Stockholders' Equity (Narrative) (Detail) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	9 Months Ended
	Aug. 06, 2013	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Stockholders Equity [Line Items]
Repayments of Convertible Debt		$ 53
Repurchased warrants for the purchase of the Company's common stock		30	26
Proceeds from sale of convertible note hedge		41	38
Net unrealized gains (losses) on cash flow hedges		1		0
Stock Repurchase Program, Authorized Amount	200
Stock Repurchased During Period, Shares		860,000
Stock Repurchased During Period, Value		25
Company's Vehicle-Backed Debt And Floating Rate Debt [Member]
Stockholders Equity [Line Items]
Net unrealized gain (losses) on cash flow hedges, before tax		1	11
Floating Rate Vehicle Backed And Corporate Debt [Member]
Stockholders Equity [Line Items]
Net unrealized gain (losses) on cash flow hedges, before tax		$ 1	$ 20
3 1/2% Convertible Notes [Member]
Stockholders Equity [Line Items]
Senior notes interest percentage		3.50%	3.50%
Change in net purchase and issuance of shares		3,000,000
Convertible Notes [Member] | 3 1/2% Convertible Notes [Member]
Stockholders Equity [Line Items]
Senior notes interest percentage		3.50%