Decommissioning Trust Funds (Securities Held) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 4,190.0	$ 3,788.0
Total Unrealized Gains	778.0	538.0
Total Unrealized Losses	6.0	19.0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,459.0	2,129.0
Total Unrealized Gains	662.0	423.0
Total Unrealized Losses	1.0	14.0
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,731.0	1,659.0
Total Unrealized Gains	116.0	115.0
Total Unrealized Losses	5.0	5.0
Entergy Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	600.6	541.7
Total Unrealized Gains	130.6	86.1
Total Unrealized Losses	0.2	0.8
Entergy Arkansas [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	384.0	329.4
Total Unrealized Gains	116.1	70.9
Total Unrealized Losses		0.4
Entergy Arkansas [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	216.6	212.3
Total Unrealized Gains	14.5	15.2
Total Unrealized Losses	0.2	0.4
Entergy Gulf States Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	477.4	420.9
Total Unrealized Gains	85.6	56.1
Total Unrealized Losses	0.1	1.1
Entergy Gulf States Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	288.5	238.7
Total Unrealized Gains	69.8	40.9
Total Unrealized Losses		0.8
Entergy Gulf States Louisiana [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	188.9	182.2
Total Unrealized Gains	15.8	15.2
Total Unrealized Losses	0.1	0.3
Entergy Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	287.4	254.0
Total Unrealized Gains	58.3	38.5
Total Unrealized Losses	0.2	1.8
Entergy Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	175.5	149.2
Total Unrealized Gains	48.9	29.7
Total Unrealized Losses	0.1	1.6
Entergy Louisiana [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	111.9	104.8
Total Unrealized Gains	9.4	8.8
Total Unrealized Losses	0.1	0.2
System Energy [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	490.6	423.4
Total Unrealized Gains	72.9	44.9
Total Unrealized Losses	0.3	5.5
System Energy [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	283.6	237.2
Total Unrealized Gains	63.6	35.4
Total Unrealized Losses	0.2	5.4
System Energy [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	207.0	186.2
Total Unrealized Gains	9.3	9.5
Total Unrealized Losses	$ 0.1	$ 0.1