Employee Benefits - Schedule of Significant Assumptions of Pension and Other Postretirement Benefit Plans (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Plan Asset
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.75%	4.28%	4.66%
Rate of compensation increase	3.02%	3.07%	3.10%
Discount rate	4.28%	4.66%	4.24%
Expected return on plan assets	6.49%	7.02%	6.91%
Rate of compensation increase	3.07%	3.10%	3.12%
Other Postretirement Benefit Cost
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.73%	4.26%	4.67%
Discount rate	4.26%	3.66%	4.24%
Expected return on plan assets	5.09%	5.37%	4.92%
Other Postretirement Benefit Cost | Maximum
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate, benefit obligations, percentage	7.00%	7.00%	6.50%
Health care cost trend rate, net periodic costs, percentage	7.00%	6.50%	6.75%
Other Postretirement Benefit Cost | Minimum
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend rate, benefit obligations, percentage	4.50%	5.00%	5.00%
Health care cost trend rate, benefit obligation, year	2026	2021	2021
Health care cost trend rate, net periodic costs, percentage	5.00%	5.00%	5.00%
Health care cost trend rate, net periodic costs, year	2021	2021	2021