Defined Benefit Plans - Reconciliation of Level Three Measurements (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	$ 784.9
Ending balance	816.0	$ 784.9
Group annuity/insurance contracts (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Beginning balance	24.8	24.2
Actual return on assets related to assets still held	0.7	0.6
Ending balance	$ 25.5	$ 24.8