Derivative Financial Instruments - Fair Value of Derivative Instruments, Designated and Qualifying As Cash Flow Hedges (Detail) (Interest rate contracts [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Other assets [Member]
Derivatives, Fair Value [Line Items]
Derivative Assets	$ 45	$ 29
Interest taxes and other liabilities [Member]
Derivatives, Fair Value [Line Items]
Derivative Liabilities	$ 274	$ 248