Indemnity Supplemental Information (Details) (USD $) In Millions, unless otherwise specified									9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Dec. 31, 2010	Sep. 30, 2012 Indemnity	Dec. 31, 2011 Indemnity	Sep. 30, 2011 Indemnity	Dec. 31, 2010 Indemnity	Sep. 30, 2012 Indemnity Erie Family Life Insurance Company ("EFL")	Sep. 30, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Sep. 30, 2012 Exchange	Dec. 31, 2011 Exchange	Dec. 31, 2010 Exchange	Sep. 30, 2012 Reclassifications and eliminations	Dec. 31, 2011 Reclassifications and eliminations
Available-for-sale securities, at fair value:
Fixed maturities	$ 8,170	$ 7,840			$ 547	$ 548					$ 7,623	$ 7,292
Equity securities	653	589			29	25					624	564
Trading securities, at fair value	2,669	2,335			30	27					2,639	2,308
Limited partnerships	1,278	1,290			195	208					1,083	1,082
Other invested assets	21	20			1	1					20	19
Total investments	12,791	12,074			802	809					11,989	11,265
Cash and cash equivalents	404	185	76	430	12	11	34	310			392	174
Premiums receivable from policyholders	1,100	976									1,100	976
Reinsurance recoverable	165	166									165	166
Deferred income taxes	16	19			16	19
Deferred acquisition costs	505	487									505	487
Other assets	563	441			115	119					448	322
Receivables from the Exchange and other affiliates					286	254								(286)	(254)
Note receivable from EFL					25	25								(25)	(25)
Total assets	15,544	14,348			1,256	1,237					14,599	13,390		(311)	(279)
Liabilities
Losses and loss expense reserves	3,598	3,499									3,598	3,499
Life policy and deposit contract reserves	1,721	1,671									1,721	1,671
Unearned premiums	2,420	2,178									2,420	2,178
Deferred income taxes	367	147									367	147
Other liabilities, prior to consolidation eliminations	595	560			474	456					432	383		(311)	(279)
Total liabilities	8,701	8,055			474	456					8,538	7,878		(311)	(279)
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	782	781			782	781
Noncontrolling interest in consolidated entity - Exchange	6,061	5,512									6,061	5,512
Total equity	6,843	6,293		6,334	782	781		912			6,061	5,512	5,422
Total liabilities, shareholders' equity and noncontrolling interest	15,544	14,348			1,256	1,237					14,599	13,390		(311)	(279)
Note receivable from EFL, annual interest rate (as a percent)									6.70%
Interest income									$ 1.3	$ 1.3