Retirement Plans - Reconciliation of Benefit Obligation, Plan Assets and Funded Status of Plans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	$ 933.0	$ 1,044.8
Service cost	1.0	0.7	$ 0.7
Interest cost	33.3	31.3	31.6
Plan participants' contributions	0.0	0.0
Medicare reimbursements	0.0	0.0
Actuarial loss (gain)	126.7	(64.3)
Plan amendments and other	2.1	0.7
Settlements	(0.4)	(8.5)
Foreign currency translation	14.2	(26.5)
Benefits paid	(49.2)	(45.2)
Benefit obligation at end of year	1,060.7	933.0	1,044.8
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	878.8	979.3
Actual return (loss) on assets	133.4	(31.7)
Settlements	(0.4)	(8.7)
Employer contributions	9.0	10.7
Company reimbursements	0.0	0.0
Medicare reimbursements	0.0	0.0
Plan participants' contributions	0.0	0.0
Foreign currency translation	14.0	(25.6)
Benefits paid	(49.2)	(45.2)
Fair value of plan assets at end of year	985.6	878.8	979.3
Total net pension and OPEB liability recognized as of December 31	(75.1)	(54.2)
OPEB
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of year	277.1	342.4
Service cost	0.0	(3.7)	1.3
Interest cost	10.1	9.4	11.1
Plan participants' contributions	7.5	10.1
Medicare reimbursements	6.6	6.4
Actuarial loss (gain)	16.9	(19.7)
Plan amendments and other	0.0	(32.6)
Settlements	0.0	0.0
Foreign currency translation	0.1	(1.3)
Benefits paid	(28.5)	(33.9)
Benefit obligation at end of year	289.8	277.1	342.4
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of year	208.9	228.6
Actual return (loss) on assets	33.6	(9.5)
Settlements	0.0	0.0
Employer contributions	7.2	7.2
Company reimbursements	(7.6)	0.0
Medicare reimbursements	6.6	6.4
Plan participants' contributions	7.5	10.1
Foreign currency translation	0.0	0.0
Benefits paid	(28.5)	(33.9)
Fair value of plan assets at end of year	227.7	208.9	$ 228.6
Total net pension and OPEB liability recognized as of December 31	$ (62.1)	$ (68.2)