Employee Benefit Plans - Benefit Obligations and Funded Status for Medical Plan (Details) - Postretirement Medical Plan $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Projected benefit obligation, beginning balance	$ 0.0
From Con-way acquisition	51.0
Service cost – benefits earned during the year	0.1
Interest cost on projected benefit obligation	0.3
Actuarial loss (gain)	3.3
Participant contributions	0.3
Benefits paid	(1.0)
Projected benefit obligation, ending balance	54.0
Funded status of the plan	(54.0)
Amounts recognized in the balance sheet consist of :
Current liabilities	(4.0)
Long-term liabilities	(50.0)
Total liability at December 31, 2015	$ (54.0)
Discount rate assumption as of December 31, 2015	4.20%