Stockholders' Equity (Narrative) (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012
Stockholders Equity [Line Items]
Repurchased warrants for the purchase of the Company's common stock	$ 28	$ 13
Proceeds from sale of convertible note hedge	37	19
Net unrealized gains (losses) on cash flow hedges	0		0
Company's Vehicle-Backed Debt And Floating Rate Debt [Member]
Stockholders Equity [Line Items]
Net unrealized gain (losses) on cash flow hedges, before tax		12
Net unrealized gains (losses) on cash flow hedges		7
Floating rate vehicle-backed and corporate debt [Member]
Stockholders Equity [Line Items]
Net unrealized gain (losses) on cash flow hedges, before tax		11
Net unrealized gains (losses) on cash flow hedges		7
3 1/2% Convertible Notes [Member]
Stockholders Equity [Line Items]
Senior notes interest percentage	3.50%	3.50%
Repurchased warrants for the purchase of the Company's common stock	28
Proceeds from sale of convertible note hedge	$ 37
Change in net purchase and issuance of shares	3
Convertible Notes [Member] | 3 1/2% Convertible Notes [Member]
Stockholders Equity [Line Items]
Senior notes interest percentage	3.50%