Stockholders Equity - Additional Information (Detail) (USD $) In Millions, except Per Share data, unless otherwise specified	1 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended	3 Months Ended	9 Months Ended	1 Months Ended
	Sep. 30, 2012	Mar. 31, 2012	Sep. 30, 2012	Sep. 30, 2012 Common Stock	Mar. 31, 2012 Common Stock	Sep. 30, 2012 Common Stock	Sep. 30, 2012 Senior Subordinated Convertible Notes	Sep. 30, 2012 Maximum	Jan. 31, 2012 Maximum
Stockholders' Equity [Line Items]
Repurchase of common stock, authorized value								$ 250	$ 500
Repurchase of common stock, shares					12.1
Total purchase price of common stock		435
Shares repurchased under stock repurchase program, average price per share	$ 52.87	$ 36.00	$ 38.43
Net proceeds from senior subordinated convertible notes used for repurchase of common stock							$ 100
Repurchase of common stock, shares				1.9		14.0