Related Party Transactions - Schedule of Amounts Included in Financial Statements Arising From Transactions with GST (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Due from GST	$ 0.0		$ 0.0		$ 0.0
Accrued interest to GST	21.7		21.7		36.7
Accounts Receivable [Member]
Related Party Transaction [Line Items]
Due from GST	12.5		12.5		16.5
Deferred Income Taxes [Member]
Related Party Transaction [Line Items]
Income tax receivable from GST	111.7		111.7		100.6
Other Assets [Member]
Related Party Transaction [Line Items]
Due from GST	1.4		1.4		1.3
Accounts Payable [Member]
Related Party Transaction [Line Items]
Due to GST	7.8		7.8		8.0
Accrued Expenses [Member]
Related Party Transaction [Line Items]
Accrued interest to GST	16.2		16.2		$ 31.2
Net Sales [Member]
Related Party Transaction [Line Items]
Sales to GST	6.9	$ 7.3	13.6	$ 13.4
Cost of Sales [Member]
Related Party Transaction [Line Items]
Purchases from GST	4.6	5.4	9.2	10.7
Interest Expense [Member]
Related Party Transaction [Line Items]
Interest expense to GST	$ 8.3	$ 7.9	$ 16.6	$ 15.7