Employee Benefits - Net Periodic Benefit Costs Actuarial Assumptions (Details)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Ultimate health care cost trend rate	4.50%
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Rate of compensation increase	3.25%	3.25%	3.25%
Expected long-term rate of return on plan assets	6.50%	6.50%	7.00%
Pension Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.14%	3.25%	3.34%
Pension Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.69%	4.14%	4.46%
Other Postretirement Benefits Plan
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.26%	3.90%	4.15%
Expected long-term rate of return on plan assets	4.00%	5.00%	7.00%
Ultimate health care cost trend rate	4.50%	4.50%	4.50%
Other Postretirement Benefits Plan | Minimum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	5.00%	5.00%	5.00%
Other Postretirement Benefits Plan | Maximum
Defined Benefit Plan Disclosure [Line Items]
Initial health care cost trend rate	7.00%	7.00%	5.25%