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, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligations, Expected return on plan assets	5.51%
Weighted average expected return on plan asset	5.51%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligations, Discount rate	3.85%	4.07%
Benefit Obligations, Expected return on plan assets	5.05%	5.37%
Benefit Obligation, Rate of compensation increase	3.28%	3.28%
Net Periodic Benefit Expense, Discount rate	3.35%	3.54%
Weighted average expected return on plan asset	5.05%	5.37%
Net Periodic Benefit Expense, Rate of compensation increase	3.52%	3.52%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Benefit Obligations, Discount rate	3.42%	3.73%
Benefit Obligations, Expected return on plan assets	0.00%	0.00%
Benefit Obligation, Rate of compensation increase	0.00%	0.00%
Net Periodic Benefit Expense, Discount rate	4.42%	4.32%
Weighted average expected return on plan asset	0.00%	0.00%
Net Periodic Benefit Expense, Rate of compensation increase	0.00%	0.00%