Maximum percentage of employee compensation the employee may defer under a deferred compensation plan of the Company.

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Represents the percentage at which incentive plan costs are reimbursed to the parent company.

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Represents the Company's number of deferred compensation plans for directors.

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Represents the Company's number of deferred compensation plans for executives, senior vice presidents and other selected officers.

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Represents the Company's number of incentive plans for executives, senior vice presidents and other selected officers.

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Period over which vested share credits will be paid upon separation from service.

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The maximum number of shares that may be earned by any single participant during any specified period, which may be a specified performance period or calendar year, net of any subsequent amendments and adjustments, for awards under the equity-based compensation plan.

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Amount of cash paid to settle liability for award under share-based payment arrangement.

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Number of shares authorized for issuance under share-based payment arrangement.

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Per share weighted-average price paid for shares purchased on open market for issuance under share-based payment arrangement.

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Number of shares purchased for issuance under share-based payment arrangement.

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Incentive and Deferred Compensation Plans - Narrative (Details)	1 Months Ended			9 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2018 USD ($)	Jun. 30, 2017 USD ($) $ / shares shares	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($) Plans $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) $ / shares shares
Incentive and deferred compensation plans
Number of incentive plans for executives, senior vice presidents and other selected officers \| Plans					2
Number of deferred compensation plans for executives, senior vice presidents and other selected officers \| Plans					2
Number of deferred compensation plans for outside directors \| Plans					2
Annual incentive plan awards
Incentive and deferred compensation plans
Maximum percentage of employee compensation that can be deferred (percentage)					100.00%
Long-term incentive plan awards
Incentive and deferred compensation plans
Maximum percentage of employee compensation that can be deferred (percentage)					100.00%
Vesting period of performance and/or service condition(s)					3 years
Maximum dollar amount which may be received by any single participant during any specified period					$ 5,000,000
Compensation cost related to share-based compensation plan awards					7,300,000	$ 6,300,000	$ 10,300,000
Tax benefits recognized in income related to award expense					1,500,000	1,300,000	3,600,000
Total unrecognized compensation cost related to share-based compensation plan awards pertaining to open performance periods					$ 4,900,000
Expected period of recognition related to unrecognized compensation cost					2 years
Long-term incentive plan awards \| Class A Common Stock
Incentive and deferred compensation plans
Maximum number of shares authorized for grant (in shares) \| shares					1,500,000
Maximum number of shares which may be received by any single participant during any specified period (in shares) \| shares					250,000
Long-term incentive plan awards \| Performance Period Long-Term Incentive Plan 2017-2019
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards				$ 7,800,000
Long-term incentive plan awards \| Performance Period Long Term Incentive Plan 2016-2018
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards	$ 8,200,000
Long-term incentive plan awards \| Performance Period Long-Term Incentive Plan 2015-2017
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards		$ 8,300,000
Long-term incentive plan awards \| Performance Period Long Term Incentive Plan 2014-2016
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards			$ 4,700,000
Long-term incentive plan awards \| Performance Period Long Term Incentive Plan 2014-2016 \| Class A Common Stock
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share) \| $ / shares			$ 122.40
Total cost of shares purchased for share-based compensation awards			$ 5,700,000
Long-term incentive plan awards \| Performance Period Long Term Incentive Plan 2014-2016 \| Class A Common Stock \| Performance shares
Incentive and deferred compensation plans
Shares purchased for share-based compensation awards (in shares) \| shares			46,884
Incentive compensation deferral plan
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards					$ 500,000	$ 700,000	1,400,000
Incentive compensation deferral plan \| Class A Common Stock
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share) \| $ / shares					$ 176.34	$ 119.28
Total cost of shares purchased for share-based compensation awards					$ 800,000	$ 1,400,000
Vesting percent of the grant in Class A common stock (percentage)					100.00%
Payment period for vested share credits					3 years
Incentive compensation deferral plan \| Class A Common Stock \| Performance shares
Incentive and deferred compensation plans
Shares purchased for share-based compensation awards (in shares) \| shares					4,387	12,005
Stock compensation plan for outside directors
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards					$ 1,100,000	$ 800,000	$ 900,000
Stock compensation plan for outside directors \| Class A Common Stock
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share) \| $ / shares					$ 194.62	$ 122.19	$ 121.85
Total cost of shares purchased for share-based compensation awards					$ 1,400,000	$ 1,100,000	$ 1,200,000
Stock compensation plan for outside directors \| Class A Common Stock \| Performance shares
Incentive and deferred compensation plans
Shares purchased for share-based compensation awards (in shares) \| shares					7,370	9,285	9,663
Stock compensation plan for outside directors \| Three Month Vesting Period \| Class A Common Stock
Incentive and deferred compensation plans
Vesting period of performance and/or service condition(s)					3 months
Vesting percent of the grant in Class A common stock (percentage)					25.00%
Equity compensation plan
Incentive and deferred compensation plans
Compensation cost related to share-based compensation plan awards					$ 500,000	$ 400,000	$ 200,000
Total unrecognized compensation cost related to share-based compensation plan awards pertaining to open performance periods					$ 400,000
Expected period of recognition related to unrecognized compensation cost					3 years
Equity compensation plan \| Class A Common Stock
Incentive and deferred compensation plans
Maximum number of shares authorized for grant (in shares) \| shares					100,000
Maximum number of shares which may be received by any single participant during any specified period (in shares) \| shares					5,000
Equity compensation plan \| Performance Period Equity Compensation Plan 2016 \| Class A Common Stock
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share) \| $ / shares					$ 132.35
Total cost of shares purchased for share-based compensation awards					$ 400,000
Equity compensation plan \| Performance Period Equity Compensation Plan 2016 \| Class A Common Stock \| Performance shares
Incentive and deferred compensation plans
Shares purchased for share-based compensation awards (in shares) \| shares					3,246
Equity compensation plan \| Performance Period Equity Compensation Plan 2014-2015 \| Class A Common Stock
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share) \| $ / shares						$ 117.39
Total cost of shares purchased for share-based compensation awards						$ 700,000
Equity compensation plan \| Performance Period Equity Compensation Plan 2014-2015 \| Class A Common Stock \| Performance shares
Incentive and deferred compensation plans
Shares purchased for share-based compensation awards (in shares) \| shares						5,830
Equity compensation plan \| Performance Period Equity Compensation Plan 2014 \| Class A Common Stock
Incentive and deferred compensation plans
Average price per share for shares purchased (in dollars per share) \| $ / shares							$ 111.55
Total cost of shares purchased for share-based compensation awards							$ 400,000
Equity compensation plan \| Performance Period Equity Compensation Plan 2014 \| Class A Common Stock \| Performance shares
Incentive and deferred compensation plans
Shares purchased for share-based compensation awards (in shares) \| shares							3,785
Erie Insurance Exchange (EIE) \| Long-term incentive plan awards
Incentive and deferred compensation plans
Incentive plan compensation cost reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)					47.00%
Erie Insurance Exchange (EIE) \| Incentive compensation deferral plan
Incentive and deferred compensation plans
Incentive plan compensation cost reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)					42.00%
Erie Insurance Exchange (EIE) \| Equity compensation plan
Incentive and deferred compensation plans
Incentive plan compensation cost reimbursed to Indemnity from the Exchange and its subsidiaries (as a percent)					49.00%	68.00%	38.00%