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Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - Debt Securities [Member] - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value $ 197.0 $ 652.0
More than 12 months Fair Value 588.0 782.0
Total Fair Value 785.0 1,434.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 1.0 9.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 8.0 26.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 9.0 35.0
Entergy Arkansas [Member]    
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value 3.6 65.8
More than 12 months Fair Value 182.7 231.1
Total Fair Value 186.3 296.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.0 0.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 2.3 7.7
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 2.3 8.2
Entergy Louisiana [Member]    
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value 26.5 170.1
More than 12 months Fair Value 87.4 145.8
Total Fair Value 113.9 315.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.2 2.1
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 1.2 3.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 1.4 6.0
System Energy [Member]    
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value 44.2 89.7
More than 12 months Fair Value 77.4 79.8
Total Fair Value 121.6 169.5
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.0 2.4
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 1.2 3.4
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ 1.2 $ 5.8