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Employee Benefits - Weighted Average Assumptions Used to Determine Postretirement Benefit Expense and Obligation (Detail)
12 Months Ended
Dec. 31, 2013
Dec. 31, 2012
Expense [Member]
   
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 4.00% 4.60%
Current medical cost trend rate 6.75% 7.00%
Ultimate medical cost trend rate 4.75% 4.75%
Medical cost trend rate decreases to ultimate rate in year 2021 2021
Liability [Member]
   
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 4.80% 4.00%
Current medical cost trend rate 6.50% 6.75%
Ultimate medical cost trend rate 4.75% 4.75%
Medical cost trend rate decreases to ultimate rate in year 2021 2021