Indemnity Supplemental Information (Details) (USD $) In Millions, unless otherwise specified									6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011	Dec. 31, 2010	Jun. 30, 2012 Indemnity	Dec. 31, 2011 Indemnity	Jun. 30, 2011 Indemnity	Dec. 31, 2010 Indemnity	Jun. 30, 2012 Indemnity Erie Family Life Insurance Company ("EFL")	Jun. 30, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Jun. 30, 2012 Exchange	Dec. 31, 2011 Exchange	Dec. 31, 2010 Exchange	Jun. 30, 2012 Reclassifications and eliminations	Dec. 31, 2011 Reclassifications and eliminations
Available-for-sale securities, at fair value:
Fixed maturities	$ 8,079	$ 7,840			$ 510	$ 548					$ 7,569	$ 7,292
Equity securities	631	589			26	25					605	564
Trading securities, at fair value	2,518	2,335			28	27					2,490	2,308
Limited partnerships	1,282	1,290			199	208					1,083	1,082
Other invested assets	20	20			1	1					19	19
Total investments	12,530	12,074			764	809					11,766	11,265
Cash and cash equivalents	240	185	109	430	13	11	48	310			227	174
Premiums receivable from policyholders	1,073	976									1,073	976
Reinsurance recoverable	168	166									168	166
Deferred income taxes	21	19			21	19
Deferred acquisition costs	500	487									500	487
Other assets	510	441			115	119					395	322
Receivables from the Exchange and other affiliates					277	254								(277)	(254)
Note receivable from EFL					25	25								(25)	(25)
Total assets	15,042	14,348			1,215	1,237					14,129	13,390		(302)	(279)
Liabilities
Losses and loss expense reserves	3,613	3,499									3,613	3,499
Life policy and deposit contract reserves	1,706	1,671									1,706	1,671
Unearned premiums	2,331	2,178									2,331	2,178
Deferred income taxes	235	147									235	147
Other liabilities, prior to consolidation eliminations	560	560			449	456					413	383		(302)	(279)
Total liabilities	8,445	8,055			449	456					8,298	7,878		(302)	(279)
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	766	781			766	781
Noncontrolling interest in consolidated entity - Exchange	5,831	5,512									5,831	5,512
Total equity	6,597	6,293		6,334	766	781		912			5,831	5,512	5,422
Total liabilities, shareholders' equity and noncontrolling interest	15,042	14,348			1,215	1,237					14,129	13,390		(302)	(279)
Note receivable from EFL, annual interest rate (as a percent)									6.70%
Interest income									$ 0.8	$ 0.8