Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Total	$ 2,456.0	$ 2,495.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	96.0	19.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	6.0	35.0
Debt Securities, Trading	507.0	389.0
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Total	601.5	532.9
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	29.3	4.1
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	0.8	6.0
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Total	412.8	381.3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	9.9	0.6
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	2.6	8.2
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Total	386.2	364.2
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	15.1	2.9
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Loss, before Tax	$ 0.3	$ 5.8