Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Change in benefit obligations
Service cost	$ 2.6	$ 4.1	$ 11.7
Interest cost	7.3	11.5	16.4
Change in plan assets
Fair value of plan assets beginning of year	180.7
Company contributions	11.1
Fair value of plan assets end of year	31.0	180.7
Pension plans
Change in benefit obligations
Benefit obligation beginning of year	277.9	473.8
Service cost	2.6	4.1
Interest cost	7.3	11.5
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	(1.5)	0.0
Actuarial loss	8.0	(23.6)
Translation (gain) loss	0.1	(0.2)
Benefits paid	182.3	187.7
Benefit obligation end of year	112.1	277.9	473.8
Change in plan assets
Fair value of plan assets beginning of year	180.7	382.8
Actual return on plan assets	16.0	(21.4)
Company contributions	18.0	7.1
Translation gain (loss)	0.1	(0.1)
Benefits paid	182.3	187.7
Fair value of plan assets end of year	31.0	180.7	382.8
Funded status
Plan assets less than benefit obligation	(81.1)	(97.2)
Other post-retirement plans
Change in benefit obligations
Benefit obligation beginning of year	14.9	17.5
Service cost	0.0	0.0
Interest cost	0.6	0.6
Defined Benefit Plan, Benefit Obligation, Payment for Settlement	0.0	0.0
Actuarial loss	2.0	(1.4)
Translation (gain) loss	0.0	0.0
Benefits paid	2.9	1.8
Benefit obligation end of year	14.6	14.9	17.5
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	2.9	1.8
Translation gain (loss)	0.0	0.0
Benefits paid	2.9	1.8
Fair value of plan assets end of year	0.0	0.0	$ 0.0
Funded status
Plan assets less than benefit obligation	$ (14.6)	$ (14.9)