Employee Benefits, Total charges (income) related to all benefit plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Components of Net Periodic Benefit Cost (Income)
Defined Contribution Plan, Cost	$ 8.8	$ 8.9	$ 8.9
Deferred Compensation Arrangement with Individual, Compensation Expense	1.0	1.8	0.9
Contributions of the Company	4.7	4.6	4.7
Net periodic postretirement benefit cost	6.6	4.8	3.7
VEBAs
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	6.1	4.5	3.4
All Other | VEBAs
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	6.1	4.5	3.4
Canadian pension plan | Canadian pension plan
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	0.4	0.3	0.3
Canadian pension plan | Fabricated Products | Canadian pension plan
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	0.4	0.3	0.3
Other expenses
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	$ 21.0	$ 20.1	$ 18.1