Decommissioning Trust Funds (Fair Value Of Debt Securities By Contractual Maturities) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Fair value of debt securities by contractual maturities
less than 1 year	$ 125.0	$ 77.0
1 year - 5 years	763.0	857.0
5 years - 10 years	719.0	704.0
10 years - 15 years	109.0	124.0
15 years - 20 years	73.0	50.0
20 years	424.0	343.0
Total	2,213.0	2,155.0
Entergy Arkansas [Member]
Fair value of debt securities by contractual maturities
less than 1 year	16.7	1.8
1 year - 5 years	106.2	145.2
5 years - 10 years	161.2	138.5
10 years - 15 years	7.7	2.4
15 years - 20 years	1.0	2.0
20 years	16.5	14.0
Total	309.3	303.9
Entergy Louisiana [Member]
Fair value of debt securities by contractual maturities
less than 1 year	31.4	27.1
1 year - 5 years	99.1	124.0
5 years - 10 years	122.8	114.3
10 years - 15 years	41.4	39.3
15 years - 20 years	30.9	26.5
20 years	99.2	78.7
Total	424.8	409.9
System Energy [Member]
Fair value of debt securities by contractual maturities
less than 1 year	6.6	2.0
1 year - 5 years	188.2	181.2
5 years - 10 years	78.5	63.0
10 years - 15 years	1.3	4.4
15 years - 20 years	7.8	1.6
20 years	24.2	25.6
Total	$ 306.6	$ 277.8