Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - Debt Securities [Member] - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	$ 411.0	$ 404.0
More than 12 months Fair Value	5.0	38.0
Total Fair Value	416.0	442.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	16.0	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	16.0	6.0
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	60.2	104.8
More than 12 months Fair Value	0.0	7.7
Total Fair Value	60.2	112.5
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1.4	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	1.4	2.6
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	95.2	71.2
More than 12 months Fair Value	0.8	7.9
Total Fair Value	96.0	79.1
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3.9	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	3.9	0.8
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Less than 12 months Fair Value	52.3	56.9
More than 12 months Fair Value	0.0	0.3
Total Fair Value	52.3	57.2
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2.7	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	$ 2.7	$ 0.3