Defined Benefit Plans - Obligations and Funded Status (Detail) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Change in the Projected Benefit Obligation (PBO):
Recognition of actuarial losses (gains)		$ 3.8	$ (0.5)	$ 1.9
Change in Plan Assets:
Beginning balance		656.6
Ending balance		599.6	656.6
Pension Benefits [Member]
Change in the Projected Benefit Obligation (PBO):
Projected benefit obligation at beginning of year		832.4	791.7
Service cost		0.5	0.6
Interest cost		30.7	33.3
Recognition of actuarial losses (gains)		(63.1)	40.6
Benefits paid		(37.3)	(33.8)
Projected benefit obligation at end of year		763.2	832.4	791.7
Accumulated benefit obligation at end of year (excludes the impact of future compensation increases)		763.2	832.4
Change in Plan Assets:
Beginning balance		656.6	577.7
Actual return on plan assets		(30.7)	83.2
Employer contributions		11.0	29.5
Benefits paid		(37.3)	(33.8)
Ending balance		599.6	656.6	577.7
Funded status (Fair value of plan assets less PBO)		(163.6)	(175.8)
Postretirement Benefits [Member]
Change in the Projected Benefit Obligation (PBO):
Projected benefit obligation at beginning of year		1.6	3.6
Recognition of actuarial losses (gains)	$ 0.9	(0.2)	(1.4)
Benefits paid			(0.4)
Foreign exchange			(0.2)
Projected benefit obligation at end of year		1.4	1.6	$ 3.6
Change in Plan Assets:
Employer contributions			0.5
Benefits paid			(0.5)
Funded status (Fair value of plan assets less PBO)		$ (1.4)	$ (1.6)