Employee Benefits, Total charges (income) related to all benefit plans (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of Net Periodic Benefit Cost (Income)
Defined contribution plans	$ 8.8	$ 8.8	$ 8.9
Deferred compensation plan	1.6	1.0	1.8
Multiemployer pension plans	5.0	4.7	4.6
Net periodic postretirement benefit cost	7.0	6.6	4.8
VEBAs
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	6.6	6.1	4.5
Canadian pension plan | Canadian pension plan
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	0.4	0.4	0.3
Other expenses
Components of Net Periodic Benefit Cost (Income)
Net periodic postretirement benefit cost	$ 22.4	$ 21.0	$ 20.1