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Environmental Trust Funds (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2021
Dec. 31, 2020
Dec. 31, 2019
Environmental Trust Funds [abstract]      
Balance at beginning of the year $ 79.3 $ 69.5  
Contributions 10.1 8.7  
Interest earned 0.8 0.7 $ 0.7
Translation adjustment (2.1) 0.4  
Balance at end of the year 88.1 79.3 $ 69.5
Term deposit 17.5 17.6  
Cash deposit $ 70.6 $ 61.7