Indemnity Supplemental Information (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended	3 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended	9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		12 Months Ended			3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010	Sep. 30, 2011 Indemnity	Sep. 30, 2010 Indemnity	Sep. 30, 2011 Indemnity	Sep. 30, 2010 Indemnity	Dec. 31, 2010 Indemnity	Sep. 30, 2010 Indemnity Property and casualty insurance operations	Sep. 30, 2010 Indemnity Property and casualty insurance operations	Mar. 31, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Sep. 30, 2011 Indemnity Management operations	Sep. 30, 2010 Indemnity Management operations	Sep. 30, 2011 Indemnity Management operations	Sep. 30, 2010 Indemnity Management operations	Sep. 30, 2010 Indemnity Life insurance operations	Sep. 30, 2011 Indemnity Life insurance operations	Sep. 30, 2010 Indemnity Life insurance operations	Sep. 30, 2011 Indemnity Investment operations	Sep. 30, 2010 Indemnity Investment operations	Sep. 30, 2011 Indemnity Investment operations	Sep. 30, 2010 Indemnity Investment operations	Sep. 30, 2011 Exchange	Sep. 30, 2010 Exchange	Sep. 30, 2011 Exchange	Sep. 30, 2010 Exchange	Dec. 31, 2010 Exchange	Mar. 31, 2011 Exchange Erie Family Life Insurance Company ("EFL")	Sep. 30, 2011 Exchange Life insurance operations	Sep. 30, 2011 Erie Family Life Insurance Company ("EFL")	Sep. 30, 2010 Erie Family Life Insurance Company ("EFL")	Sep. 30, 2011 Erie Family Life Insurance Company ("EFL")	Sep. 30, 2010 Erie Family Life Insurance Company ("EFL")
Condensed financial statements
Management fee revenue, net														$ 280	$ 266	$ 816	$ 773
Service agreement revenue	9	9	26	26										8	9	25	26
Total revenues	796	1,357	3,406	3,489										288	275	841	799	10	10	28
Cost of management operations														226	217	667	626
Income (loss) from operations before income taxes	(305)	405	(67)	582		67	82	215	223		1	(3)		62	58	174	173	3	3	8	5	20	38	45								13	16	38	37
Net premiums earned	1,061	1,005	3,138	2,972							55	161
Losses and loss expenses	848	710	2,724	2,208							38	118
Policy acquisition and underwriting expenses	253	242	749	699							16	46
Total benefits and expenses	1,101	952	3,473	2,907														7	7	20
Net investment income	108	110	326	322		4	10	12	28												4	10	12	28	104	100	314	294
Net realized (losses) gains on investments	(422)	205	(234)	117		(6)	5	1	7												(6)	5	1	7	(416)	200	(235)	110
Net impairment losses recognized in earnings	0	0	0	(6)		0	0	0	(1)												0	0	0	(1)	0	0	0	(5)
Equity in earnings of limited partnerships	40	28	150	58																	7	5	25	11
Provision for income taxes	(125)	130	(54)	176		20	28	72	73
Net income	$ (180)	$ 275	$ (13)	$ 406	$ 660	$ 47	$ 54	$ 143	$ 150	$ 162											$ 47		$ 143				$ (156)		$ 498
Percent Income attributable to Indemnity shareholder interest (as a percent)											5.50%	5.50%		100.00%	100.00%	100.00%	100.00%	21.60%	21.60%	21.60%
Indemnity's ownership interest in EFL prior to and through March 31, 2011 (as a percent)													21.60%
Exchange's ownership interest in EFL prior to and through March 31, 2011 (as a percent)																														78.40%
Indemnity's ownership interest in EFL sold to the Exchange (as a percent)													21.60%
Exchange's ownership interest in EFL after March 31, 2011 (as a percent)																															100.00%