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	Mar. 31, 2013		Dec. 31, 2012
Other assets
Derivatives, Fair Value [Line Items]
Fair value hedge assets	$ 42	[1]	$ 10	[1]
Interest taxes and other liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair value hedge liabilities	$ 668	[1]	$ 875	[1]

[1] The derivative asset and derivative liabilities presented above may be eligible for netting and consequently may be shown net against a different line item on the consolidated balance sheet. Balance sheet categories in the above table represent the location of the assets and liabilities absent the netting of the balances.