Supplemental Compensation Plans, Assumptions Used to Determine Benefit Obligations (Details) - Pension Plan [Member]	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Salary Continuation Plan [Member]
Assumptions used to determine benefit obligations [Abstract]
Discount rate used to determine net periodic benefit cost for years ended	4.10%	3.40%	3.80%
Discount rate used to determine benefit obligations	3.00%	4.10%	3.40%
Future salary increases	5.70%	5.70%	5.20%
Directors' Retirement Plan [Member]
Assumptions used to determine benefit obligations [Abstract]
Discount rate used to determine net periodic benefit cost for years ended	3.70%	3.00%	3.30%
Discount rate used to determine benefit obligations	2.40%	3.70%	3.00%