Employee Benefits - Amounts Recognized in Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension settlement charge	$ 98.7	$ 65.9	$ 1.6
Net loss (gain)	(142.4)	(41.8)	(14.0)
Pension Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	(28.7)	29.9
Amortization of net actuarial loss (gain)	(14.0)	(16.4)
Amortization of prior service cost (credit)		(0.1)
Pension settlement charge	(98.7)	(65.9)	$ (1.6)
Net loss (gain)	(141.4)	(52.5)
Other Postretirement Benefits [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net actuarial loss (gain)	(7.0)	0.8
Amortization of net actuarial loss (gain)	6.0	6.9
Amortization of prior service cost (credit)	0.5	2.2
Net loss (gain)	$ (0.5)	$ 9.9