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, 2019	Dec. 31, 2018
Schedule Of Reconciliation Of Changes In Fair Value Of Assets And Liabilities [Line Items]
Fair value at beginning of the year	$ 454.0
Fair value at end of the year	498.4	$ 454.0
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	259.6	273.6
Gain (loss) on assets held at end of year	30.2	(4.6)
Loss on assets sold during the year	(1.1)
Assets purchased	16.0	14.1
Assets sold	(14.9)	(14.5)
Transfer in		2.3
Currency exchange rate fluctuations	(6.3)	(11.3)
Fair value at end of the year	$ 283.5	$ 259.6

Amount of asset segregated and restricted to provide benefit under defined benefit plan. Asset includes, but is not limited to, stock, bond, other investment, earning from investment, and contribution by employer and employee.

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