Indemnity Supplemental Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended																									12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Erie Family Life Insurance Company ("EFL")	Dec. 31, 2010 Erie Family Life Insurance Company ("EFL")	Dec. 31, 2009 Erie Family Life Insurance Company ("EFL")	Dec. 31, 2011 Indemnity facility	Dec. 31, 2010 Indemnity	Dec. 31, 2009 Indemnity	Dec. 31, 2011 Indemnity Management operations	Dec. 31, 2010 Indemnity Management operations	Dec. 31, 2009 Indemnity Management operations	Dec. 31, 2010 Indemnity Property and casualty insurance operations	Dec. 31, 2009 Indemnity Property and casualty insurance operations	Dec. 31, 2011 Indemnity Life insurance operations	Dec. 31, 2010 Indemnity Life insurance operations	Dec. 31, 2009 Indemnity Life insurance operations	Dec. 31, 2011 Indemnity Investment operations	Dec. 31, 2010 Indemnity Investment operations	Dec. 31, 2009 Indemnity Investment operations	Dec. 31, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Dec. 31, 2010 Indemnity Erie Family Life Insurance Company ("EFL")	Dec. 31, 2009 Indemnity Erie Family Life Insurance Company ("EFL")	Mar. 31, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Mar. 30, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Dec. 31, 2011 Exchange	Dec. 31, 2010 Exchange	Dec. 31, 2009 Exchange	Mar. 31, 2011 Exchange Erie Family Life Insurance Company ("EFL")	Mar. 31, 2011 Exchange Erie Family Life Insurance Company ("EFL") Life insurance operations
Condensed financial statements
Management fee revenue, net																		$ 1,067	$ 1,009	$ 965
Service agreement revenue									34	35	36							33	34	35
Total revenues	1,418	796	1,245	1,365	1,401	1,357	916	1,216	4,824	4,890	4,255							1,100	1,043	1,000			10	37	27
Cost of management operations																		892	841	813
Premiums earned, net									4,214	3,987	3,869										216	209
Losses and loss expenses									3,444	2,900	2,728										155	145
Policy acquisition and underwriting expenses									1,022	969	1,003										61	63
Total benefits and expenses	993	1,101	1,419	953	984	952	967	988	4,466	3,891	3,731												7	26	25
Net investment income									433	433	433				16	37	42									16	37	42						417	396	391
Net realized gains (losses) on investments									(4)	313	412				3	(1)	10									3	(1)	10						(7)	314	402
Net impairment losses recognized in earnings									(2)	(6)	(126)															0	(1)	(12)
Equity in earnings (losses) of limited partnerships									149	128	(369)															26	21	(76)
Income from operations before taxes	425	(305)	(174)	412	417	405	(51)	228	358	999	524	50	50	10	256	269	154	208	202	187	0	1	3	11	2	45	56	(36)
Provision for income taxes															87	107	46
Net income	281	(180)	(107)	274	254	275	(31)	162	268	660	446				169	162	108
Percent Income attributable to Indemnity shareholder interest																		100.00%	100.00%	100.00%	5.50%	5.50%		21.60%	21.60%
Indemnity's ownership interest in EFL prior to and through March 31, 2011 (as a percent)																																	21.60%
Indemnity's ownership interest in EFL sold to the Exchange (as a percent)																																21.60%
Exchange's ownership interest in EFL prior to and through March 31, 2011 (as a percent)																																					78.40%
Exchange's ownership interest in EFL after March 31, 2011 (as a percent)																																						100.00%
Reimbursements from Exchange for claims handling services															325	293	282
Reimbursements from EFL for employee costs																													28	27	32
Number of field office facilities leased from the Exchange (in number of facilities)															3
Rent expense on office space leased from Exchange															6	6	6
Annual rentals paid to EFL																													$ 0.4	$ 0.4	$ 0.3