Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Taxes [Line Items]
Income tax expense	$ 99.7	$ 95.0	$ 276.6	$ 268.2
Effective tax rate	32.80%	31.50%	32.80%	32.30%