Employee Benefit Plans - Supplemental Non-qualified Unfunded Plans - Narrative (Details) - Other postretirement benefits - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net periodic pension cost, Discount rate (as a percent)	3.19%	4.33%	3.65%
Officers and Key Employees
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Net periodic pension cost, Discount rate (as a percent)	2.87%	2.86%	2.16%
Amount accrued	$ 0.4	$ 0.5