Income Taxes Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
Jun. 30, 2017	Mar. 31, 2017
Reduction in income tax expense related to permanent difference for nuclear decommissioning liability, net of unrecognized tax benefits	$ 373.0
Write-off of deferred tax asset resulting from implementation of accounting standard		$ 11.5
Fitzpatrick [Member]
Income tax benefit resulting from sale of FitzPatrick		$ 44.0

Reduction in income tax expense related to the recognition, for income tax purposes, of nuclear decommissioning liability, resulting in permanent differences under the income tax accounting standards.

No definition available.

Name:	etr_Reductioninincometaxexpenserelatedtopermanentdifferencefornucleardecommissioningliabilitynetofunrecognizedtaxbenefits
Namespace Prefix:	etr_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration