Income Taxes - Roll-Forward of Unrecognized Tax Benefits and Associated Accrued Interest and Penalties (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Income Tax Contingency [Line Items]
Opening balance at January 1, 2013	$ 12.8
Additions for tax positions of prior periods	0.3
Reductions due to lapsed statutes of limitations	(0.6)
Closing balance at September 30, 2013	12.5
Current	(5.4)	(3.0)
Non-current	7.1	9.8
Interest and Penalties [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1, 2013	0.6
Additions for tax positions of prior periods	0.2
Reductions due to lapsed statutes of limitations	(0.1)
Closing balance at September 30, 2013	0.7
Current	(0.4)
Non-current	0.3
Unrecognized Tax Benefits [Member]
Income Tax Contingency [Line Items]
Opening balance at January 1, 2013	12.2
Additions for tax positions of prior periods	0.1
Reductions due to lapsed statutes of limitations	(0.5)
Closing balance at September 30, 2013	11.8
Current	(5.0)
Non-current	$ 6.8