Leases - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 13.1	$ 14.0
Erie Insurance Exchange
Lessee, Lease, Description [Line Items]
Operating lease costs, amount reimbursed from exchange and its subsidiaries	5.3	$ 6.0
Erie Insurance Exchange | Office Space
Lessee, Lease, Description [Line Items]
Operating lease assets	$ 6.3