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Benefit Plans Actuarial Calculation Assumptions (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pension Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 4.04% 4.24% 3.88%
Net periodic benefit cost, expected return on plan assets 7.00% 7.00% 7.00%
Net periodic benefit cost, rate of compensation increase 4.00% 4.00% 4.00%
Benefit obligations, discount rate 3.52% 4.04%  
Benefit obligations, rate of compensation increase 4.00% 4.00%  
Other Postretirement Benefits Plan [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Net periodic benefit cost, discount rate 3.93% 4.10% 3.80%
Net periodic benefit cost, expected return on plan assets 7.00% 7.00% 7.00%
Benefit obligations, discount rate 3.45% 3.93%