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Guarantees and Indemnifications (Details) (USD $)
In Millions, unless otherwise specified
Mar. 31, 2015
Guarantee Of Financial Obligations Of Npt [Member]  
Guarantee Obligations [Line Items]  
Guarantee Obligations Maximum Exposure $ 25.0us-gaap_GuaranteeObligationsMaximumExposure
/ us-gaap_GuaranteeObligationsByNatureAxis
= es_GuaranteeOfFinancialObligationsOfNptMember
Various Subsidiary Surety Bonds And Performance Guarantees Expiring Between 2015 And 2016 [Member]  
Guarantee Obligations [Line Items]  
Guarantee Obligations Maximum Exposure 54.6us-gaap_GuaranteeObligationsMaximumExposure
/ us-gaap_GuaranteeObligationsByNatureAxis
= es_VariousSubsidiarySuretyBondsAndPerformanceGuaranteesExpiringBetween2015And2016Member
Guarantee Of Rocky River Reality And Nusco Lease Payments For Real Estate And Vehicles Expiring 2019 Through 2024 [Member]  
Guarantee Obligations [Line Items]  
Guarantee Obligations Maximum Exposure $ 13.8us-gaap_GuaranteeObligationsMaximumExposure
/ us-gaap_GuaranteeObligationsByNatureAxis
= es_GuaranteeOfRockyRiverRealityAndNuscoLeasePaymentsForRealEstateAndVehiclesExpiring2019Through2024Member