Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Taxes [Line Items]
Income tax expense	$ 94.7	$ 86.6	$ 173.2	$ 162.2
Effective tax rate	33.10%	32.50%	32.80%	32.30%