Indemnity Supplemental Information (Details 2) (USD $) In Millions, unless otherwise specified	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
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012 Indemnity	Sep. 30, 2011 Indemnity	Sep. 30, 2012 Indemnity	Sep. 30, 2011 Indemnity	Sep. 30, 2012 Indemnity Management operations	Sep. 30, 2011 Indemnity Management operations	Sep. 30, 2012 Indemnity Management operations	Sep. 30, 2011 Indemnity Management operations	Sep. 30, 2011 Indemnity Life insurance operations	Mar. 31, 2011 Indemnity Life insurance operations	Sep. 30, 2012 Indemnity Investment operations	Sep. 30, 2011 Indemnity Investment operations	Sep. 30, 2012 Indemnity Investment operations	Sep. 30, 2011 Indemnity Investment operations	Mar. 31, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Sep. 30, 2012 Exchange	Sep. 30, 2011 Exchange	Sep. 30, 2012 Exchange	Sep. 30, 2011 Exchange	Mar. 31, 2011 Exchange Erie Family Life Insurance Company ("EFL")
Condensed financial statements
Management fee revenue, net									$ 305	$ 280	$ 882	$ 816
Service agreement revenue	8	9	24	26					8	8	23	25
Total revenues	1,460	796	4,140	3,406					313	288	905	841	10
Cost of management operations									247	226	734	667
Total benefits and expenses	1,190	1,101	3,406	3,473									7
Net investment income	105	108	326	326	4	4	12	12							4	4	12	12		101	104	314	314
Net realized gains (losses) on investment	169	(422)	358	(234)	2	(6)	4	1							2	(6)	4	1		167	(416)	354	(235)
Net impairment losses recognized in earnings	0	0	0	0											0	0	0	0			(0.3)	(0.1)	(0.3)
Equity in earnings of limited partnerships	41	40	99	150											6	7	10	25
Income (loss) from operations before income taxes and noncontrolling interest	270	(305)	734	(67)	78	67	197	215	66	62	171	174	3		12	5	26	38
Provision for income taxes	86	(125)	234	(54)	27	20	67	72
Net income	$ 51	$ 47	$ 130	$ 143	$ 51	$ 47	$ 130	$ 143
Percent income attributable to Indemnity shareholder interest									100.00%	100.00%	100.00%	100.00%		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%