Employee Retirement Benefits (Weighted-Average Assumptions Used) (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Plan
Weighted average assumptions used to determine benefit obligations
Benefit obligation discount rate	2.68%	3.40%
Summary of the weighted average assumtions used to determine net periodic benefit cost
Discount rate	3.40%	4.34%	3.73%
Expected return on plan assets	7.00%	7.00%	7.25%
Pension Plan | Minimum
Weighted average assumptions used to determine benefit obligations
Benefit obligation rate of compensation increase	2.25%	2.25%
Summary of the weighted average assumtions used to determine net periodic benefit cost
Rate of compensation increase	2.25%	2.25%	2.75%
Pension Plan | Maximum
Weighted average assumptions used to determine benefit obligations
Benefit obligation rate of compensation increase	3.25%	3.25%
Summary of the weighted average assumtions used to determine net periodic benefit cost
Rate of compensation increase	3.25%	3.25%	3.25%
Supplemental Employee Retirement Plan
Weighted average assumptions used to determine benefit obligations
Benefit obligation discount rate	2.52%	3.33%
Summary of the weighted average assumtions used to determine net periodic benefit cost
Discount rate	3.33%	4.25%	3.61%
Supplemental Employee Retirement Plan | Minimum
Weighted average assumptions used to determine benefit obligations
Benefit obligation rate of compensation increase	2.25%	2.25%
Summary of the weighted average assumtions used to determine net periodic benefit cost
Rate of compensation increase	2.25%	2.25%	2.75%
Supplemental Employee Retirement Plan | Maximum
Weighted average assumptions used to determine benefit obligations
Benefit obligation rate of compensation increase	3.25%	3.25%
Summary of the weighted average assumtions used to determine net periodic benefit cost
Rate of compensation increase	3.25%	3.25%	3.25%