Benefit Plans - Plan Assets Using Fair Value Methodologies (Detail) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 30.5	$ 28.4
Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.4
Total | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.2
Total | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.2	11.9
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.2
Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.2
Level 1 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Level 2 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Level 2 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.2
Level 3 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Level 3 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	14.2	11.9
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 16.1	$ 16.5