Stockholders Equity and Share-Based Awards - Additional Information (Detail) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended		3 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended	1 Months Ended	12 Months Ended			1 Months Ended	12 Months Ended							3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	1 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Feb. 28, 2013 Accelerated Share Repurchase Program	Dec. 31, 2013 Accelerated Share Repurchase Program	Sep. 30, 2012 1 7/8% Senior Subordinated Convertible Notes due 2018	Dec. 31, 2013 Restricted Stock	Dec. 31, 2012 Restricted Stock	Dec. 31, 2011 Restricted Stock	Jan. 31, 2013 Restricted Stock Executive Officer Annual Grant	Dec. 31, 2013 Restricted Stock Executive Officer One Time Grant	Dec. 31, 2013 Stock Options	Dec. 31, 2012 Stock Options	Dec. 31, 2011 Stock Options	Dec. 31, 2013 Restricted Stock With Common Stock Price Thresholds	Dec. 31, 2012 Restricted Stock With Common Stock Price Thresholds	Dec. 31, 2011 Restricted Stock With Common Stock Price Thresholds	Dec. 31, 2012 Performance Based Restricted Share Awards 2010 Grant Executive Officer	Dec. 31, 2013 Performance Based Restricted Share Awards 2010 Grant Executive Officer	Mar. 31, 2012 Common Stock	Dec. 31, 2013 Common Stock	Feb. 28, 2013 Maximum	Jan. 31, 2012 Maximum	Dec. 31, 2013 Maximum Restricted Stock Y	Dec. 31, 2013 Maximum Stock Options Y	Dec. 31, 2013 Minimum Stock Options
Stockholders' Equity [Line Items]
Share-based awards collectively available for grant				6,300,000
Share-based awards explicit service period																												4 years	3 years
Share-based awards contractual term																											7	7
Total intrinsic value of options exercised															$ 6.8	$ 16.5	$ 18.4
Number of share options granted															0	0	0
Weighted average grant date fair values of awards										$ 55.38	$ 32.61	$ 19.03						$ 33.80	$ 18.98	$ 19.67
Restricted share awards granted				1,687,100									800,000	700,000								200,000
Aggregate grant date fair value of share-based awards													28.9	38.7								7.4
Common stock transfer restriction period														3 years
Unrecognized compensation cost related to non-vested share-based awards				24.1
Weighted average period to recognize compensation costs				10 months
Stock Based Compensation Recognition Of Cumulative Expense Not Previously Recognized																					33.6
Shares issued in equity offering	16,500,000																							16,500,000
Price per share received in equity offering	$ 47.00
Proceeds from issuance of common stock, net	745
Repurchase of common stock, authorized value																									500	500
Stock repurchase, amount paid			435				250
Repurchase of common stock, shares		2,800,000						5,600,000															18,100,000
Net proceeds from senior subordinated convertible notes used for repurchase of common stock									100
Per share average price of shares repurchased		$ 35.25	$ 24.00
Cash dividends paid to stockholders					$ 7.5	$ 30.1