Pension and Other Postretirement Benefits - Multiemployer Plans (Details 6) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014 employees	Dec. 31, 2013	Dec. 31, 2012
Multiemployer Plans [Line Items]
Contributions to multiemployer plans	$ 24.6	$ 22.1	$ 19.6
Number of Employees	8,000
Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Contributions to multiemployer plans	8.1	7.3	7.0
IAM National Pension Fund's National Pension Plan [Member]
Multiemployer Plans [Line Items]
Contributions to multiemployer plans	$ 16.5	$ 14.8	$ 12.6
Mansfield Works [Member] | Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Number of Employees	300
Walbridge Tube [Member] | Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Number of Employees	100
Ashland Works [Member] | Steelworkers Pension Trust [Member]
Multiemployer Plans [Line Items]
Number of Employees	830
Butler Works [Member] | IAM National Pension Fund's National Pension Plan [Member]
Multiemployer Plans [Line Items]
Number of Employees	1,200
Middletown Works [Member] | IAM National Pension Fund's National Pension Plan [Member]
Multiemployer Plans [Line Items]
Number of Employees	1,640
Workforce Subject to Collective Bargaining Arrangements Expiring within One Year [Member] | Zanesville Works [Member] | IAM National Pension Fund's National Pension Plan [Member]
Multiemployer Plans [Line Items]
Number of Employees	130