Pension and Postretirement Benefit Plans - Weighted Average Assumptions Used to Determine Benefit Plan's Net Periodic Cost (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate (percent)	4.20%	3.85%	4.85%
Expected long-term rate of return on assets (percent)	7.00%	7.00%	7.00%
Rates of increase in compensation levels (percent)	3.50%	3.50%	3.50%
Postretirement
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discount rate (percent)	4.20%	3.85%	4.85%
Expected long-term rate of return on assets (percent)	0.00%	0.00%	0.00%
Rates of increase in compensation levels (percent)	0.00%	0.00%	0.00%