Weighted Average Assumptions used in Determining Net Periodic Benefit Cost (Detail)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Pension
Defined Benefit Plan Disclosure [Line Items]
Discount rate	4.27%	4.28%	5.50%
Rate of return	8.31%	8.27%	8.31%
Initial healthcare trend rate
Ultimate healthcare trend rate
Other Benefits
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.83%	3.95%	5.10%
Rate of return
Initial healthcare trend rate	8.15%	8.50%	8.00%
Ultimate healthcare trend rate	5.00%	5.00%	5.00%