Employee Benefits, Defined Benefit Plans Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued Annual VEBA Contribution	$ 2.9	$ 2.1
Defined Benefit Plan, Plan Assets, Amount	70.6	68.1
Union VEBA
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued Annual VEBA Contribution		12.8
Salaried VEBA
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Accrued Annual VEBA Contribution	2.9	2.1
VEBAs
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	90.2	85.6	$ 90.0
Defined Benefit Plan, Plan Assets, Amount	57.6	53.2	58.1
Salaried and certain hourly employee | Canadian pension plan | Maximum
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Estimated annual contribution to pension and other postretirement benefit plans	2.9
Canadian pension plan | Canadian pension plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Benefit Obligation	8.8	7.3	8.5
Defined Benefit Plan, Plan Assets, Amount	7.8	6.5	$ 7.3
Defined Benefit Plan, Accumulated Benefit Obligation	7.6	$ 6.4
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	$ 0.5
Canadian pension plan | Canadian pension plan | Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	36.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	35.00%
Canadian pension plan | Canadian pension plan | Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	62.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	60.00%
Canadian pension plan | Canadian pension plan | Short-term Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Actual Allocation, Percentage	2.00%
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage	5.00%