Income Taxes (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended								12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Indemnity	Dec. 31, 2010 Indemnity	Dec. 31, 2009 Indemnity	Dec. 31, 2010 Indemnity Erie Family Life Insurance Company ("EFL")	Mar. 31, 2011 Indemnity Erie Family Life Insurance Company ("EFL")	Dec. 31, 2011 Exchange	Dec. 31, 2010 Exchange	Dec. 31, 2009 Exchange
Income taxes
Current income tax expense (benefit)				$ 85	$ 37	$ 56			$ 110	$ (43)	$ 7
Deferred income tax expense (benefit)	(105)	342	15	0	67	(7)			(105)	278	22
Provision for income taxes	90	339	78	85	104	49			5	235	29
Increase in Indemnity's deferred tax liability recorded for its investment in EFL as a result of a change in the tax rate used to calculate the liability							18
Indemnity's ownership interest in EFL sold to the Exchange (as a percent)								21.60%
Deduction available for dividends received (as a percent)							80.00%
Reconciliation of the provision for income taxes, with amounts determined by applying the statutory federal income tax rates to pre-tax income
Income tax at statutory rates				89	93	53			37	259	130
Tax-exempt interest				(3)	(3)	(3)			(15)	(16)	(17)
Dividends received deduction				(1)	(1)	(1)			(13)	(11)	(11)
Deferred tax valuation allowance				0	(2)	0			0	(4)	(71)
Erie Family Life (losses) earnings				(1)	15	0
Goodwill impairments									0	8	0
Prior year adjustments									(5)	0	0
Other, net				1	2	0			1	(1)	(2)
Provision for income taxes	$ 90	$ 339	$ 78	$ 85	$ 104	$ 49			$ 5	$ 235	$ 29
Indemnity's effective income tax rate on its share of EFL earnings, prior to decision to sell its ownership interest (as a percent)							7.00%
Indemnity's effective income tax rate on its share of EFL earnings, after decision to sell its ownership interest (as a percent)							35.00%