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Investments Investments (Details 6) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Investments in limited partnerships    
Equity in earnings of limited partnerships $ 28us-gaap_IncomeLossFromEquityMethodInvestments $ 50us-gaap_IncomeLossFromEquityMethodInvestments
Indemnity    
Investments in limited partnerships    
Equity in earnings of limited partnerships 2us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
6us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
Indemnity | Equity method of accounting    
Investments in limited partnerships    
Equity in earnings of limited partnerships 2us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ erie_MethodOfAccountingAxis
= erie_EquityMethodOfAccountingMember
5us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ erie_MethodOfAccountingAxis
= erie_EquityMethodOfAccountingMember
Indemnity | Fair value option    
Investments in limited partnerships    
Equity in earnings of limited partnerships 0us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ erie_MethodOfAccountingAxis
= erie_FairValueOptionMember
1us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ erie_MethodOfAccountingAxis
= erie_FairValueOptionMember
Exchange    
Investments in limited partnerships    
Equity in earnings of limited partnerships 26us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
44us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
Exchange | Equity method of accounting    
Investments in limited partnerships    
Equity in earnings of limited partnerships 25us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ erie_MethodOfAccountingAxis
= erie_EquityMethodOfAccountingMember
39us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ erie_MethodOfAccountingAxis
= erie_EquityMethodOfAccountingMember
Exchange | Fair value option    
Investments in limited partnerships    
Equity in earnings of limited partnerships $ 1us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ erie_MethodOfAccountingAxis
= erie_FairValueOptionMember
$ 5us-gaap_IncomeLossFromEquityMethodInvestments
/ dei_LegalEntityAxis
= us-gaap_VariableInterestEntityPrimaryBeneficiaryMember
/ erie_MethodOfAccountingAxis
= erie_FairValueOptionMember