Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 5,671.0	$ 5,350.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,662.0	1,437.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3.0	19.0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	3,380.0	3,195.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,568.0	1,396.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1.0	2.0
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,291.0	2,155.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	94.0	41.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2.0	17.0
Entergy Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	823.8	771.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	274.2	238.5
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.3	2.4
Entergy Arkansas [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	504.9	467.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	263.4	234.4
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	0.2
Entergy Arkansas [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	318.9	303.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	10.8	4.1
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.3	2.2
Entergy Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,124.8	1,042.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	344.3	296.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.4	2.6
Entergy Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	684.7	632.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	322.9	283.7
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	0.2
Entergy Louisiana [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	440.1	409.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	21.4	13.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.4	2.4
System Energy [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	764.9	701.5
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	212.2	181.4
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.4	2.6
System Energy [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	456.3	423.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	205.5	179.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.1	0.3
System Energy [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	308.6	277.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	6.7	2.2
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 0.3	$ 2.3