Indemnity Supplemental Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed financial statements
Management fee revenue, net
Service agreement revenue									32	34	35
Total revenues	1,372	1,460	1,160	1,520	1,418	796	1,245	1,365	5,512	4,824	4,890
Cost of management operations
Net premiums earned									4,493	4,214	3,987
Losses and loss expenses									3,480	3,444	2,900
Policy acquisition and underwriting expenses									1,133	1,022	969
Total benefits and expenses	1,207	1,190	1,230	986	993	1,101	1,419	953	4,613	4,466	3,891
Net investment income									438	433	433
Net realized gains (losses) on investment									418	(4)	313
Net impairment losses recognized in earnings									0	(2)	(6)
Equity in earnings of limited partnerships									131	149	128
Income (loss) from operations before income taxes and noncontrolling interest	165	270	(70)	534	425	(305)	(174)	412	899	358	999
Net income attributable to Indemnity	30	51	43	36	26	47	52	44	160	169	162
Indemnity
Condensed financial statements
Net investment income									16	16	37
Net realized gains (losses) on investment									5	3	(1)
Net impairment losses recognized in earnings									0	0	(1)
Income (loss) from operations before income taxes and noncontrolling interest									241	256	269
Provision for income taxes									81	87	107
Net income attributable to Indemnity									160	169	162
Reimbursements from Exchange for claims handling services									343	325	293
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
Indemnity | Management operations
Condensed financial statements
Management fee revenue, net									1,157	1,067	1,009
Service agreement revenue									31	33	34
Total revenues									1,188	1,100	1,043
Cost of management operations									983	892	841
Income (loss) from operations before income taxes and noncontrolling interest									205	208	202
Percent income attributable to Indemnity shareholder interest	100.00%				100.00%				100.00%	100.00%	100.00%
Indemnity | Property and casualty insurance operations
Condensed financial statements
Net premiums earned											216
Losses and loss expenses											155
Policy acquisition and underwriting expenses											61
Income (loss) from operations before income taxes and noncontrolling interest											0
Percent income attributable to Indemnity shareholder interest											5.50%
Indemnity | Life insurance operations
Condensed financial statements
Total revenues										10	37
Total benefits and expenses										7	26
Income (loss) from operations before income taxes and noncontrolling interest										3	11
Percent income attributable to Indemnity shareholder interest								21.60%			21.60%
Indemnity | Investment operations
Condensed financial statements
Net investment income									16	16	37
Net realized gains (losses) on investment									5	3	(1)
Net impairment losses recognized in earnings									0	0	(1)
Equity in earnings of limited partnerships									15	26	21
Income (loss) from operations before income taxes and noncontrolling interest									36	45	56
Indemnity | Erie Family Life Insurance Company (EFL)
Condensed financial statements
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%
Reimbursements from EFL for employee costs									30	28	27
Annual rentals paid to EFL									0.4	0.4	0.4
Exchange
Condensed financial statements
Net investment income									422	417	396
Net realized gains (losses) on investment									413	(7)	314
Net impairment losses recognized in earnings									$ 0	$ (2)	$ (5)
Exchange | Erie Family Life Insurance Company (EFL)
Condensed financial statements
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%