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Change in Working Capital - Summary of Change in Working Capital (Detail) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Disclosure Change In Working Capital [abstract]      
Inventories $ 0.8 $ (55.1) $ (39.2)
Trade and other receivables 15.0 (2.2) 2.8
Trade and other payables (32.1) (12.1) 34.1
Total change in working capital $ (16.3) $ (69.4) $ (2.3)