Summary of Significant Policies - Additional Information (Detail)

v2.4.0.8

Summary of Significant Policies - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Schedule Of Significant Accounting Policies [Line Items]
Amounts of tax included on a gross basis	$ 44.4	$ 37.4	$ 111.9	$ 104.0