Employee Benefits, Benefit obligations and funded status of our Canadian pension and the VEBAs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Fair value of plan assets at beginning of year	$ 68.1
Fair value of plan assets at end of year	70.6	$ 68.1
Accrued Annual VEBA Contribution	2.9	2.1
Net liabilities of Salaried VEBA	32.6	32.4
VEBAs
Change in benefit obligation:
Obligation at beginning of year	85.6	90.0
Foreign currency translation adjustment	0.0	0.0
Defined Benefit Plan, Service Cost	0.1	0.1	$ 0.0
Defined Benefit Plan, Interest Cost	3.2	2.7	3.0
Prior service cost	2.5	6.9
Actuarial loss (gain)	6.4	(6.8)
Benefits paid by Salaried VEBA	(7.6)	(7.3)
Obligation at end of year	90.2	85.6	90.0
Change in plan assets:
Fair value of plan assets at beginning of year	53.2	58.1
Actual return on assets	9.1	0.3
Company contributions	2.9	2.1
Benefits paid by Salaried VEBA	(7.6)	(7.3)
Fair value of plan assets at end of year	57.6	53.2	58.1
Net Funded Status	(32.6)	(32.4)
Salaried VEBA
Change in plan assets:
Actuarial (gain) loss due to projected lower benefit utilization	(0.5)	(2.2)
Actuarial (gain) loss due to change in discount rate	6.8	(5.1)
Actuarial (gain) loss due to changes in census data	0.1	0.5
Accrued Annual VEBA Contribution	2.9	2.1
Union VEBA
Change in plan assets:
Accrued Annual VEBA Contribution		12.8
Canadian pension plan | Canadian pension plan
Change in benefit obligation:
Obligation at beginning of year	7.3	8.5
Foreign currency translation adjustment	0.3	(0.7)
Defined Benefit Plan, Service Cost	0.3	0.3	0.3
Defined Benefit Plan, Interest Cost	0.3	0.3	0.3
Actuarial loss (gain)	1.1	(0.6)
Plan participant contributions	0.0	(0.1)
Benefits paid by Company	(0.5)	(0.6)
Obligation at end of year	8.8	7.3	8.5
Change in plan assets:
Fair value of plan assets at beginning of year	6.5	7.3
Foreign currency translation adjustment	0.3	(0.6)
Actual return on assets	1.0	(0.2)
Plan participant contributions	0.0	0.1
Company contributions	0.5	0.5
Benefits paid by Company	(0.5)	(0.6)
Fair value of plan assets at end of year	7.8	6.5	$ 7.3
Net Funded Status	$ (1.0)	$ (0.8)