Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) - Debt Securities [Member] - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	$ 650.0	$ 187.0
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	35.0	2.0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	685.0	189.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	9.0	3.0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	1.0	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	10.0	3.0
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	171.1	29.9
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	17.5	0.0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	188.6	29.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2.6	0.3
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.8	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	3.4	0.3
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	173.2	36.4
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	15.0	0.8
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	188.2	37.2
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2.6	0.5
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.7	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	3.3	0.5
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, Less than 12 Months, Fair Value	200.6	28.9
Debt Securities, Held-to-maturity, Continuous Unrealized Loss Position, 12 Months or Longer, Fair Value	1.4	0.0
Debt Securities, Held-to-maturity, Unrealized Loss Position, Fair Value	202.0	28.9
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	2.4	0.8
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0.0	0.0
Debt Securities, Available-for-sale, Unrealized Loss Position	$ 2.4	$ 0.8

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

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Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

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