Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010
Segment Information
Threshold percentage for disclosure of revenue from a single customer or agent (as a percent)			10.00%
Revenues
Premiums earned/life policy revenue	$ 1,047	$ 989	$ 2,077	$ 1,967
Net investment income	113	108	218	212
Net realized investment gains (losses)	39	(213)	188	(88)
Net impairment losses recognized in earnings	0	(4)	0	(6)
Equity in earnings of limited partnerships	38	27	110	30
Service agreement and other revenue	8	9	17	17
Total revenues	1,245	916	2,610	2,132
Benefits and expenses
Insurance losses and loss expenses	1,170	737	1,876	1,498
Policy acquisition and underwriting expenses	249	230	496	457
Total benefits and expenses	1,419	967	2,372	1,955
Income (loss) before income taxes	(174)	(51)	238	177
Provision for income taxes	(67)	(20)	71	46
Net (loss) income	(107)	(31)	167	131	660
Erie Family Life Insurance Company ("EFL")
Benefits and expenses
Income (loss) before income taxes	12	11	25	21
Erie Family Life Insurance Company ("EFL") | Investment operations segment
Segment information
Total investment revenues	27	25	54	52
Management operations segment
Segment information
Indemnity's maximum management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)			25.00%
Revenues
Management fee revenue	285	270	536	507
Service agreement and other revenue	9	9	17	17
Total revenues	294	279	553	524
Benefits and expenses
Cost of management operations	230	217	441	409
Total benefits and expenses	230	217	441	409
Income (loss) before income taxes	64	62	112	115
Provision for income taxes	22	21	39	39
Net (loss) income	42	41	73	76
Property and casualty insurance operations segment
Revenues
Premiums earned/life policy revenue	1,030	974	2,044	1,936
Total revenues	1,030	974	2,044	1,936
Benefits and expenses
Insurance losses and loss expenses	1,147	717	1,830	1,455
Policy acquisition and underwriting expenses	298	275	580	540
Total benefits and expenses	1,445	992	2,410	1,995
Income (loss) before income taxes	(415)	(18)	(366)	(59)
Provision for income taxes	(145)	(7)	(128)	(21)
Net (loss) income	(270)	(11)	(238)	(38)
Life insurance operations segment
Revenues
Premiums earned/life policy revenue	18	16	34	32
Service agreement and other revenue	(1)	0	0	0
Total revenues	17	16	34	32
Benefits and expenses
Insurance losses and loss expenses	25	22	49	46
Policy acquisition and underwriting expenses	7	9	14	18
Total benefits and expenses	32	31	63	64
Income (loss) before income taxes	(15)	(15)	(29)	(32)
Provision for income taxes	(5)	(5)	(10)	(11)
Net (loss) income	(10)	(10)	(19)	(21)
Investment operations segment
Revenues
Net investment income	115	110	223	217
Net realized investment gains (losses)	39	(213)	188	(88)
Net impairment losses recognized in earnings	0	(4)	0	(6)
Equity in earnings of limited partnerships	38	27	110	30
Total revenues	192	(80)	521	153
Benefits and expenses
Income (loss) before income taxes	192	(80)	521	153
Provision for income taxes	61	(29)	170	39
Net (loss) income	131	(51)	351	114
Eliminations
Revenues
Premiums earned/life policy revenue	(1)	(1)	(1)	(1)
Net investment income	(2)	(2)	(5)	(5)
Management fee revenue	(285)	(270)	(536)	(507)
Total revenues	(288)	(273)	(542)	(513)
Benefits and expenses
Cost of management operations	(230)	(217)	(441)	(409)
Insurance losses and loss expenses	(2)	(2)	(3)	(3)
Policy acquisition and underwriting expenses	(56)	(54)	(98)	(101)
Total benefits and expenses	$ (288)	$ (273)	$ (542)	$ (513)