Indemnity Supplemental Information (Details) (USD $) In Millions, unless otherwise specified									9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2013 Indemnity	Dec. 31, 2012 Indemnity	Sep. 30, 2012 Indemnity	Dec. 31, 2011 Indemnity	Sep. 30, 2013 Indemnity Erie Family Life Insurance Company (EFL)	Sep. 30, 2012 Indemnity Erie Family Life Insurance Company (EFL)	Dec. 31, 2012 Indemnity Erie Family Life Insurance Company (EFL)	Sep. 30, 2013 Exchange	Dec. 31, 2012 Exchange	Dec. 31, 2011 Exchange	Sep. 30, 2013 Reclassifications and eliminations	Dec. 31, 2012 Reclassifications and eliminations
Available-for-sale securities, at fair value:
Fixed maturities	$ 8,420	$ 8,159			$ 499	$ 452						$ 7,921	$ 7,707
Equity securities	897	1,000			48	55						849	945
Trading securities, at fair value	2,945	2,417			0	0						2,945	2,417
Limited partnerships	1,137	1,217			158	180						979	1,037
Other invested assets	21	21			1	1						20	20
Total investments	13,420	12,814			706	688						12,714	12,126
Cash and cash equivalents	535	400	404	185	33	12	12	11				502	388
Premiums receivable from policyholders	1,203	1,062										1,203	1,062
Reinsurance recoverable	174	168										174	168
Net deferred income tax asset	42	37			42	37						0	0
Deferred acquisition costs	574	504										574	504
Other assets	436	456			107	117						329	339
Receivables from the Exchange and other affiliates					320	281			3		3				(320)	(281)
Note receivable from EFL					25	25			25						(25)	(25)
Total assets	16,384	15,441			1,233	1,160						15,496	14,587		(345)	(306)
Liabilities
Losses and loss expense reserves	3,712	3,598										3,712	3,598
Life policy and deposit contract reserves	1,754	1,708										1,754	1,708
Unearned premiums	2,654	2,365										2,654	2,365
Net deferred income tax liability	368	365			0	0						368	365
Other liabilities, adjusted for consolidation presentation	697	614			576	518						466	402		(345)	(306)
Total liabilities	9,185	8,650			576	518						8,954	8,438		(345)	(306)
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	657	642			657	642
Noncontrolling interest in consolidated entity - Exchange	6,542	6,149										6,542	6,149
Total equity	7,199	6,791		6,293	657	642		781				6,542	6,149	5,512
Total liabilities, shareholders' equity and noncontrolling interest	16,384	15,441			1,233	1,160						15,496	14,587		(345)	(306)
Recievables from the Exchange					317	278
Note receivable from EFL, annual interest rate (as a percent)									6.70%
Note receivable from EFL, interest income recognized by Indemnity									$ 1.3	$ 1.3