Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Change in benefit obligations
Service cost	$ 3.3	$ 2.6	$ 4.1
Interest cost	2.9	7.3	11.5
Change in plan assets
Fair value of plan assets beginning of year	31.0
Company contributions		11.1
Fair value of plan assets end of year	33.7	31.0
Pension plans
Change in benefit obligations
Benefit obligation beginning of year	112.1	277.9
Service cost	3.3	2.6
Interest cost	2.9	7.3
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	0.0	(1.5)
Actuarial loss	9.3	8.0
Translation (gain) loss	1.4	0.1
Benefits paid	8.2	182.3
Benefit obligation end of year	120.8	112.1	277.9
Change in plan assets
Fair value of plan assets beginning of year	31.0	180.7
Actual return on plan assets	3.0	16.0
Company contributions	7.1	18.0
Defined Benefit Plan, Plan Assets, Payment for Settlement	0.0	(1.5)
Translation gain (loss)	0.8	0.1
Benefits paid	8.2	182.3
Fair value of plan assets end of year	33.7	31.0	180.7
Funded status
Plan assets less than benefit obligation	(87.1)	(81.1)
Other post-retirement plans
Change in benefit obligations
Benefit obligation beginning of year	14.6	14.9
Service cost	0.0	0.0
Interest cost	0.4	0.6
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	0.0	0.0
Actuarial loss	0.1	2.0
Translation (gain) loss	0.0	0.0
Benefits paid	1.3	2.9
Benefit obligation end of year	13.8	14.6	14.9
Change in plan assets
Fair value of plan assets beginning of year	0.0	0.0
Actual return on plan assets	0.0	0.0
Company contributions	1.3	2.9
Defined Benefit Plan, Plan Assets, Payment for Settlement	0.0	0.0
Translation gain (loss)	0.0	0.0
Benefits paid	1.3	2.9
Fair value of plan assets end of year	0.0	0.0	$ 0.0
Funded status
Plan assets less than benefit obligation	$ (13.8)	$ (14.6)