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Environmental Trust Funds - Schedule of Environmental Trust Funds (Detail) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Environmental Trust Funds [abstract]      
Balance at beginning of the year $ 60.8 [1] $ 55.5  
Contributions from continuing operations 7.1 7.7  
Interest earned 0.7 0.6 [1] $ 0.5 [1]
Translation adjustment 0.9 (3.0)  
Balance at end of the year $ 69.5 $ 60.8 [1] $ 55.5
[1] Refer note 42.