Pension and Other Postretirement Benefits - Schedule of Assumed Health Care Cost Trend Rates (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Health care cost trend rate assumed for next year	5.50%	5.50%	5.50%
Rate to which the cost trend rate gradually declines	4.50%	4.50%	4.50%
Year that the rate reaches the rate at which it is assumed to remain	2020	2019	2018