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Pension and Post-Employment Benefits - Defined Benefit Pension Plan (Detail) - United Kingdom Plan [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Plan assumptions at December 31, (%):
Discount rate	1.36%	1.95%	2.78%
Inflation rate	2.35%	2.25%	2.25%
Rate of return on plan assets - overall on bid-value	2.00%	2.50%	3.05%
Plan asset allocation by category (%):
Total plan asset allocation by category	100.00%	100.00%	100.00%
Cash [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	4.00%	4.00%	5.00%
Defined Benefit Plan Debt Securities And Insurance Contracts [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	86.00%	86.00%	83.00%
Defined Benefit Plan Equity Securities And Real Estate [Member]
Plan asset allocation by category (%):
Total plan asset allocation by category	10.00%	10.00%	12.00%
United Kingdom [Member]
Plan net pension (credit)/charge:
Interest cost on PBO	$ 11.2	$ 15.2	$ 15.0
Expected return on plan assets	(17.8)	(22.0)	(22.2)
Amortization of prior service credit	(0.5)	(0.9)	(1.1)
Amortization of actuarial net losses	0.9	(0.0)	2.0
Plan net pension (credit)/charge	$ (6.2)	$ (7.7)	$ (6.3)

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