Retirement Plans - Reconciliation of Benefit Obligation, Plan Assets and Funded Status of Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 1,060.7	$ 933.0
Service cost	1.0	1.0	$ 0.7
Interest cost	27.4	33.3	31.3
Plan participants' contributions	0.0	0.0
Medicare reimbursements	0.0	0.0
Actuarial loss	86.0	126.7
Plan amendments and other	0.1	2.1
Settlements	(6.6)	(0.4)
Foreign currency translation	15.0	14.2
Benefits paid	(45.6)	(49.2)
Benefit obligation at end of year	1,138.0	1,060.7	933.0
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	985.6	878.8
Actual return on assets	132.1	133.4
Settlements	(6.6)	(0.4)
Employer contributions	9.2	9.0
Company reimbursements	0.0	0.0
Medicare reimbursements	0.0	0.0
Plan participants' contributions	0.0	0.0
Foreign currency translation	15.5	14.0
Benefits paid	(45.6)	(49.2)
Fair value of plan assets at end of year	1,090.2	985.6	878.8
Total net pension and OPEB liability recognized as of December 31	(47.8)	(75.1)
OPEB
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	289.8	277.1
Service cost	0.0	0.0	(3.7)
Interest cost	7.3	10.1	9.4
Plan participants' contributions	7.8	7.5
Medicare reimbursements	7.9	6.6
Actuarial loss	8.1	16.9
Plan amendments and other	0.0	0.0
Settlements	0.0	0.0
Foreign currency translation	0.0	0.1
Benefits paid	(27.5)	(28.5)
Benefit obligation at end of year	293.4	289.8	277.1
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	227.7	208.9
Actual return on assets	21.0	33.6
Settlements	0.0	0.0
Employer contributions	7.2	7.2
Company reimbursements	(6.9)	(7.6)
Medicare reimbursements	7.9	6.6
Plan participants' contributions	7.8	7.5
Foreign currency translation	0.0	0.0
Benefits paid	(27.5)	(28.5)
Fair value of plan assets at end of year	237.2	227.7	$ 208.9
Total net pension and OPEB liability recognized as of December 31	$ (56.2)	$ (62.1)