Labor Union Contracts (Details)	3 Months Ended
	Mar. 31, 2017
Employees subject to collective bargaining arrangements, expiring within subsequent calendar year
Concentration risk
Number of unionized employees	12,000
Workforce subject to collective bargaining arrangements, expiring October 7, 2017
Concentration risk
Number of unionized employees	10,000
Total number of employees | Unionized employees concentration risk
Concentration risk
Concentration risk (percent)	37.00%
Total number of employees | Unionized employees concentration risk | Employees subject to collective bargaining arrangements, expiring within subsequent calendar year
Concentration risk
Concentration risk (percent)	30.00%
Total number of employees | Unionized employees concentration risk | Workforce subject to collective bargaining arrangements, expiring October 7, 2017
Concentration risk
Concentration risk (percent)	25.00%