Employee Benefit Plans - Accumulated and Projected Benefit Obligations (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations:	$ 84.4	$ 86.6
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations:	665.3	562.3
Projected benefit obligations:	665.5	562.7	$ 584.8
Pension Plans [Member] | Qualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations:	625.3	518.7
Projected benefit obligations:	625.3	518.7
Pension Plans [Member] | Nonqualified Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligations:	40.0	43.6
Projected benefit obligations:	$ 40.2	$ 44.0