Schedule Of Effect Of Derivatives Recognized (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Schedule of Cost-method Investments [Line Items]
Derivative contracts	$ (30)	$ 11	$ 45
Interest Expense
Schedule of Cost-method Investments [Line Items]
Derivative instruments, gain (loss) recognized in operations	(32)
Derivative contracts		1
Transaction Related Cost
Schedule of Cost-method Investments [Line Items]
Derivative instruments, gain (loss) recognized in operations		(46)
Operating Expense
Schedule of Cost-method Investments [Line Items]
Derivative instruments, gain (loss) recognized in operations	1	27
Vehicle Interest
Schedule of Cost-method Investments [Line Items]
Derivative contracts		$ 2