Employee Benefits, Benefit obligations and funded status of our Canadian pension and the VEBAs (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Change in plan assets:
Fair value of plan assets at beginning of year	$ 72.3
Fair value of plan assets at end of year	68.1	$ 72.3
Accrued Annual Veba Contribution	2.1	15.7
Net liabilities of Salaried VEBA	32.4	31.9
VEBAs
Change in benefit obligation:
Obligation at beginning of year	90.0	86.8
Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss)	0.0	0.0
Defined Benefit Plan, Service Cost	0.0	0.0
Defined Benefit Plan, Interest Cost	2.8	3.0
Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment	6.9	7.3
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	6.8	0.5
Benefits paid by VEBA	(7.3)	(6.6)
Obligation at end of year	85.6	90.0
Change in plan assets:
Fair value of plan assets at beginning of year	58.1	58.2
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	0.3	3.6
Defined Benefit Plan, Plan Assets, Contributions by Employer	2.1	2.9
Benefits paid by VEBA	(7.3)	(6.6)
Fair value of plan assets at end of year	53.2	58.1
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(32.4)	(31.9)
Salaried VEBA
Change in plan assets:
Actuarial (gain) loss due to projected lower benefit utilization	(2.2)	(1.0)
Actuarial (Gain) Loss Due To Change In Discount Rate	(5.1)	3.0
Actuarial (Gain) Loss Due To Changes In Census Data	0.5	(2.5)
Accrued Annual Veba Contribution	2.1	2.9
Defined Benefit Plan, Funded (Unfunded) Status of Plan	(32.4)	(31.9)
Union VEBA
Change in plan assets:
Accrued Annual Veba Contribution		12.8
Canadian pension plan
Change in plan assets:
Defined Benefit Plan, Benefit Obligation, Contributions by Plan Participant	0.1	0.1
Canadian pension plan | Canadian pension plan
Change in benefit obligation:
Obligation at beginning of year	8.5	7.0
Defined Benefit Plan, Benefit Obligation, Foreign Currency Translation Gain (Loss)	(0.7)	0.5
Defined Benefit Plan, Service Cost at Balance Sheet Exchange Rate	0.3	0.3
Defined Benefit Plan, Interest Cost at Balance Sheet Exchange Rate	0.3	0.3
Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss)	0.6	(0.6)
Obligation at end of year	7.3	8.5
Change in plan assets:
Fair value of plan assets at beginning of year	7.3	6.1
Defined Benefit Plan, Plan Assets, Foreign Currency Translation Gain (Loss)	(0.6)	0.5
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss)	(0.2)	0.5
Defined Benefit Plan, Plan Assets, Contributions by Employer	0.5	0.4
Defined Benefit Plan, Plan Assets, Benefits Paid	0.6	0.3
Fair value of plan assets at end of year	6.5	7.3
Defined Benefit Plan, Funded (Unfunded) Status of Plan	$ (0.8)	$ (1.2)