Income Taxes Income Taxes (Summary of Interest on Income Taxes Expense Related to Unrecognized Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ (4.0)	$ 4.0	$ 7.0
Entergy Arkansas [Member]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(0.8)	1.4	0.2
Entergy Louisiana [Member]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(10.8)	(3.7)	3.8
Entergy Mississippi [Member]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	0.2	0.5	0.2
Entergy New Orleans [Member]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(0.8)	2.0	0.6
Entergy Texas [Member]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	(0.2)	0.2	0.5
System Energy [Member]
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	$ (2.6)	$ 1.3	$ 4.7