0
Total Fair Value |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss |  | 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss |  | 0.0
System Energy [Member] | Debt Securities [Member] |  |
Schedule of Available-for-sale Securities [Line Items] |  |
Less than 12 months Fair Value | 240.7 | 196.9
More than 12 months Fair Value | 10.2 | 10.4
Total Fair Value | 250.9 | 207.3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss | 5.5 | 1.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss | 0.3 | 0.2
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss | $ 5.8 | $ 1.2

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- Definition Amount of accumulated unrealized loss on investments in debt and equity securities classified as available-for-sale that have been in a continuous loss position for twelve months or longer. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 6 -Subparagraph (a)(2) -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27290-111563 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 50 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=82897076&loc=d3e27337-111563 + Details
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