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Pensions and Other Postretirement Benefits (Weighted-average Assumptions Used) (Details)
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Pensions [Member]      
Weighted-average assumptions used to determine projected benefit obligation [Abstract]      
Discount rate 3.51% 3.81% 3.99%
Rate of compensation increase 2.75% 2.75% 2.75%
Weighted-average assumptions used to determine net periodic benefit cost [Abstract]      
Rate to determine current service cost 4.11% 4.24% 3.87%
Rate to determine interest cost 3.15% 3.27% 3.87%
Rate of compensation increase 2.75% 2.75% 3.00%
Expected return on plan assets 7.00% 7.00% 7.00%
Expected return on plan asset assumption to be used in future year (in hundredths) 7.00%    
Period in years over which realized and unrealized gains/losses and appreciation/depreciation in the value of the investments are recognized based on the companies election to use market related value 5 years    
Other postretirement benefits [Member]      
Weighted-average assumptions used to determine projected benefit obligation [Abstract]      
Discount rate 3.59% 3.96% 4.14%
Rate of compensation increase 2.75% 2.75% 2.75%
Weighted-average assumptions used to determine net periodic benefit cost [Abstract]      
Rate to determine current service cost 4.43% 4.59% 3.86%
Rate to determine interest cost 3.29% 3.35% 3.86%
Rate of compensation increase 2.75% 2.75% 3.00%