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Supplemental Cash Flow Information - Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures (Detail) - USD ($)
$ in Millions
9 Months Ended
Sep. 30, 2015
Sep. 30, 2014
Supplemental Cash Flow Elements [Abstract]    
Additions to property, plant and equipment $ 121.1 $ 47.1
Plus: Increase in capital accruals 17.5 5.9
Asset retirement expenditures 0.7 1.0
Total capital expenditures $ 139.3 $ 54.0