Supplemental Cash Flow Information (Summary of Reconciliation of Additions to Property, Plant and Equipment to Total Capital Expenditures) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Supplemental Cash Flow Information [Line Items]
Additions to property, plant and equipment	$ 78.6	$ 106.5
Plus: Increase (decrease) in capital accruals	12.9	(5.3)
Asset retirement expenditures	1.6	8.3
Total capital expenditures	93.1	109.5
Predecessor and Successor [Member]
Supplemental Cash Flow Information [Line Items]
Additions to property, plant and equipment			135.6
Plus: Increase (decrease) in capital accruals			3.2
Asset retirement expenditures			9.2
Total capital expenditures			$ 148.0