Indemnity Supplemental Information (Details) (USD $) In Millions, unless otherwise specified									6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2013 Indemnity	Dec. 31, 2012 Indemnity	Jun. 30, 2012 Indemnity	Dec. 31, 2011 Indemnity	Jun. 30, 2013 Indemnity Erie Family Life Insurance Company ("EFL")	Jun. 30, 2012 Indemnity Erie Family Life Insurance Company ("EFL")	Dec. 31, 2012 Indemnity Erie Family Life Insurance Company ("EFL")	Jun. 30, 2013 Exchange	Dec. 31, 2012 Exchange	Dec. 31, 2011 Exchange	Jun. 30, 2013 Reclassifications and eliminations	Dec. 31, 2012 Reclassifications and eliminations
Available-for-sale securities, at fair value:
Fixed maturities	$ 8,163	$ 8,159			$ 438	$ 452						$ 7,725	$ 7,707
Equity securities	1,017	1,000			48	55						969	945
Trading securities, at fair value	2,724	2,417			0	0						2,724	2,417
Limited partnerships	1,177	1,217			166	180						1,011	1,037
Other invested assets	21	21			1	1						20	20
Total investments	13,102	12,814			653	688						12,449	12,126
Cash and cash equivalents	365	400	240	185	39	12	13	11				326	388
Premiums receivable from policyholders	1,191	1,062										1,191	1,062
Reinsurance recoverable	174	168										174	168
Net deferred income tax asset	43	37			43	37						0	0
Deferred acquisition costs	553	504										553	504
Other assets	451	456			115	117						336	339
Receivables from the Exchange and other affiliates					309	281			4		3				(309)	(281)
Note receivable from EFL					25	25									(25)	(25)
Total assets	15,879	15,441			1,184	1,160						15,029	14,587		(334)	(306)
Liabilities
Losses and loss expense reserves	3,668	3,598										3,668	3,598
Life policy and deposit contract reserves	1,739	1,708										1,739	1,708
Unearned premiums	2,553	2,365										2,553	2,365
Net deferred income tax liability	312	365			0	0						312	365
Other liabilities, adjusted for consolidation presentation	639	614			537	518						436	402		(334)	(306)
Total liabilities	8,911	8,650			537	518						8,708	8,438		(334)	(306)
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	647	642			647	642
Noncontrolling interest in consolidated entity - Exchange	6,321	6,149										6,321	6,149
Total equity	6,968	6,791		6,293	647	642		781				6,321	6,149	5,512
Total liabilities, shareholders' equity and noncontrolling interest	15,879	15,441			1,184	1,160						15,029	14,587		(334)	(306)
Recievables from the Exchange					305	278
Note receivable from EFL, annual interest rate (as a percent)									6.70%
Note receivable from EFL, interest income recognized by Indemnity									$ 0.8	$ 0.8