Benefit Plans - Summary of Weighted Average Assumptions (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Expected return in plan assets	2.50%	2.50%	0.75%
Minimum
Defined Benefit Plan Disclosure [Line Items]
Discount rate for obligations	3.00%	2.50%	0.75%
Discount rate for net periodic benefit costs	2.50%	0.75%	1.00%
Rate of compensation increases	2.50%	2.50%	2.00%
Maximum
Defined Benefit Plan Disclosure [Line Items]
Discount rate for obligations	11.60%	11.60%	10.10%
Discount rate for net periodic benefit costs	11.60%	10.10%	9.75%
Rate of compensation increases	14.00%	13.00%	13.00%