Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues
Premiums earned/life policy revenue									$ 4,493	$ 4,214	$ 3,987
Net investment income									438	433	433
Net realized investment gains (losses)									418	(4)	313
Net impairment losses recognized in earnings									0	(2)	(6)
Equity in earnings of limited partnerships									131	149	128
Management fee revenue
Service agreement and other revenue									32	34	35
Total revenues	1,372	1,460	1,160	1,520	1,418	796	1,245	1,365	5,512	4,824	4,890
Benefits and expenses
Cost of management operations
Insurance losses and loss expenses									3,480	3,444	2,900
Policy acquisition and underwriting expenses									1,133	1,022	969
Goodwill impairment											22
Total benefits and expenses	1,207	1,190	1,230	986	993	1,101	1,419	953	4,613	4,466	3,891
Income (loss) from operations before income taxes and noncontrolling interest	165	270	(70)	534	425	(305)	(174)	412	899	358	999
Provision for income taxes									280	90	339
Net income (loss)	119	184	(38)	354	281	(180)	(107)	274	619	268	660
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	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									1,157	1,067	1,009
Service agreement and other revenue									31	33	34
Total revenues									1,188	1,100	1,043
Benefits and expenses
Cost of management operations									983	892	841
Total benefits and expenses									983	892	841
Income (loss) from operations before income taxes and noncontrolling interest									205	208	202
Provision for income taxes									72	73	71
Net income (loss)									133	135	131
Property and casualty insurance operations
Revenues
Premiums earned/life policy revenue									4,422	4,149	3,925
Total revenues									4,422	4,149	3,925
Benefits and expenses
Insurance losses and loss expenses									3,384	3,349	2,815
Policy acquisition and underwriting expenses									1,284	1,178	1,113
Total benefits and expenses									4,668	4,527	3,928
Income (loss) from operations before income taxes and noncontrolling interest									(246)	(378)	(3)
Provision for income taxes									(86)	(132)	(1)
Net income (loss)									(160)	(246)	(2)
Life insurance operations
Revenues
Premiums earned/life policy revenue									73	67	64
Service agreement and other revenue									1	1	1
Total revenues									74	68	65
Benefits and expenses
Insurance losses and loss expenses									101	100	90
Policy acquisition and underwriting expenses									31	27	32
Total benefits and expenses									132	127	122
Income (loss) from operations before income taxes and noncontrolling interest									(58)	(59)	(57)
Provision for income taxes									(20)	(21)	(20)
Net income (loss)									(38)	(38)	(37)
Investment operations
Revenues
Net investment income									449	444	444
Net realized investment gains (losses)									418	(4)	313
Net impairment losses recognized in earnings									0	(2)	(6)
Equity in earnings of limited partnerships									131	149	128
Total revenues									998	587	879
Benefits and expenses
Goodwill impairment											22
Total benefits and expenses											22
Income (loss) from operations before income taxes and noncontrolling interest									998	587	857
Provision for income taxes									314	170	289
Net income (loss)									684	417	568
Eliminations
Revenues
Premiums earned/life policy revenue									(2)	(2)	(2)
Net investment income									(11)	(11)	(11)
Management fee revenue									(1,157)	(1,067)	(1,009)
Total revenues									(1,170)	(1,080)	(1,022)
Benefits and expenses
Cost of management operations									(983)	(892)	(841)
Insurance losses and loss expenses									(5)	(5)	(5)
Policy acquisition and underwriting expenses									(182)	(183)	(176)
Total benefits and expenses									(1,170)	(1,080)	(1,022)
Income (loss) from operations before income taxes and noncontrolling interest
Provision for income taxes
Net income (loss)
Erie Family Life Insurance Company (EFL) | Life insurance operations
Segment information
Total investment revenues									104	109	107
Benefits and expenses
Income (loss) from operations before income taxes and noncontrolling interest									$ 46	$ 50	$ 50