Segment Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Revenues
Premiums earned/life policy revenue	$ 1,175	$ 1,087
Net investment income	103	108
Net realized investment gains	249	296
Net impairment losses recognized in earnings	0	0
Equity in earnings of limited partnerships	36	21
Service agreement and other revenue	8	8
Total revenues	1,571	1,520
Benefits and expenses
Insurance losses and loss expenses	842	716
Policy acquisition and underwriting expenses	293	270
Total benefits and expenses	1,135	986
Income (loss) from operations before income taxes and noncontrolling interest	436	534
Provision for income taxes	146	180
Net income (loss)	290	354	619
Management operations
Segment information
Indemnity's maximum management fee rate as a percent of premiums written and assumed by the Exchange (as a percent)	25.00%
Revenues
Management fee revenue	296	269
Service agreement and other revenue	7	7
Total revenues	303	276
Benefits and expenses
Cost of management operations	254	230
Total benefits and expenses	254	230
Income (loss) from operations before income taxes and noncontrolling interest	49	46
Provision for income taxes	17	16
Net income (loss)	32	30
Property and casualty insurance operations
Revenues
Premiums earned/life policy revenue	1,156	1,069
Total revenues	1,156	1,069
Benefits and expenses
Insurance losses and loss expenses	817	692
Policy acquisition and underwriting expenses	328	302
Total benefits and expenses	1,145	994
Income (loss) from operations before income taxes and noncontrolling interest	11	75
Provision for income taxes	4	26
Net income (loss)	7	49
Life insurance operations
Revenues
Premiums earned/life policy revenue	19	18
Service agreement and other revenue	1	1
Total revenues	20	19
Benefits and expenses
Insurance losses and loss expenses	26	25
Policy acquisition and underwriting expenses	9	9
Total benefits and expenses	35	34
Income (loss) from operations before income taxes and noncontrolling interest	(15)	(15)
Provision for income taxes	(5)	(5)
Net income (loss)	(10)	(10)
Investment operations
Revenues
Net investment income	106	111
Net realized investment gains	249	296
Net impairment losses recognized in earnings	0	0
Equity in earnings of limited partnerships	36	21
Total revenues	391	428
Benefits and expenses
Income (loss) from operations before income taxes and noncontrolling interest	391	428
Provision for income taxes	130	143
Net income (loss)	261	285
Eliminations
Revenues
Premiums earned/life policy revenue	0	0
Net investment income	(3)	(3)
Management fee revenue	(296)	(269)
Total revenues	(299)	(272)
Benefits and expenses
Cost of management operations	(254)	(230)
Insurance losses and loss expenses	(1)	(1)
Policy acquisition and underwriting expenses	(44)	(41)
Total benefits and expenses	(299)	(272)
Erie Family Life Insurance Company ("EFL") | Life insurance operations
Segment information
Total investment revenues	26	24
Benefits and expenses
Income (loss) from operations before income taxes and noncontrolling interest	$ 11	$ 9