Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Total	$ 2,617.0	$ 2,456.0
Debt Securities, Trading	507.0
Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	2,617.0	2,456.0
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	197.0	96.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3.0	6.0
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Total	632.2	601.5
Entergy Louisiana [Member] \| Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	632.2	601.5
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	51.3	29.3
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.5	0.8
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Total	447.9	412.8
Entergy Arkansas [Member] \| Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	447.9	412.8
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	27.7	9.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.3	2.6
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Total	427.7	386.2
System Energy [Member] \| Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Fair Value	427.7	386.2
Available-for-sale Equity Securities, Accumulated Gross Unrealized Gain, before Tax	30.0	15.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0.8	$ 0.3

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