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Pension and Other Benefit Plans - Defined Benefit Plan Weighted Average Assumptions Used in Calculating Benefit Obligation and Net Periodic Benefit Cost For US Postretirement Medical Plan (Detail)
12 Months Ended
Dec. 31, 2015
Dec. 31, 2014
Dec. 31, 2013
Pension Plans Postretirement And Other Employee Benefits [Line Items]      
Discount rate 4.50% 4.15%  
Current medical cost trend rate 7.00% 7.00%  
Ultimate medical cost trend rate 5.00% 5.00%  
Year that the rate reaches the ultimate trend rate 2023 2023  
Postretirement medical plan      
Pension Plans Postretirement And Other Employee Benefits [Line Items]      
Discount rate 4.15% 4.85% 4.25%
Return on plan assets 7.00% 7.00% 7.00%
Current medical cost trend rate 7.00% 7.25% 7.50%
Ultimate medical cost trend rate 5.00% 5.00% 5.00%
Year that the rate reaches the ultimate trend rate 2023 2023 2023