Postretirement Health Care Plans - Net Periodic Postretirement Health Care Cost (Detail) - Postretirement Health Coverage - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 26, 2020	Sep. 28, 2019	Sep. 26, 2020	Sep. 28, 2019
Postretirement Health Care Plans [Line Items]
Interest cost	$ 0.4	$ 0.4	$ 1.1	$ 1.4
Expected return on plan assets	(0.2)	(0.1)	(0.5)	(0.5)
Amortization of unrecognized gain	0.0	(0.2)	0.0	(0.6)
Net periodic cost	$ 0.2	$ 0.1	$ 0.6	$ 0.3