Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	$ 404.0	$ 652.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5.0	9.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	38.0	782.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1.0	26.0
Debt Securities, Available-for-sale, Unrealized Loss Position	442.0	1,434.0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6.0	35.0
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	104.8	65.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2.5	0.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	7.7	231.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.1	7.7
Debt Securities, Available-for-sale, Unrealized Loss Position	112.5	296.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	2.6	8.2
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	71.2	170.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.8	2.1
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	7.9	145.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	3.9
Debt Securities, Available-for-sale, Unrealized Loss Position	79.1	315.9
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.8	6.0
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	56.9	89.7
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.3	2.4
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.3	79.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	3.4
Debt Securities, Available-for-sale, Unrealized Loss Position	57.2	169.5
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 0.3	$ 5.8