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Postretirement Benefit Plans (Assumptions Used) (Details)
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Defined Benefit Postretirement Health And Life Coverage [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate 4.00% 3.50%  
Defined benefit plan, assumptions used calculating benefit obligation, Rate of compensation increase 3.00% 2.50%  
Defined benefit plan, assumptions used calculating net periodic benefit cost, Discount rate 3.50% 4.00% 4.25%
Defined benefit plan, assumptions used calculating net periodic benefit cost, Rate of compensation increase 2.50% 3.00% 3.25%
Director's Retirement Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate 4.00% 3.50%  
Defined benefit plan, assumptions used calculating net periodic benefit cost, Discount rate 4.00% 4.00% 4.25%
Defined benefit plan, assumptions used calculating benefit obligation, Change in consumer price index 2.00% 1.50%  
Defined benefit plan, assumptions used calculating net periodic benefit cost, Changes in consumer price index 2.00% 1.50% 2.25%
Defined Benefit Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined benefit plan, assumptions used calculating benefit obligation, Discount rate 4.25%    
Defined benefit plan, assumptions used calculating benefit obligation, Rate of compensation increase 3.00%    
Defined benefit plan, assumptions used calculating benefit obligation, Expected long-term return on plan assets 5.00%