Decommissioning Trust Funds (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Decommissioning Trust Funds [Abstract]
Deferred taxes on unrealized gains/(losses) recorded in OCI for non-regulated decommissioning trusts	$ 211	$ 149
Amortized cost of debt securities	1,637.0	1,530.0
Average coupon rate of debt securities	3.78%
Average duration of debt securities, years	5 years 5 months 6 days
Average maturity of debt securities, years	8 years 6 months 2 days
Proceeds from the dispositions of debt securities	2,074.0	1,360.0	2,606.0
Gains from dispositions of debt securities, gross	39.0	29.0	69.0
Losses from dispositions of debt securities, gross	7.00	11.00	9.00
Entergy Arkansas [Member]
Decommissioning Trust Funds [Abstract]
Amortized cost of debt securities	202.3	197.5
Average coupon rate of debt securities	3.24%
Average duration of debt securities, years	5 years 3 months 12 days
Average maturity of debt securities, years	6 years 1 month 24 days
Proceeds from the dispositions of debt securities	144.3	125.4	367.3
Gains from dispositions of debt securities, gross	3.4	3.9	29.2
Losses from dispositions of debt securities, gross	0.10	0.20	0.80
Entergy Gulf States Louisiana [Member]
Decommissioning Trust Funds [Abstract]
Amortized cost of debt securities	174.1	166.9
Average coupon rate of debt securities	4.74%
Average duration of debt securities, years	5 years 7 months 0 days
Average maturity of debt securities, years	8 years 8 months 13 days
Proceeds from the dispositions of debt securities	131.0	76.8	100.8
Gains from dispositions of debt securities, gross	6.7	2.8	2.0
Losses from dispositions of debt securities, gross	0.04	0.50	0.40
Entergy Louisiana [Member]
Decommissioning Trust Funds [Abstract]
Amortized cost of debt securities	102.6	91.9
Average coupon rate of debt securities	3.64%
Average duration of debt securities, years	5 years 4 months 19 days
Average maturity of debt securities, years	9 years 4 months 22 days
Proceeds from the dispositions of debt securities	27.6	19.9	44.5
Gains from dispositions of debt securities, gross	0.2	0.3	0.7
Losses from dispositions of debt securities, gross	0.04	0.20	0.30
System Energy [Member]
Decommissioning Trust Funds [Abstract]
Amortized cost of debt securities	197.8	175.1
Average coupon rate of debt securities	2.60%
Average duration of debt securities, years	4 years 6 months 9 days
Average maturity of debt securities, years	6 years 1 month 16 days
Proceeds from the dispositions of debt securities	349.4	203.4	322.8
Gains from dispositions of debt securities, gross	3.6	2.7	4.4
Losses from dispositions of debt securities, gross	$ 0.30	$ 1.20	$ 0.60