Indemnity Supplemental Information (Details) (USD $) In Millions, unless otherwise specified									3 Months Ended
	Mar. 31, 2012	Dec. 31, 2011	Mar. 31, 2011	Dec. 31, 2010	Mar. 31, 2012 Indemnity	Dec. 31, 2011 Indemnity	Mar. 31, 2011 Indemnity	Dec. 31, 2010 Indemnity	Mar. 31, 2012 Indemnity Erie Family Life Insurance Company ("EFL")	Mar. 31, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Mar. 31, 2012 Exchange	Dec. 31, 2011 Exchange	Dec. 31, 2010 Exchange	Mar. 31, 2012 Reclassifications and eliminations	Dec. 31, 2011 Reclassifications and eliminations
Available-for-sale securities, at fair value:
Fixed maturities	$ 7,977	$ 7,840			$ 494	$ 548					$ 7,483	$ 7,292
Equity securities	647	589			26	25					621	564
Trading securities, at fair value	2,625	2,335			29	27					2,596	2,308
Limited partnerships	1,291	1,290			204	208					1,087	1,082
Other invested assets	20	20			1	1					19	19
Total investments	12,560	12,074			754	809					11,806	11,265
Cash and cash equivalents	199	185	211	430	28	11	86	310			171	174
Premiums receivable from policyholders	1,000	976									1,000	976
Reinsurance recoverable	167	166									167	166
Deferred income taxes	18	19			18	19
Deferred acquisition costs	482	487									482	487
Other assets	406	441			115	119					291	322
Receivables from the Exchange and other affiliates					256	254								(256)	(254)
Note receivable from EFL					25	25								(25)	(25)
Total assets	14,832	14,348			1,196	1,237					13,917	13,390		(281)	(279)
Liabilities
Losses and loss expense reserves	3,451	3,499									3,451	3,499
Life policy and deposit contract reserves	1,689	1,671									1,689	1,671
Unearned premiums	2,196	2,178									2,196	2,178
Deferred income taxes	279	147									279	147
Other liabilities, prior to consolidation eliminations	541	560			420	456					402	383		(281)	(279)
Total liabilities	8,156	8,055			420	456					8,017	7,878		(281)	(279)
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	776	781			776	781
Noncontrolling interest in consolidated entity - Exchange	5,900	5,512									5,900	5,512
Total equity	6,676	6,293		6,334	776	781		912			5,900	5,512	5,422
Total liabilities, shareholders' equity and noncontrolling interest	14,832	14,348			1,196	1,237					13,917	13,390		(281)	(279)
Note receivable from EFL, annual interest rate (as a percent)									6.70%
EFL accrued interest payable to Indemnity									$ 0.4	$ 0.4