Postretirement Benefits Other Than Pensions - Assumptions Used to Determine Benefit Obligation (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	3.57%	3.32%	3.94%
Measurement date	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013