Annual report pursuant to Section 13 and 15(d)

Pension and Other Postretirement Benefit Programs - Asset Allocation (Details)

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Pension and Other Postretirement Benefit Programs - Asset Allocation (Details) - Pension Plan
Dec. 31, 2017
Dec. 31, 2016
U.S. Pension Plan | Fixed income securities    
Defined Benefit Plan Disclosure [Line Items]    
Target Weight End of Period 60.00%  
Position at End of Period 56.00% 60.00%
U.S. Pension Plan | Equities    
Defined Benefit Plan Disclosure [Line Items]    
Target Weight End of Period 40.00%  
Position at End of Period 44.00% 40.00%
Canadian Pension Plan | Fixed income securities    
Defined Benefit Plan Disclosure [Line Items]    
Target Weight End of Period 50.00%  
Position at End of Period 49.00% 49.00%
Canadian Pension Plan | Equities    
Defined Benefit Plan Disclosure [Line Items]    
Target Weight End of Period 48.00%  
Position at End of Period 49.00% 48.00%
Canadian Pension Plan | Other    
Defined Benefit Plan Disclosure [Line Items]    
Target Weight End of Period 2.00%  
Position at End of Period 2.00% 3.00%