Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2010
Revenues
Premiums earned/life policy revenue	$ 1,109	$ 1,047	$ 2,196	$ 2,077
Net investment income	113	113	221	218
Net realized investment gains (losses)	(107)	39	189	188
Net impairment losses recognized in earnings	0	0	0	0
Equity in earnings of limited partnerships	37	38	58	110
Service agreement and other revenue	8	8	16	17
Total revenues	1,160	1,245	2,680	2,610
Benefits and expenses
Insurance losses and loss expenses	943	1,170	1,659	1,876
Policy acquisition and underwriting expenses	287	249	557	496
Total benefits and expenses	1,230	1,419	2,216	2,372
Income (loss) before income taxes	(70)	(174)	464	238
Provision for income taxes	(32)	(67)	148	71
Net (loss) income	(38)	(107)	316	167	268
Management operations
Segment information
Indemnity's maximum management fee rate as a percent of premiums written and assumed by the Exchange			25.00%
Reduction in commission expense due to adjustment	6.0		6.0		0.5	0.7
Indemnity commission expense adjustment	This amount represents the reimbursement by the North Carolina Reinsurance Facility (NCRF) for commissions Indemnity paid to agents on the surcharges collected on behalf of the NCRF in prior periods. This amount was incorrectly recorded as a benefit to the Exchange in prior periods.
Revenues
Management fee revenue	308	285	577	536
Service agreement and other revenue	8	9	15	17
Total revenues	316	294	592	553
Benefits and expenses
Cost of management operations	257	230	487	441
Total benefits and expenses	257	230	487	441
Income (loss) before income taxes	59	64	105	112
Provision for income taxes	21	22	37	39
Net (loss) income	38	42	68	73
Property and casualty insurance operations
Revenues
Premiums earned/life policy revenue	1,092	1,030	2,161	2,044
Total revenues	1,092	1,030	2,161	2,044
Benefits and expenses
Insurance losses and loss expenses	919	1,147	1,611	1,830
Policy acquisition and underwriting expenses	332	298	634	580
Total benefits and expenses	1,251	1,445	2,245	2,410
Income (loss) before income taxes	(159)	(415)	(84)	(366)
Provision for income taxes	(55)	(145)	(29)	(128)
Net (loss) income	(104)	(270)	(55)	(238)
Life insurance operations
Revenues
Premiums earned/life policy revenue	18	18	36	34
Service agreement and other revenue	0	(1)	1	0
Total revenues	18	17	37	34
Benefits and expenses
Insurance losses and loss expenses	25	25	50	49
Policy acquisition and underwriting expenses	8	7	17	14
Total benefits and expenses	33	32	67	63
Income (loss) before income taxes	(15)	(15)	(30)	(29)
Provision for income taxes	(6)	(5)	(11)	(10)
Net (loss) income	(9)	(10)	(19)	(19)
Investment operations
Revenues
Net investment income	115	115	226	223
Net realized investment gains (losses)	(107)	39	189	188
Net impairment losses recognized in earnings	0	0	0	0
Equity in earnings of limited partnerships	37	38	58	110
Total revenues	45	192	473	521
Benefits and expenses
Income (loss) before income taxes	45	192	473	521
Provision for income taxes	8	61	151	170
Net (loss) income	37	131	322	351
Eliminations
Revenues
Premiums earned/life policy revenue	(1)	(1)	(1)	(1)
Net investment income	(2)	(2)	(5)	(5)
Management fee revenue	(308)	(285)	(577)	(536)
Total revenues	(311)	(288)	(583)	(542)
Benefits and expenses
Cost of management operations	(257)	(230)	(487)	(441)
Insurance losses and loss expenses	(1)	(2)	(2)	(3)
Policy acquisition and underwriting expenses	(53)	(56)	(94)	(98)
Total benefits and expenses	(311)	(288)	(583)	(542)
Erie Family Life Insurance Company ("EFL") | Life insurance operations
Segment information
Total investment revenues	28	27	52	54
Benefits and expenses
Income (loss) before income taxes	$ 13	$ 12	$ 22	$ 25