Indemnity Supplemental Information (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Available-for-sale securities, at fair value:
Fixed maturities	$ 9,933.0		$ 9,571.0
Equity securities	839.0		875.0
Trading securities, at fair value	3,144.0		3,223.0
Limited partnerships	943.0		979.0
Other invested assets	22.0		21.0
Total investments	14,881.0		14,669.0
Cash and cash equivalents	421.0	$ 300.0	514.0	$ 452.0
Premiums receivable from policyholders	1,384.0		1,281.0
Reinsurance recoverable	162.0		161.0
Deferred income tax asset	44.0		37.0
Deferred acquisition costs	635.0		595.0
Other assets	542.0		501.0
Total assets	18,069.0		17,758.0
Liabilities
Losses and loss expense reserves	3,963.0		3,853.0
Life policy and deposit contract reserves	1,837.0		1,812.0
Unearned premiums	3,007.0		2,834.0
Deferred income tax liability	413.0		490.0
Other liabilities, adjusted for consolidation presentation	687.0		786.0
Total liabilities	9,907.0		9,775.0
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	732.0		703.0
Noncontrolling interest in consolidated entity - Exchange	7,430.0		7,280.0
Total equity	8,162.0		7,983.0	7,550.0
Total liabilities, shareholders' equity, and noncontrolling interest	18,069.0		17,758.0
Indemnity
Available-for-sale securities, at fair value:
Fixed maturities	561.0		564.0
Equity securities	22.0		25.0
Limited partnerships	101.0		113.0
Other invested assets	1.0		1.0
Total investments	685.0		703.0
Cash and cash equivalents	77.0	63.0	92.0	49.0
Deferred income tax asset	44.0		37.0
Other assets	123.0		127.0
Receivables from the Exchange and other affiliates	369.0		335.0
Note receivable from EFL	25.0		25.0
Total assets	1,323.0		1,319.0
Liabilities
Other liabilities, adjusted for consolidation presentation	591.0		616.0
Total liabilities	591.0		616.0
Shareholders' equity and noncontrolling interest
Total Indemnity shareholders' equity	732.0		703.0
Total equity	732.0		703.0	734.0
Total liabilities, shareholders' equity, and noncontrolling interest	1,323.0		1,319.0
Exchange
Available-for-sale securities, at fair value:
Fixed maturities	9,372.0		9,007.0
Equity securities	817.0		850.0
Trading securities, at fair value	3,144.0		3,223.0
Limited partnerships	842.0		866.0
Other invested assets	21.0		20.0
Total investments	14,196.0		13,966.0
Cash and cash equivalents	344.0		422.0
Premiums receivable from policyholders	1,384.0		1,281.0
Reinsurance recoverable	162.0		161.0
Deferred acquisition costs	635.0		595.0
Other assets	419.0		374.0
Total assets	17,140.0		16,799.0
Liabilities
Losses and loss expense reserves	3,963.0		3,853.0
Life policy and deposit contract reserves	1,837.0		1,812.0
Unearned premiums	3,007.0		2,834.0
Deferred income tax liability	413.0		490.0
Other liabilities, adjusted for consolidation presentation	490.0		530.0
Total liabilities	9,710.0		9,519.0
Shareholders' equity and noncontrolling interest
Noncontrolling interest in consolidated entity - Exchange	7,430.0		7,280.0
Total equity	7,430.0		7,280.0	$ 6,816.0
Total liabilities, shareholders' equity, and noncontrolling interest	17,140.0		16,799.0
Payable to Indemnity	365.0		331.0
Erie Family Life Insurance Company (EFL)
Available-for-sale securities, at fair value:
Note receivable from EFL	25.0
Shareholders' equity and noncontrolling interest
Payable to Indemnity	$ 4.0		4.0
Note receivable from EFL, annual interest rate (as a percent)	6.70%
Note receivable from EFL, interest income recognized by Indemnity	$ 0.8	$ 0.8
Reclassifications and eliminations
Available-for-sale securities, at fair value:
Receivables from the Exchange and other affiliates	(369.0)		(335.0)
Note receivable from EFL	(25.0)		(25.0)
Total assets	(394.0)		(360.0)
Liabilities
Other liabilities, adjusted for consolidation presentation	(394.0)		(360.0)
Total liabilities	(394.0)		(360.0)
Shareholders' equity and noncontrolling interest
Total liabilities, shareholders' equity, and noncontrolling interest	$ (394.0)		$ (360.0)