Deferred Policy Acquisition Costs (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Components of the Property and Casualty Group's and EFL's deferred policy acquisition costs assets
Deferred policy acquisition costs asset at beginning of year	$ 467
Amortized deferred policy acquisition costs	(680)	(652)	(624)
Deferred policy acquisition costs asset at end of year	487	467
Erie Family Life Insurance Company ("EFL")
Components of the Property and Casualty Group's and EFL's deferred policy acquisition costs assets
Deferred policy acquisition costs asset at beginning of year	140	154
Capitalized deferred policy acquisition costs	18	17
Amortized deferred policy acquisition costs	(12)	(16)
Amortized shadow deferred policy acquisition costs	(2)	(15)
Deferred policy acquisition costs asset at end of year	144	140
Property and Casualty Group
Components of the Property and Casualty Group's and EFL's deferred policy acquisition costs assets
Deferred policy acquisition costs asset at beginning of year	327	313
Capitalized deferred policy acquisition costs	684	649
Amortized deferred policy acquisition costs	(668)	(635)
Deferred policy acquisition costs asset at end of year	$ 343	$ 327