Employee Benefits - Postretirement Health Care Plan Status (Detail) - Other Postretirement Plan - USD ($) $ in Millions |
Dec. 31, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
---|---|---|---|
Defined Benefit Plan Disclosure [Line Items] | |||
Net Postretirement Benefit Obligation | $ 28.1 | $ 34.4 | $ 34.1 |
Retirees and Dependents | |||
Defined Benefit Plan Disclosure [Line Items] | |||
Net Postretirement Benefit Obligation | 23.5 | 27.7 | |
Actives Eligible for Benefits | |||
Defined Benefit Plan Disclosure [Line Items] | |||
Net Postretirement Benefit Obligation | $ 4.6 | $ 6.7 |