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Provisions - Summary of Silicosis Settlement Costs (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Provisions [abstract]    
Balance at beginning of the year $ 31.9 $ 0.0
Changes in estimates (4.5) 30.2
Unwinding of provision recognised as finance expense 2.0 0.9
Translation (4.3) 0.8
Balance at end of the year $ 25.1 $ 31.9