Pension Plans, Postretirement and Other Employee Benefits - Assumptions Used to Determine Postretirement Cost (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Discount rate, Benefit Obligation	4.20%	4.30%
Discount rate, Net Periodic Benefit Cost	4.30%	4.10%	4.80%