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Revenue - Schedule of Revenue (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Disclosure Of Revenues [Abstract]      
Revenue from mining operations $ 2,761.8 $ 2,666.4 [1] $ 2,454.1 [1]
[1] As Restated - Refer note 40 for further details.