Shareholders' Equity - Additional Information (Detail) (USD $)	12 Months Ended			127 Months Ended	12 Months Ended				12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2012	Dec. 31, 2012 Stock Options	Dec. 31, 2012 Stock Options Upper end	Dec. 31, 2012 Stock Option Plan 2012	May 02, 2012 Stock Option Plan 2012	Dec. 31, 2012 Employee Stock Purchase Plan	Dec. 31, 2011 Employee Stock Purchase Plan	Dec. 31, 2010 Employee Stock Purchase Plan	Dec. 31, 2012 Directors' Restricted Stock Plan 2008	May 31, 2008 Directors' Restricted Stock Plan 2008	Nov. 30, 1993 Non-Discretionary Plan	Nov. 30, 2001 Discretionary Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized for repurchase														40,000,000
Expected common stock shares issued and outstanding															200,000,000
Shares authorized for grant								3,000,000	9,305,452				200,000
Grants, maximum number of shares per person							100,000
Shares available for granting of awards							220,210					72,702
Award vesting period						5 years						1 year
Maximum contractual term					10 years
Purchase price percentage of fair market value									85.00%
Issuance of shares under stock purchase plan				7,339,020
Amount withheld employee stock purchase plan									$ 12,192,000
Fair value of annual grant per participant of restricted stock awards												200,000
Restricted shares granted												26,700
Weighted average fair value of award granted during the period									$ 9.70	$ 11.70	$ 11.16	$ 37.45
Total intrinsic value of options exercised	39,000,000	47,000,000	135,000,000
Total unrecognized share-based compensation cost	$ 91,000,000			$ 91,000,000
Unrecognized share-based compensation cost, weighted average period	3 years 1 month 8 days