Decommissioning Trust Funds (Securities Held) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 4,453.0	$ 4,190.0
Total Unrealized Gains	999.0	778.0
Total Unrealized Losses	5.0	6.0
Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	2,705.0	2,459.0
Total Unrealized Gains	897.0	662.0
Total Unrealized Losses		1.0
Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	1,748.0	1,731.0
Total Unrealized Gains	102.0	116.0
Total Unrealized Losses	5.0	5.0
Entergy Arkansas [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	643.2	600.6
Total Unrealized Gains	168.3	130.6
Total Unrealized Losses	0.5	0.2
Entergy Arkansas [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	419.8	384.0
Total Unrealized Gains	156.1	116.1
Entergy Arkansas [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	223.4	216.6
Total Unrealized Gains	12.2	14.5
Total Unrealized Losses	0.5	0.2
Entergy Gulf States Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	511.7	477.4
Total Unrealized Gains	113.3	85.6
Total Unrealized Losses	0.3	0.1
Entergy Gulf States Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	320.2	288.5
Total Unrealized Gains	99.3	69.8
Entergy Gulf States Louisiana [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	191.5	188.9
Total Unrealized Gains	14.0	15.8
Total Unrealized Losses	0.3	0.1
Entergy Louisiana [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	308.5	287.4
Total Unrealized Gains	75.8	58.3
Total Unrealized Losses	0.2	0.2
Entergy Louisiana [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	196.1	175.5
Total Unrealized Gains	67.3	48.9
Total Unrealized Losses		0.1
Entergy Louisiana [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	112.4	111.9
Total Unrealized Gains	8.5	9.4
Total Unrealized Losses	0.2	0.1
System Energy [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	528.2	490.6
Total Unrealized Gains	101.8	72.9
Total Unrealized Losses	0.1	0.3
System Energy [Member] | Equity Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	318.1	283.6
Total Unrealized Gains	93.4	63.6
Total Unrealized Losses		0.2
System Energy [Member] | Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	210.1	207.0
Total Unrealized Gains	8.4	9.3
Total Unrealized Losses	$ 0.1	$ 0.1