Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Segment Information
Threshold percentage for disclosure of revenue from a single customer or agent	10.00%
Revenues
Premiums earned/life policy revenue	$ 1,087	$ 1,030
Net investment income	108	105
Net realized investment gains	296	149
Net impairment losses recognized in earnings	0	0
Equity in earnings of limited partnerships	21	72
Service agreement and other revenue	8	9
Total revenues	1,520	1,365
Benefits and expenses
Insurance losses and loss expenses	716	706
Policy acquisition and underwriting expenses	270	247
Total benefits and expenses	986	953
Income (loss) before income taxes	534	412
Provision for income taxes	180	138
Net income (loss)	354	274	268
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	269	251
Service agreement and other revenue	7	8
Total revenues	276	259
Benefits and expenses
Cost of management operations	230	211
Total benefits and expenses	230	211
Income (loss) before income taxes	46	48
Provision for income taxes	16	17
Net income (loss)	30	31
Property and casualty insurance operations
Revenues
Premiums earned/life policy revenue	1,069	1,014
Total revenues	1,069	1,014
Benefits and expenses
Insurance losses and loss expenses	692	683
Policy acquisition and underwriting expenses	302	282
Total benefits and expenses	994	965
Income (loss) before income taxes	75	49
Provision for income taxes	26	17
Net income (loss)	49	32
Life insurance operations
Revenues
Premiums earned/life policy revenue	18	16
Service agreement and other revenue	1	1
Total revenues	19	17
Benefits and expenses
Insurance losses and loss expenses	25	24
Policy acquisition and underwriting expenses	9	7
Total benefits and expenses	34	31
Income (loss) before income taxes	(15)	(14)
Provision for income taxes	(5)	(5)
Net income (loss)	(10)	(9)
Investment operations
Revenues
Net investment income	111	108
Net realized investment gains	296	149
Net impairment losses recognized in earnings	0	0
Equity in earnings of limited partnerships	21	72
Total revenues	428	329
Benefits and expenses
Income (loss) before income taxes	428	329
Provision for income taxes	143	109
Net income (loss)	285	220
Eliminations
Revenues
Premiums earned/life policy revenue	0	0
Net investment income	(3)	(3)
Management fee revenue	(269)	(251)
Total revenues	(272)	(254)
Benefits and expenses
Cost of management operations	(230)	(211)
Insurance losses and loss expenses	(1)	(1)
Policy acquisition and underwriting expenses	(41)	(42)
Total benefits and expenses	(272)	(254)
Erie Family Life Insurance Company ("EFL") | Life insurance operations
Segment information
Total investment revenues	24	27
Benefits and expenses
Income (loss) before income taxes	$ 9	$ 13