Pension Plans - Qualified Plan - Weighted-Average Assumptions Used in Determining Net Periodic Pension Expense (Details) - Pension Plan [Member] - Qualified Plan [Member]	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Discount rate (as a percent)	2.40%	3.51%	3.47%
Rate of compensation increase	0.00%	0.00%	0.00%
Expected long-term rate of return on plan assets	6.50%	6.50%	6.50%