Leases - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2019 USD ($)
Lessee, Lease, Description [Line Items]
Operating lease costs	$ 14.0
Erie Insurance Exchange
Lessee, Lease, Description [Line Items]
Operating lease costs, amount reimbursed from Exchange and its subsidiaries	6.0
Erie Insurance Exchange | Office Space
Lessee, Lease, Description [Line Items]
Operating lease assets	$ 11.7