Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 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	$ 1,061	$ 1,005	$ 3,138	$ 2,972
Net investment income	108	110	326	322
Net realized investment (losses) gains	(422)	205	(234)	117
Net impairment losses recognized in earnings	0	0	0	(6)
Equity in earnings of limited partnerships	40	28	150	58
Service agreement and other revenue	9	9	26	26
Total revenues (losses)	796	1,357	3,406	3,489
Benefits and expenses
Insurance losses and loss expenses	848	710	2,724	2,208
Policy acquisition and underwriting expenses	253	242	749	699
Total benefits and expenses	1,101	952	3,473	2,907
Income (loss) before income taxes	(305)	405	(67)	582
Provision for income taxes	(125)	130	(54)	176
Net income (loss)	(180)	275	(13)	406	660
Erie Family Life Insurance Company ("EFL")
Benefits and expenses
Income (loss) before income taxes	13	16	38	37
Erie Family Life Insurance Company ("EFL") | Investment operations segment
Segment information
Total investment revenues	29	27	83	79
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	280	266	816	773
Service agreement and other revenue	8	9	25	26
Total revenues (losses)	288	275	841	799
Benefits and expenses
Cost of management operations	226	217	667	626
Total benefits and expenses	226	217	667	626
Income (loss) before income taxes	62	58	174	173
Provision for income taxes	22	22	61	61
Net income (loss)	40	36	113	112
Property and casualty insurance operations segment
Revenues
Premiums earned/life policy revenue	1,045	990	3,089	2,926
Total revenues (losses)	1,045	990	3,089	2,926
Benefits and expenses
Insurance losses and loss expenses	823	690	2,653	2,145
Policy acquisition and underwriting expenses	302	288	882	829
Total benefits and expenses	1,125	978	3,535	2,974
Income (loss) before income taxes	(80)	12	(446)	(48)
Provision for income taxes	(28)	4	(156)	(17)
Net income (loss)	(52)	8	(290)	(31)
Life insurance operations segment
Revenues
Premiums earned/life policy revenue	16	16	50	48
Service agreement and other revenue	1	0	1	0
Total revenues (losses)	17	16	51	48
Benefits and expenses
Insurance losses and loss expenses	26	21	75	67
Policy acquisition and underwriting expenses	7	6	21	23
Total benefits and expenses	33	27	96	90
Income (loss) before income taxes	(16)	(11)	(45)	(42)
Provision for income taxes	(6)	(4)	(16)	(15)
Net income (loss)	(10)	(7)	(29)	(27)
Investment operations segment
Revenues
Net investment income	111	113	334	330
Net realized investment (losses) gains	(422)	205	(234)	117
Net impairment losses recognized in earnings	0	0	0	(6)
Equity in earnings of limited partnerships	40	28	150	58
Total revenues (losses)	(271)	346	250	499
Benefits and expenses
Income (loss) before income taxes	(271)	346	250	499
Provision for income taxes	(113)	108	57	147
Net income (loss)	(158)	238	193	352
Eliminations
Revenues
Premiums earned/life policy revenue		(1)	(1)	(2)
Net investment income	(3)	(3)	(8)	(8)
Management fee revenue	(280)	(266)	(816)	(773)
Total revenues (losses)	(283)	(270)	(825)	(783)
Benefits and expenses
Cost of management operations	(226)	(217)	(667)	(626)
Insurance losses and loss expenses	(1)	(1)	(4)	(4)
Policy acquisition and underwriting expenses	(56)	(52)	(154)	(153)
Total benefits and expenses	$ (283)	$ (270)	$ (825)	$ (783)