Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Segment Information
Threshold percentage for disclosure of revenue from a single customer or agent									10.00%
Revenues
Premiums earned/life policy revenue									$ 4,214	$ 3,987	$ 3,869
Net investment income									433	433	433
Net realized investment (losses) gains									(4)	313	412
Net impairment losses recognized in earnings									(2)	(6)	(126)
Equity in earnings (losses) of limited partnerships									149	128	(369)
Service agreement and other revenue									34	35	36
Total revenues	1,418	796	1,245	1,365	1,401	1,357	916	1,216	4,824	4,890	4,255
Benefits and expenses
Insurance losses and loss expenses									3,444	2,900	2,728
Policy acquisition and underwriting expenses									1,022	969	1,003
Goodwill impairment										22
Total benefits and expenses	993	1,101	1,419	953	984	952	967	988	4,466	3,891	3,731
Income (loss) before income taxes	425	(305)	(174)	412	417	405	(51)	228	358	999	524
Provision for income taxes									90	339	78
Net income (loss)	281	(180)	(107)	274	254	275	(31)	162	268	660	446
Management operations
Segment information
Indemnity's maximum management fee rate as a percent of premiums written and assumed by the Exchange									25.00%
Revenues
Management fee revenue									1,067	1,009	965
Service agreement and other revenue									33	34	35
Total revenues									1,100	1,043	1,000
Benefits and expenses
Cost of management operations									892	841	813
Total benefits and expenses									892	841	813
Income (loss) before income taxes									208	202	187
Provision for income taxes									73	71	60
Net income (loss)									135	131	127
Property and casualty insurance operations
Revenues
Premiums earned/life policy revenue									4,149	3,925	3,808
Total revenues									4,149	3,925	3,808
Benefits and expenses
Insurance losses and loss expenses									3,349	2,815	2,644
Policy acquisition and underwriting expenses									1,178	1,113	1,135
Total benefits and expenses									4,527	3,928	3,779
Income (loss) before income taxes									(378)	(3)	29
Provision for income taxes									(132)	(1)	10
Net income (loss)									(246)	(2)	19
Life insurance operations
Revenues
Premiums earned/life policy revenue									67	64	63
Service agreement and other revenue									1	1	1
Total revenues									68	65	64
Benefits and expenses
Insurance losses and loss expenses									100	90	89
Policy acquisition and underwriting expenses									27	32	28
Total benefits and expenses									127	122	117
Income (loss) before income taxes									(59)	(57)	(53)
Provision for income taxes									(21)	(20)	(19)
Net income (loss)									(38)	(37)	(34)
Investment operations
Revenues
Net investment income									444	444	444
Net realized investment (losses) gains									(4)	313	412
Net impairment losses recognized in earnings									(2)	(6)	(126)
Equity in earnings (losses) of limited partnerships									149	128	(369)
Total revenues									587	879	361
Benefits and expenses
Goodwill impairment										22
Total benefits and expenses										22
Income (loss) before income taxes									587	857	361
Provision for income taxes									170	289	27
Net income (loss)									417	568	334
Eliminations
Revenues
Premiums earned/life policy revenue									(2)	(2)	(2)
Net investment income									(11)	(11)	(11)
Management fee revenue									(1,067)	(1,009)	(965)
Total revenues									(1,080)	(1,022)	(978)
Benefits and expenses
Cost of management operations									(892)	(841)	(813)
Insurance losses and loss expenses									(5)	(5)	(5)
Policy acquisition and underwriting expenses									(183)	(176)	(160)
Total benefits and expenses									(1,080)	(1,022)	(978)
Erie Family Life Insurance Company ("EFL")
Benefits and expenses
Income (loss) before income taxes									50	50	10
Erie Family Life Insurance Company ("EFL") | Investment operations
Segment information
Total investment revenues									$ 109	$ 107	$ 63