Decommissioning Trust Funds (Fair Value Of Debt Securities By Contractual Maturities) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair value of debt securities by contractual maturities
Less than 1 year	$ 89.0	$ 74.0
1 year - 5 years	928.0	902.0
5 years - 10 years	784.0	812.0
10 years - 15 years	152.0	147.0
15 years - 20 years	101.0	100.0
20 years+	565.0	515.0
Total	2,619.0	2,550.0
Entergy Arkansas [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	14.1	13.0
1 year - 5 years	130.6	123.4
5 years - 10 years	177.9	180.6
10 years - 15 years	3.4	4.8
15 years - 20 years	7.0	3.4
20 years+	17.8	23.0
Total	350.8	348.2
Entergy Louisiana [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	28.1	23.2
1 year - 5 years	136.7	122.8
5 years - 10 years	108.4	109.3
10 years - 15 years	52.9	52.7
15 years - 20 years	44.7	50.7
20 years+	145.5	135.1
Total	516.3	493.8
System Energy [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	5.5	4.1
1 year - 5 years	164.5	173.0
5 years - 10 years	78.4	78.5
10 years - 15 years	3.8	1.0
15 years - 20 years	10.7	6.9
20 years+	62.7	67.0
Total	$ 325.6	$ 330.5