Decommissioning Trust Funds (Fair Value Of Debt Securities By Contractual Maturities) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair value of debt securities by contractual maturities
Less than 1 year	$ 91.0	$ 125.0
1 year - 5 years	801.0	763.0
5 years - 10 years	789.0	719.0
10 years - 15 years	130.0	109.0
15 years - 20 years	87.0	73.0
20 years+	531.0	424.0
Total	2,429.0	2,213.0
Entergy Arkansas [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	11.8	16.7
1 year - 5 years	107.9	106.2
5 years - 10 years	194.4	161.2
10 years - 15 years	2.6	7.7
15 years - 20 years	1.4	1.0
20 years+	16.0	16.5
Total	334.1	309.3
Entergy Louisiana [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	27.7	31.4
1 year - 5 years	113.2	99.1
5 years - 10 years	117.1	122.8
10 years - 15 years	50.7	41.4
15 years - 20 years	43.4	30.9
20 years+	126.7	99.2
Total	478.8	424.8
System Energy [Member]
Fair value of debt securities by contractual maturities
Less than 1 year	8.7	6.6
1 year - 5 years	170.7	188.2
5 years - 10 years	79.1	78.5
10 years - 15 years	4.4	1.3
15 years - 20 years	6.5	7.8
20 years+	60.2	24.2
Total	$ 329.6	$ 306.6