Employee Benefits Employee Benefits, Assumptions used to determine benefit obligations (Details)	Dec. 31, 2016	Dec. 31, 2015
Canadian pension plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.80%	4.10%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Rate of Compensation Increase	3.00%	3.00%
Salaried VEBA
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.60%	3.90%