Employee Benefit Plans - Rollforward of Change in Fair Value of Level 3 Assets (Detail) - Level 3 - Defined Benefit Pension Plans - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items] | ||
| Fair value at beginning of year | $ 236.2 | $ 254.1 |
| Gain on assets held at end of year | 4.1 | 6.5 |
| Gain on assets sold during the year | 0.3 | |
| Assets purchased | 13.1 | 13.7 |
| Assets sold | (13.4) | (12.4) |
| Currency exchange rate fluctuations | (9.5) | (26.0) |
| Fair value at end of year | $ 230.5 | $ 236.2 |