Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Debt Securities, Available-for-sale [Line Items]
Total	$ 2,055.0	$ 2,617.0
Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	10.0	3.0
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	74.0	197.0
Total	2,055.0	2,617.0
Entergy Arkansas [Member]
Debt Securities, Available-for-sale [Line Items]
Total	477.9	447.9
Entergy Arkansas [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	3.4	0.3
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	13.3	27.7
Total	477.9	447.9
Entergy Louisiana [Member]
Debt Securities, Available-for-sale [Line Items]
Total	705.8	632.2
Entergy Louisiana [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	3.3	0.5
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	33.1	51.3
Total	705.8	632.2
System Energy [Member]
Debt Securities, Available-for-sale [Line Items]
Total	468.0	427.7
System Energy [Member] | Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Available-for-sale, Unrealized Loss Position	2.4	0.8
Debt Securities, Available-for-sale, Accumulated Gross Unrealized Gain, before Tax	12.5	30.0
Total	$ 468.0	$ 427.7