Decommissioning Trust Funds (Fair Value Of Debt Securities By Contractual Maturities) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Fair value of debt securities by contractual maturities
less than 1 year	$ 74.0	$ 125.0
1 year - 5 years	902.0	763.0
5 years - 10 years	812.0	719.0
10 years - 15 years	147.0	109.0
15 years - 20 years	100.0	73.0
20 years	515.0	424.0
Total	2,550.0	2,213.0
Entergy Arkansas [Member]
Fair value of debt securities by contractual maturities
less than 1 year	13.0	16.7
1 year - 5 years	123.4	106.2
5 years - 10 years	180.6	161.2
10 years - 15 years	4.8	7.7
15 years - 20 years	3.4	1.0
20 years	23.0	16.5
Total	348.2	309.3
Entergy Louisiana [Member]
Fair value of debt securities by contractual maturities
less than 1 year	23.2	31.4
1 year - 5 years	122.8	99.1
5 years - 10 years	109.3	122.8
10 years - 15 years	52.7	41.4
15 years - 20 years	50.7	30.9
20 years	135.1	99.2
Total	493.8	424.8
System Energy [Member]
Fair value of debt securities by contractual maturities
less than 1 year	4.1	6.6
1 year - 5 years	173.0	188.2
5 years - 10 years	78.5	78.5
10 years - 15 years	1.0	1.3
15 years - 20 years	6.9	7.8
20 years	67.0	24.2
Total	$ 330.5	$ 306.6