Employee and Retiree Benefit Plans (Weighted-Average Assumptions used in Measurement of Benefit Obligations and Net Periodic Benefit Expense) (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligations, Expected return on plan assets	5.64%
Net Periodic Benefit Expense, Expected return on plan assets	5.64%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligations, Discount rate	3.42%	3.94%
Benefit Obligations, Expected return on plan assets	5.64%	5.62%
Benefit Obligation, Rate of compensation increase	3.52%	3.52%
Net Periodic Benefit Expense, Discount rate	3.66%	3.84%
Net Periodic Benefit Expense, Expected return on plan assets	5.64%	5.62%
Net Periodic Benefit Expense, Rate of compensation increase	3.52%	3.52%
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligations, Discount rate	3.73%	4.41%
Net Periodic Benefit Expense, Discount rate	4.33%	4.24%