Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended	9 Months Ended	3 Months Ended			9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Sep. 30, 2012 Management operations	Sep. 30, 2013 Operating segment Management operations	Sep. 30, 2012 Operating segment Management operations	Jun. 30, 2012 Operating segment Management operations	Sep. 30, 2013 Operating segment Management operations	Sep. 30, 2012 Operating segment Management operations	Sep. 30, 2013 Operating segment Property and casualty insurance operations	Sep. 30, 2012 Operating segment Property and casualty insurance operations	Sep. 30, 2013 Operating segment Property and casualty insurance operations	Sep. 30, 2012 Operating segment Property and casualty insurance operations	Sep. 30, 2013 Operating segment Life insurance operations	Sep. 30, 2012 Operating segment Life insurance operations	Sep. 30, 2013 Operating segment Life insurance operations	Sep. 30, 2012 Operating segment Life insurance operations	Sep. 30, 2013 Operating segment Life insurance operations Erie Family Life Insurance Company (EFL)	Sep. 30, 2012 Operating segment Life insurance operations Erie Family Life Insurance Company (EFL)	Sep. 30, 2013 Operating segment Life insurance operations Erie Family Life Insurance Company (EFL)	Sep. 30, 2012 Operating segment Life insurance operations Erie Family Life Insurance Company (EFL)	Sep. 30, 2013 Operating segment Investment operations	Sep. 30, 2012 Operating segment Investment operations	Sep. 30, 2013 Operating segment Investment operations	Sep. 30, 2012 Operating segment Investment operations	Sep. 30, 2013 Eliminations	Sep. 30, 2012 Eliminations	Sep. 30, 2013 Eliminations	Sep. 30, 2012 Eliminations
Segment information
Indemnity's maximum management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)										25.00%
Reduction in commission expense due to adjustment						$ 6			$ 6
Indemnity commission expense adjustment description										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 which was incorrectly recorded as a benefit to the Exchange in prior periods.
Total investment revenues																				26	25	78	77
Revenues
Premiums earned/life policy revenue	1,241	1,137	3,631	3,333								1,221	1,118	3,573	3,279	21	19	60	55									(1)	0	(2)	(1)
Net investment income	109	105	316	326																				111	108	324	334	(2)	(3)	(8)	(8)
Net realized investment gains (losses)	191	169	501	358																				191	169	501	358
Net impairment losses recognized in earnings	(9)	0	(10)	0																				(9)	0	(10)	0
Equity in earnings of limited partnerships	37	41	112	99																				37	41	112	99
Management fee revenue							333	305		965	882																	(333)	(305)	(965)	(882)
Service agreement and other revenue	8	8	24	24			8	8		23	23					0	0	1	1
Total revenues	1,577	1,460	4,574	4,140			341	313		988	905	1,221	1,118	3,573	3,279	21	19	61	56					330	318	927	791	(336)	(308)	(975)	(891)
Benefits and expenses
Cost of management operations							281	247		820	734																	(281)	(247)	(820)	(734)
Insurance losses and loss expenses	868	912	2,571	2,571								841	890	2,495	2,501	28	24	80	74									(1)	(2)	(4)	(4)
Policy acquisition and underwriting expenses	311	278	906	835								356	329	1,032	963	9	8	25	25									(54)	(59)	(151)	(153)
Total benefits and expenses	1,179	1,190	3,477	3,406			281	247		820	734	1,197	1,219	3,527	3,464	37	32	105	99									(336)	(308)	(975)	(891)
Income (loss) from operations before income taxes and noncontrolling interest	398	270	1,097	734			60	66		168	171	24	(101)	46	(185)	(16)	(13)	(44)	(43)	10	12	34	34	330	318	927	791
Provision for income taxes	131	86	363	234			21	23		59	60	8	(36)	16	(65)	(5)	(4)	(15)	(15)					107	103	303	254
Net income (loss)	$ 267	$ 184	$ 734	$ 500	$ 619		$ 39	$ 43		$ 109	$ 111	$ 16	$ (65)	$ 30	$ (120)	$ (11)	$ (9)	$ (29)	$ (28)					$ 223	$ 215	$ 624	$ 537