Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		54 Months Ended			9 Months Ended	1 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Dec. 31, 2008	Nov. 30, 2006	Sep. 30, 2012 Scenario, Forecast [Member]	Nov. 30, 2006 Sold Warrants
Sold warrants to acquire shares of our common stock									215
Sold warrants to acquire shares of our common stock, exercise price per share							19.55
Common stock excluded from calculation of diluted earnings per share	5.2	17.6	4.3	15.4
Repurchases of Common Stock, shares authorized to repurchase						250.0
Total Repurchases of Common Stock, shares			15.3		211.2
Total Repurchases of Common Stock			$ 410.0		$ 4,100.0
Shares authorized for future repurchases	38.8		38.8		38.8
Plan to spend for the year on common stock repurchases								$ 700.0