Defined Contribution and Defined Benefit Retirement - Schedule of Rollforward of Change in Fair Value of Level 3 Assets (Detail) - Defined Benefit Pension Plans - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Schedule Of Reconciliation Of Changes In Fair Value Of Assets And Liabilities [Line Items]
Fair value at beginning of the year	$ 491.7
Fair value at end of year	454.0	$ 491.7
Significant Unobservable Inputs (Level 3)
Schedule Of Reconciliation Of Changes In Fair Value Of Assets And Liabilities [Line Items]
Fair value at beginning of the year	273.6	230.5
Gain on assets held at end of year	(4.6)	11.0
Gain on assets sold during the year		0.2
Assets purchased	14.1	13.4
Assets sold	(14.5)	(13.8)
Transfer in	2.3
Currency exchange rate fluctuations	(11.3)	32.3
Fair value at end of year	$ 259.6	$ 273.6