Employee Benefits, Assumptions used to determine benefit obligations (Details)	Dec. 31, 2019	Dec. 31, 2018
Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	2.95%	3.90%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Expected Long-term Rate of Return on Plan Assets	5.50%	5.50%
Canadian pension plan | Canadian pension plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.10%	3.90%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate	4.45%	4.45%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.00%	3.00%