Decommissioning Trust Funds (Securities Held) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 6,983.0	$ 5,724.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	2,028.0	1,707.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	14.0	28.0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	4,554.0	3,511.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	1,983.0	1,673.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	0.0	1.0
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,429.0	2,213.0
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	45.0	34.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	14.0	27.0
Entergy Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	910.4	834.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	330.3	284.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2.3	4.2
Entergy Arkansas [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	576.3	525.4
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	327.2	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	334.1	309.3
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	3.1	3.4
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2.3	4.2
Entergy Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,260.0	1,140.7
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	431.2	354.6
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	2.8	5.0
Entergy Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	781.2	715.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	420.3	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	478.8	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	2.8	5.0
System Energy [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	870.6	780.5
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	279.9	223.9
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	1.9	4.6
System Energy [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	541.0	473.9
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	276.2	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	329.6	306.6
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax	3.7	2.0
Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax	$ 1.9	$ 4.5