Retirement Plans - Weighted Average Assumptions Used to Determine Benefit Obligation (Detail)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Ultimate	0.00%	0.00%
Discount rate	4.50%	4.10%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Ultimate	4.90%	4.90%
Discount rate	4.20%	3.90%
Pre-Age 65 | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Current	0.00%	0.00%
Pre-Age 65 | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Current	6.10%	7.90%
Post-Age 65 | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Current	0.00%	0.00%
Post-Age 65 | Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Health care cost trend, Current	6.10%	7.90%