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Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - Debt Securities [Member] - USD ($)
$ in Millions
Sep. 30, 2020
Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value $ 206.0 $ 404.0
More than 12 months Fair Value 2.0 38.0
Total Fair Value 208.0 442.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 2.0 5.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 0.0 1.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 2.0 6.0
Entergy Arkansas [Member]    
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value 26.8 104.8
More than 12 months Fair Value 0.0 7.7
Total Fair Value 26.8 112.5
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.2 2.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 0.0 0.1
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 0.2 2.6
Entergy Louisiana [Member]    
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value 43.7 71.2
More than 12 months Fair Value 0.8 7.9
Total Fair Value 44.5 79.1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.5 0.8
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 0.0 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss 0.5 0.8
System Energy [Member]    
Debt Securities, Available-for-sale [Line Items]    
Less than 12 months Fair Value 28.7 56.9
More than 12 months Fair Value 0.0 0.3
Total Fair Value 28.7 57.2
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss 0.4 0.3
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss 0.0 0.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss $ 0.4 $ 0.3