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Decommissioning Trust Funds (Available For Sale Securities Continuous Unrealized Loss Position Fair Value) (Details) (USD $)
In Millions, unless otherwise specified
6 Months Ended 12 Months Ended
Jun. 30, 2013
Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value   $ 0.7
More than 12 months Fair Value   5.6
Total Fair Value   6.3
Equity Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 29.0 37.0
More than 12 months Fair Value   20.0
Total Fair Value 29.0 57.0
Less than 12 Months Gross Unrealized Losses 1.0 1.0
Total Gross Unrealized Losses 1.0 1.0
Debt Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 700.0 175.0
More than 12 months Fair Value 37.0 48.0
Total Fair Value 737.0 223.0
Less than 12 Months Gross Unrealized Losses 22.0 1.0
More than 12 Months Gross Unrealized Losses 3.0 4.0
Total Gross Unrealized Losses 25.0 5.0
Entergy Arkansas [Member] | Equity Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 0.3 0.2
Total Fair Value 0.3 0.2
Entergy Arkansas [Member] | Debt Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 132.4 24.4
More than 12 months Fair Value 2.4 1.0
Total Fair Value 134.8 25.4
Less than 12 Months Gross Unrealized Losses 3.9 0.2
More than 12 Months Gross Unrealized Losses 0.1  
Total Gross Unrealized Losses 4.0 0.2
Entergy Gulf States Louisiana [Member] | Equity Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 11.7 1.2
More than 12 months Fair Value   1.0
Total Fair Value 11.7 2.2
Less than 12 Months Gross Unrealized Losses 0.4  
Total Gross Unrealized Losses 0.4  
Entergy Gulf States Louisiana [Member] | Debt Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 59.8 9.1
Total Fair Value 59.8 9.1
Less than 12 Months Gross Unrealized Losses 2.4 0.1
Total Gross Unrealized Losses 2.4 0.1
Entergy Louisiana [Member] | Equity Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 0.3  
Total Fair Value 0.3  
More than 12 Months Gross Unrealized Losses   0.1
Total Gross Unrealized Losses   0.1
Entergy Louisiana [Member] | Debt Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 29.0 3.4
More than 12 months Fair Value 0.4 0.5
Total Fair Value 29.4 3.9
Less than 12 Months Gross Unrealized Losses 1.2  
More than 12 Months Gross Unrealized Losses 0.1 0.1
Total Gross Unrealized Losses 1.3 0.1
System Energy [Member] | Equity Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 0.8 1.4
More than 12 months Fair Value   13.0
Total Fair Value 0.8 14.4
More than 12 Months Gross Unrealized Losses   0.2
Total Gross Unrealized Losses   0.2
System Energy [Member] | Debt Securities [Member]
   
Schedule of Available-for-sale Securities [Line Items]    
Less than 12 months Fair Value 92.2 15.5
Total Fair Value 92.2 15.5
Less than 12 Months Gross Unrealized Losses 1.8 0.1
Total Gross Unrealized Losses $ 1.8 $ 0.1