Postretirement Benefit Plans - Summary of Weighted Average Assumptions Used to Calculate Projected Benefit Obligations (Detail) |
Dec. 31, 2016 |
Dec. 31, 2015 |
|---|---|---|
| Pension and Other Postretirement Benefit Expense [Abstract] | ||
| Discount rate | 2.00% | 2.50% |
| Rate of compensation increase | 1.90% | 2.20% |