Benefit Plans - Plan Assets Using Fair Value Methodologies (Detail) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 34.4	$ 33.7
Total
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.3	10.1
Total | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3	0.1
Total | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.0	10.0
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3	0.1
Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3	0.1
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	0.0
Level 2 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	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	11.0	10.0
Level 3 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Level 3 | Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.0	10.0
Investments measured at NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 23.1	$ 23.6