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Long-term Incentive Plan - Summary of Long-term Incentive Plan (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Disclosure of long-term incentive plan [abstract]      
Opening balance $ 2.1 $ 18.1  
Charge to income statement 9.1 1.1 [1] $ 5.0 [1]
Payments 0.0 (17.8)  
Translation adjustment 0.3 0.7  
Balance at end of the year $ 11.5 $ 2.1 $ 18.1
[1] Refer note 42.