Risk Management and Fair Values (Narrative) (Details) TWh in Millions, $ in Millions	3 Months Ended			9 Months Ended		12 Months Ended
	Dec. 31, 2017 TWh	Sep. 30, 2017 USD ($) GWh MMBTU	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) GWh MMBTU	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) counterparty
Risk Management and Fair Values [Abstract]
Letters of Credit Outstanding, Amount		$ 28.0		$ 28.0
Cash collateral posted		1.0		1.0		$ 2.0
Derivative, Collateral, Obligation to Return Cash		4.0		4.0
Letters of Credit Held		28.0		28.0
Cash flow hedges relating to power sales as part of net unrealized gains				59.0
Reclassified from accumulated other comprehensive income (OCI) to operating revenues				37.0
Number of Derivative Contract Counterparties in a Liability Position | counterparty						3
Maturity of cash flow hedges, Tax		$ 8.0	$ 13.0	$ 30.0	$ 83.0
Maximum length of time over which Company is currently hedging the variability in future cash flows for forecasted power transactions, years				3 years 6 months
Total volume of natural gas swaps outstanding (MMBtu) | MMBTU		27,702,900		27,702,900
Total volume of fixed transmission rights outstanding | GWh		75,621		75,621
Change in cash flow hedges due to ineffectiveness		$ 2.4	6.4	$ 6.4	6.1
Dollar amount of hedge contract in a liability position						$ 8.0
Fair Value Measurement With Unobservable Inputs Reconciliation Recurring Basis Asset and Liability Unrealized Gains (Loss) Included in Earnings		0.4	1.0	1.0	1.0
Entergy Arkansas [Member]
Risk Management and Fair Values [Abstract]
Letters of Credit Outstanding, Amount		$ 0.2		$ 0.2		0.3
Total volume of fixed transmission rights outstanding | GWh		17,014		17,014
Entergy Louisiana [Member]
Risk Management and Fair Values [Abstract]
Total volume of natural gas swaps outstanding (MMBtu) | MMBTU		21,673,200		21,673,200
Total volume of fixed transmission rights outstanding | GWh		33,700		33,700
Entergy Mississippi [Member]
Risk Management and Fair Values [Abstract]
Letters of Credit Outstanding, Amount		$ 0.1		$ 0.1		$ 0.1
Total volume of natural gas swaps outstanding (MMBtu) | MMBTU		5,042,700		5,042,700
Total volume of fixed transmission rights outstanding | GWh		10,214		10,214
Entergy New Orleans [Member]
Risk Management and Fair Values [Abstract]
Total volume of natural gas swaps outstanding (MMBtu) | MMBTU		987,000		987,000
Total volume of fixed transmission rights outstanding | GWh		3,839		3,839
Entergy Texas [Member]
Risk Management and Fair Values [Abstract]
Total volume of fixed transmission rights outstanding | GWh		10,326		10,326
Electricity Swaps And Options [Member]
Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset and Liability, Realized Gain (Loss) Included In Earnings		$ 2.0	6.0	$ 6.0	(3.0)
Fixed Transmission Rights (FTRs) [Member]
Fair Value, Measurement With Unobservable Inputs Reconciliation, Recurring Basis, Asset and Liability, Realized Gain (Loss) Included In Earnings		$ 0.0	$ 0.0	$ 1.0	$ 0.0
Subsequent Event [Member]
Risk Management and Fair Values [Abstract]
Planned generation sold forward from non utility nuclear power plants for the remainder of the period	88.00%
Planned Generation From Non Nuclear Power Plants Sold Forward Under Financial Hedges	31.00%
Total planned generation for remainder of the period | TWh	7.6