XML 112 R96.htm IDEA: XBRL DOCUMENT v3.6.0.2
Pension and other postretirement benefits - weighted average assumptions used in determining benefit obligations (Detail)
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Dec. 31, 2014
Pension      
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discount rate 4.20% 4.50%  
Rate of compensation increase 2.80% 2.80%  
Other Benefits      
Defined Benefit Plans And Other Postretirement Benefit Plans Table Text Block [Line Items]      
Discount rate 4.10% 4.30%  
Initial healthcare trend rate 7.90% 8.40%  
Ultimate healthcare trend rate 5.00% 5.00% 5.00%