Employee Benefits - Weighted-Average Rates to Determine Net Postretirement Benefit Cost (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.25%	3.75%	3.75%
Expected return on plan assets	4.75%	6.00%	6.00%
Other Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.50%	3.75%	4.00%
Expected return on plan assets	4.50%	4.50%	4.50%