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Postretirement Benefits (Details 3) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Postretirement Benefits    
Funded status at end of period $ (189)us-gaap_DefinedBenefitPlanFundedStatusOfPlan $ (95)us-gaap_DefinedBenefitPlanFundedStatusOfPlan
Pension liability recorded in the Consolidated Statement of Financial Position:    
Pension liabilities - due within one year 0us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities (1)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansCurrentLiabilities
Pension liabilities - due after one year (189)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent (94)us-gaap_PensionAndOtherPostretirementDefinedBenefitPlansLiabilitiesNoncurrent
Net amount recognized (189)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet (95)us-gaap_DefinedBenefitPlanAmountsRecognizedInBalanceSheet
Employee pension plan    
Postretirement Benefits    
Funding target (as a percentage of the funding target liability) 100.00%erie_DefinedBenefitPlanFundingTargetPercentage
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember		  
Expected employer contribution during next fiscal year $ 17us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
/ us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis
= us-gaap_PensionPlansDefinedBenefitMember