Retirement Plans - Reconciliation of Beginning and Ending Balances for Level 3 Assets of Plan Measured at Fair Value (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	$ 212.5	$ 282.3
Fair value of plan assets at end of year	228.9	212.5
Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets at beginning of year	99.6	124.2
Settlements	(1.4)	(1.5)
Unrealized gain	10.4	(23.1)
Fair value of plan assets at end of year	$ 108.6	$ 99.6