Decommissioning Trust Funds (Fair Value Of Debt Securities By Contractual Maturities) (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Fair value of debt securities by contractual maturities
Less than 1 year	$ 24.0	$ 128.0
1 year - 5 years	718.0	807.0
5 years - 10 years	761.0	666.0
10 years - 15 years	347.0	125.0
15 years - 20 years	135.0	126.0
20 years+	596.0	604.0
Total	2,581.0	2,456.0
Entergy Arkansas [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	13.6	44.1
1 year - 5 years	102.0	109.1
5 years - 10 years	177.5	156.0
10 years - 15 years	75.8	31.3
15 years - 20 years	26.7	23.8
20 years+	37.6	48.5
Total	433.2	412.8
Entergy Louisiana [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	7.7	40.7
1 year - 5 years	122.9	142.0
5 years - 10 years	147.8	132.4
10 years - 15 years	95.1	39.8
15 years - 20 years	61.8	49.2
20 years+	191.1	197.4
Total	626.4	601.5
System Energy [Member]
Fair value of debt securities by contractual maturities
Less than 1 year		8.5
1 year - 5 years	163.1	154.6
5 years - 10 years	107.0	92.3
10 years - 15 years	27.5	13.4
15 years - 20 years	4.9	14.4
20 years+	119.9	103.0
Total	420.8	$ 386.2
Debt Securities, Available-for-Sale, Maturity, Allocated and Single Maturity Date, within One Year, Negative Fair Value	$ (1.6)