Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 7,212.0	$ 5,724.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,175.0	1,707.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	17.0	28.0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	4,662.0	3,511.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,131.0	1,673.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1.0	1.0
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,550.0	2,213.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	44.0	34.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	16.0	27.0
Entergy Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,312.1	1,140.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	472.1	354.6
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3.6	5.0
Entergy Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	818.3	715.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	461.2	346.6
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Entergy Louisiana [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	493.8	424.8
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	10.9	8.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3.6	5.0
Entergy Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	944.9	834.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	357.0	284.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3.0	4.2
Entergy Arkansas [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	596.7	525.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	354.9	281.5
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	0.0
Entergy Arkansas [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	348.2	309.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2.1	3.4
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	3.0	4.2
System Energy [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	905.7	780.5
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	312.8	223.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1.2	4.6
System Energy [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	575.2	473.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	308.6	221.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	0.1
System Energy [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	330.5	306.6
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	4.2	2.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 1.2	$ 4.5