Treasury Stock (Detail) - Schedule of Authorizations made by Board of Directors to repurchase Common Stock (USD $) In Millions, unless otherwise specified	1 Months Ended							51 Months Ended
	Sep. 30, 2010		Dec. 31, 2009	Feb. 28, 2009	Nov. 30, 2008	May 31, 2008	Dec. 31, 2007	Feb. 29, 2012
Authorization amount			$ 20.0	$ 5.0	$ 10.0	$ 20.0	$ 20.0	$ 119.0
Less repurchases made from December 2007 through February 2012								(80.1)
Remaining Board authorization at February 29, 2012								38.9
September 2010	$ 44.0	[1]

[1] Represents the remainder of $200.0 authorization after giving effect to the purchase of 5,199,699 shares at $30.00 per share pursuant to a modified Dutch auction tender offer that was completed by the Company on November 3, 2010, for a total cost of $156.0, excluding related fees and expenses. The Common shares purchased pursuant to the tender offer represented approximately 15.1% of the Common shares outstanding as of October 27, 2010. Fees for the modified Dutch auction tender offer were $1.2.