Postretirement Benefits Other Than Pensions - Weighted Average Assumptions Used to Determine Net Postretirement Benefit Expense (Detail) - Other Postretirement Benefit Plan [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]
Discount rate	3.32%	3.94%	3.08%
Measurement date	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013