Employee Benefit Plans - Benefit Payments (Detail) $ in Millions |
Dec. 31, 2016
USD ($)
|
|---|---|
| Defined Benefit Pension Plans | |
| Defined Benefit Plan Disclosure [Line Items] | |
| 2017 | $ 20.1 |
| 2018 | 20.4 |
| 2019 | 20.9 |
| 2020 | 22.1 |
| 2021 | 22.6 |
| Next 5 years | 124.4 |
| OPEB | |
| Defined Benefit Plan Disclosure [Line Items] | |
| 2017 | 0.4 |
| 2018 | 0.4 |
| 2019 | 0.4 |
| 2020 | 0.4 |
| 2021 | 0.4 |
| Next 5 years | $ 2.2 |