Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 189.0	$ 442.0
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	3.0	6.0
Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	2.0	38.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	187.0	404.0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3.0	5.0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	1.0
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	29.9	112.5
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.3	2.6
Entergy Arkansas [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0.0	7.7
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	29.9	104.8
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.3	2.5
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0.0	0.1
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	37.2	79.1
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.5	0.8
Entergy Louisiana [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0.8	7.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	36.4	71.2
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
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	28.9	57.2
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	0.8	0.3
System Energy [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0.0	0.3
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	28.9	56.9
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0.8	0.3
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	$ 0.0	$ 0.0