Pensions and Postretirement Benefits (Summary of Assumptions Used in the valuation of pension and postretirement benefit obligations) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits
Assumptions used to determine benefit obligation at year-end
Discount rate	3.52%	3.91%	4.13%
Rate of compensation increase	3.00%	3.00%	3.00%
Assumptions used to determine expense
Discount rate for benefit obligations	3.90%	4.13%	3.82%
Discount rate for service costs	3.98%	4.20%	3.82%
Discount rate for interest costs	3.20%	3.27%	3.82%
Expected return on plan assets	8.25%	8.25%	8.25%
Rate of compensation increase	3.00%	3.00%	3.00%
Postretirement Benefits
Assumptions used to determine benefit obligation at year-end
Discount rate	3.32%	3.63%	3.80%
Medical drug benefits rate increase	6.50%	6.50%	6.75%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%
Assumptions used to determine expense
Discount rate for benefit obligations	3.61%	3.76%	3.60%
Discount rate for service costs	4.24%	4.44%	3.60%
Discount rate for interest costs	2.90%	2.89%	3.60%
Medical health care benefits rate increase	6.50%	6.50%	6.75%
Ultimate health care cost trend rate	5.00%	5.00%	5.00%