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Equity (Narrative) (Details) (USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 1 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Apr. 30, 2015
Equity [Abstract]      
Stock Options Excluded From Diluted Common Shares Outstanding Calculation 3,500,000etr_StockOptionsExcludedFromDilutedCommonSharesOutstandingCalculation 9,000,000etr_StockOptionsExcludedFromDilutedCommonSharesOutstandingCalculation  
Treasury Stock, Shares, Acquired 325,400us-gaap_TreasuryStockSharesAcquired    
Treasury Stock, Value, Acquired, Cost Method $ 25.1us-gaap_TreasuryStockValueAcquiredCostMethod    
Common stock dividend (in dollars per share) $ 0.83us-gaap_CommonStockDividendsPerShareDeclared $ 0.83us-gaap_CommonStockDividendsPerShareDeclared  
Parent Company [Member]      
Equity [Abstract]      
Shares, Issued 599,136us-gaap_SharesIssued
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= us-gaap_ParentCompanyMember
   
Subsequent Event [Member]      
Equity [Abstract]      
Common stock dividend (in dollars per share)     $ 0.83us-gaap_CommonStockDividendsPerShareDeclared
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