Derivative Financial Instruments - Fair Value of Derivative Instruments that are Designated and their Location on Balance Sheet (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]
Fair value hedge assets	$ 9	$ 4
Interest taxes and other liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value hedge liabilities	$ 933	$ 1,134