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Indemnity Earnings Per Share (Details) (Indemnity, USD $)
In Millions, except Share data, unless otherwise specified
3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Class A                      
Income available to stockholders (Basic EPS:)                      
Allocated net income (numerator) (in dollars)                 $ 167us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 162us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 159us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Weighted shares (denominator) (in shares)                 46,247,876us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
46,660,651us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
47,357,836us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Per-share amount (in dollars per share) $ 0.54us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 1.01us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 1.05us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.99us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.75us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.98us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.95us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.78us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 3.59us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 3.46us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 3.38us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Dilutive effect of stock-based awards                      
Allocated net income (numerator) (in dollars)                 0us-gaap_AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
0us-gaap_AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
0us-gaap_AmountOfDilutiveSecuritiesStockOptionsAndRestrictiveStockUnits
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Weighted shares (denominator) (in shares)                 267,558us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
94,306us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
84,397us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Assumed conversion of Class B shares                      
Allocated net income (numerator) (in dollars)                 1us-gaap_DilutiveSecuritiesEffectOnBasicEarningsPerShareOther
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
1us-gaap_DilutiveSecuritiesEffectOnBasicEarningsPerShareOther
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
1us-gaap_DilutiveSecuritiesEffectOnBasicEarningsPerShareOther
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Weighted shares (denominator) (in shares)                 6,100,800erie_IncrementalCommonSharesAttributableToConversionOfConvertibleCommonStock
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
6,100,800erie_IncrementalCommonSharesAttributableToConversionOfConvertibleCommonStock
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
6,105,600erie_IncrementalCommonSharesAttributableToConversionOfConvertibleCommonStock
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Income available to stockholders on equivalent shares (Diluted EPS:)                      
Allocated net income (numerator) (in dollars)                 168us-gaap_NetIncomeLossAttributableToParentDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
163us-gaap_NetIncomeLossAttributableToParentDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
160us-gaap_NetIncomeLossAttributableToParentDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Weighted shares (denominator) (in shares)                 52,616,234us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
52,855,757us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
53,547,833us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Per-share amount (in dollars per share) $ 0.48us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.90us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.94us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.88us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.67us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.87us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.84us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 0.69us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 3.18us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 3.08us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
$ 2.99us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassAMember
Class B                      
Reconciliation of the numerators and denominators used in the basic and diluted per-share computations                      
Ratio for converting shares of Class B common stock into shares of Class A common stock (as a percent) 2400.00%erie_CommonStockConversionRatio
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
      2400.00%erie_CommonStockConversionRatio
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
      2400.00%erie_CommonStockConversionRatio
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
2400.00%erie_CommonStockConversionRatio
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
 
Income available to stockholders (Basic EPS:)                      
Allocated net income (numerator) (in dollars)                 1us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
1us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
1us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
Weighted shares (denominator) (in shares)                 2,542us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
2,542us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
2,544us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
Per-share amount (in dollars per share) $ 81us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 151.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 158.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 149.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 113.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 147.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 142.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 117.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 539.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 520.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 505.00us-gaap_EarningsPerShareBasic
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
Income available to stockholders on equivalent shares (Diluted EPS:)                      
Allocated net income (numerator) (in dollars)                 $ 1us-gaap_NetIncomeLossAttributableToParentDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 1us-gaap_NetIncomeLossAttributableToParentDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 1us-gaap_NetIncomeLossAttributableToParentDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
Weighted shares (denominator) (in shares)                 2,542us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
2,542us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
2,544us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
Per-share amount (in dollars per share) $ 81us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 151.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 158.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 149.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 113.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 147.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 142.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 117.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 538.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 519.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember
$ 505.00us-gaap_EarningsPerShareDiluted
/ dei_LegalEntityAxis
= us-gaap_ParentCompanyMember
/ us-gaap_StatementClassOfStockAxis
= us-gaap_CommonClassBMember