Summary of Significant Accounting Policies (Cash Equivalents, Short-term Investments, and Stock-Based Compensation) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Excess tax benefit from share-based compensation	$ 3.1	$ 0.6	$ 1.0

Reductions in the entity's income taxes that arise when compensation cost (from non-qualified share-based compensation) recognized on the entity's tax return exceeds compensation cost from equity-based compensation recognized in financial statements. This element represents the current year addition to the available pool of windfall tax benefit.

No definition available.

Name:	egn_ExcessTaxBenefitFromShareBasedCompensation
Namespace Prefix:	egn_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration