Stockholders' Equity - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2009	Dec. 31, 2011	Dec. 31, 2010
Stockholders Equity [Line Items]
Convertible note hedge purchased, gross		$ 95
Proceeds from issuance of warrants		62
Common stock subject to anti-dilution provisions		21.2
Convertible note hedge strike price		16.25
Warrant exercise price		22.50
Warrant expiration period (in days)	80 days
Repurchased warrants for the purchase of the Company's common stock	29
Proceeds from sale of convertible note hedge	43
Net unrealized gains (losses) on cash flow hedges		(106)	(13)	(46)
Companys Vehicle Backed Debt And Floating Rate Debt
Stockholders Equity [Line Items]
Net unrealized gains (losses) on cash flow hedges, before tax	21
Net unrealized gains (losses) on cash flow hedges	13
Floating rate vehicle-backed and corporate debt
Stockholders Equity [Line Items]
Net unrealized gains (losses) on cash flow hedges, before tax	19
Net unrealized gains (losses) on cash flow hedges	12
3 1/2% Convertible Senior Notes
Stockholders Equity [Line Items]
Senior notes interest percentage	3.50%
Repurchased warrants for the purchase of the Company's common stock	29
Proceeds from sale of convertible note hedge	$ 43
Change in net purchase and issuance of shares	13