Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended		24 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Jul. 31, 2014	Oct. 31, 2012
Stockholders Equity Note [Line Items]
Aggregate amount of common stock authorized for repurchase						$ 350.0	$ 300.0
Treasury stock acquired	$ 62.5		$ 222.4	$ 40.4	$ 280.6
Treasury stock, shares, acquired	148,231	0	549,853	113,160
Treasury stock acquired, average cost per share	$ 421.89		$ 404.55	$ 356.92